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Topic: Detailed information about SPDIF (Read 7868 times) previous topic - next topic
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Detailed information about SPDIF

Hi everybody. I am so glad to join such a thriving and knowledgeable community.

I am a newbie who is planning on using his motherboard's SPDIF output and turn his PC into a Home Cinema, and I need some information about SPDIF, which I couldn't find in the motherboard manual, nor in the Internet, nor in these forums.

My motherboard is an Intel D865PERL with a AC'97 codec by Analog Devices. The driver is called SoundMAX 4 XL. Though I contacted SoundMAX for information on this matter, I haven't got any feedback yet. Business as usual.

What sample rates/bitrates/number of channels/audio formats does a conventional, motherboard-down spdif output support? I mean, is it possible to transmit 96KHz/24bits 7.1 uncompressed audio down the coaxial cable up to a audio receiver? Is there enough bandwidth to that? Or is it only possible to transmit uncompressed 5.1 audio at 48KHz/16bits? Or is it only possible to transmit compressed AC3 streams? Or DTS? Does it entirely depend on the attached audio receiver? I will appreciate any link to any comprehensive, though easy-to-read, SPDIF standard document.

Do I need any special software (Directshow filter or similar) to enable my video player to use the spdif output? In the mixer program bundled with the

Thank you!

EDIT: DigitalMan, what is IIRC?

Detailed information about SPDIF

Reply #1 –
AFAIK, most AC97-compliant motherboard sound controllers allow 48/16 linear pcm output and unprocessed AC3/DTS output (should be switchable through sound control panel) ... AFAIK, it depends on the dvd player software you use whether you are able to play back DVD's multichannel audio via SPDIF or not.

BTW: You will need an external AC3/DTS decoder for that ... like the ones built into home theatre receivers or even sourround active speaker sets ...
The name was Plex The Ripper, not Jack The Ripper

Detailed information about SPDIF

Reply #2 –
DTS mens also compressed/uncompressed 7.1 audio. Can a SPDIF output and the AC97 codec support 7.1 audio?

Must I accept, that 96/24 audio cannot be transmitted through SPDIF?

Detailed information about SPDIF

Reply #3 –
IIRC, SPDIF supports 2 channels up to 24 bits/96kHz, but no more channels, bit depth or sampling rate.  DTS and AC3 can also be passed up to 7.1 channels, but these are of course compressed.

AFAIK there is no common industry standard digital interface for connecting uncompressed digital audio > SPDIF channles or resolution.  There are some Firewire/5C solutions and some other proprietary ones in the pro and high-end gear, but they are not standardized very well.

The best hope is if the upcoming HDMI (High Definition Multimedia Interface) standard becomes accepted and implemented.  HDMI is for both digital audio and video integrated into one interface, so may not be exactly what you are looking for.

AC97 has 16 bit / 48kHz as the minimum implementation for SPDIF, so many low cost on-board implementations resample everything to 16/48.  AC97 does allow for bit exact SPDIF output as an option, but not all devices use it, and there may be some poor implementations of resampling to 16/48.  FYI, AC97 will be replaced later this year by Intel High Definition Audio, of which I don't know too much other than it is supposed to support up to 32bit/192kHz and at least 5.1 channels (I think; could be wrong).  I have no idea what physical layer Intel High Definition Audio can/is supposed to use, so stay tuned for the Intel chipset release.  The problem there is finding another device to receive the output of 32/192/7.1, etc.

I am not the definitive expert on this, just a spectator contributing my two Yen.
Was that a 1 or a 0?

Detailed information about SPDIF

Reply #4 –
Thanks DigitalMan. Your comments have raised some questions in my mind:

1-So, can you confirm that compressed, 7.1ch, 96/24 DTS audio can be conveyed to an extern receiver/decoder via S/PDIF? (It is not completely clear to me, and I need that exact wording to be sure) Besides, I derive from your answer that AC3 cannot be transferred in uncompressed format, but only compressed. Is that correct?

Transferring compressed data means that you have to buy a multichannel amplifier that includes a AC3/DTS decoder. That poses at least 2 problems: a) more features=>the amplifier is more expensive,  and b) there has to be more digital circuitry than actually necessary in the amplifier=>digital circuitry reduces SN ratio at the analog output=>More efforts have to be put on circuit layout design to increase SN=>the amp is more expensive. That, or the SN ratio is let be lower.

I haven't looked into high-end multichannel hi-fi amps myself, I guess I really have to ask:

2-does it much of a difference, as fas as price is concerned, buying a decoderless hi-fi amp or buying a hi-fi amp equiped with a decoder?

3-can you point out any of these propietary solutions running on Firewire? I guess those solutions will include a Directshow filter for channeling uncompressed audio to the Firewire port. Is that right? Anyway, I find that using Firewire is pretty "standardized", isn't it? Every PC has it, and it is a smart way to use existing infrastucture (i.e. not buying into HDMI when you have fine things already).

4-Do you know of any webpage where the S/PDIF standard can be downloaded, or can you provide me with the standard in an electronic format (pdf and the like)?


Thanks

Detailed information about SPDIF

Reply #5 –
there are short specs/history:
http://www.epanorama.net/documents/audio/spdif.html
PANIC: CPU 1: Cache Error (unrecoverable - dcache data) Eframe = 0x90000000208cf3b8
NOTICE - cpu 0 didn't dump TLB, may be hung

Detailed information about SPDIF

Reply #6 –
Quote
EDIT: DigitalMan, what is IIRC?

1. IIRC = if I recall correctly
Nothing but a Heartache - Since I found my Baby ;)

Detailed information about SPDIF

Reply #7 –
Whew, quite a lot of questions there pirata, I'll do my best with what I know:

1) Absolutely 7.1 DTS and AC3 can be transmitted via SPDIF.  That is how these signals get from DVD players and DTV receivers and computers to surround sound decoders.  AC3 is only transmitted in compressed format over SPDIF.

You do need a receiver or preamp with a decoder in it to listen to the DTS or AC3 signal.  To address your points:
a) More features does = more expensive.  How big a problem that is depends on your personal budget.  To a billionaire this is a non-issue, to a college student it may be.  You can get a DTS/AC3 surround sound receiver for about $150, so this isn't a huge expense.
b) More digital circuitry - yes, certainly.  Unnecessary circuitry - well, if you want to listen to DTS or AC3 then these are necessary circuits.  Digital circuitry reducing S/N at the analog output - I don't necessarily agree.  Competent circuit design with good trace routing and power supply regulation should keep this from being an issue - certainly not one that you can hear and shouldn't add tremendously to the cost.  If there are computer sound cards with S/N ratios over 100dB I would worry more about the design implementation and drivers than where the decoder resides.

2) Difference in price with / without a decoder?  Well yes, one with a decoder is going to be more expensive.  You have to decode somewhere, so the decoder is either in the sound card, the DVD player or the amp/receiver.  You may get a cheaper amplifier with only analog inputs, but if you are looking for a multichannel amplifier you may or may not save money - analog input multichannel amplifiers tend to be higher end beasts which will be considerable more expensive than a mass market receiver with multichannel capability.  But you may be able to find multichannel analog low-end receivers - I haven't looked.

3) Proprietary Firewire I remember are from Pioneer and Denon, possibly others and each is only meant to connect to receivers from that same manufacturer.  The pysical layer is Firewire, but it is audio data encrypted with 5C and I don't think you can record it with a PC unless you break the encryption.  I know that Meridian has a proprietary link, and I think there are some others.  I have tried to tune this mess out until a standard emerges, so I may be off on the details.  The fact that they all have different names is the first red flag of incompatability.

SPDIF specification?  I think it is technically referred to as IEC-958, so you should be able to find it via Google.  [Edit: smok3 beat me to it, thx]

When thinking about where to decode the surround stream, remember that the ability to adjust crossovers, levels, delays , and any filtering (EQ, THX processing, etc.) vary widely in how they are implemented in different decoders.  You may want to put more value in the flexibility of channel management than in where the decoder chip resides.

Note:  IIRC = If I Remember Correctly [Edit: Digga beat me to this one, thx]

Edits: noted redundant resopnse
Was that a 1 or a 0?

Detailed information about SPDIF

Reply #8 –
Several things:

I am extremely doubtful that ADI SoundMAX even supports 24 bit pass-through regardless of the fact that the interconnect can physically handle it.
You will almost certainly be getting 16/44.1 and 16/48 (or less) only out of the digital output.

Amplifiers with integral decoders are not particularly more expensive these days than models without because decoders are cheap, and in fact multichannel amplifiers without decoders tend to be the more esoteric high end models.

You could of course buy an analog input only multichannel amp, but you would quite likely have to spend more than one with a decoder, and then would require DVD software that supported dts and DD (often you have to pay more for dts support than just DD) decoding. Most all DVD software players I've used support digital pass-through without additional fees for decoding functionality.

Whether the CPU algorithm is superior at decoding the signal properly than a particular hardware decoder probably depends on the algorithm and  the hardware decoder, but they should be ideally doing exactly the same thing.

In addition, with analog output you would be relying on the ADI SoundMAX CODEC to act as a DAC, when in all likelyhood a decent decoder-equipped reciever would have higher quality internal conversion. By using the digital output you bypass the DAC function of the CODEC and opt to use the one in the reciever, which does not inevitably result in more circuitry (-1, +1).

Regardless, since you will require a separate reciever and will almost be forced into buying a model which features internal hardware DD/dts (more for NEO:6, DD EX, dts ES, etc.), you can experiment to find which way you prefer.

It's possible you could find an older reciever that does Pro Logic decoding and features six-channel analog input, but it will almost assuredly be used.

Detailed information about SPDIF

Reply #9 –
Nice answers. Let's see:

0-When you say 7.1 DTS is allowed through spdif, you also mean 96/24?
I've had a look at the standard. It says 48/24 is allowed uncompressed, but the number of channels is not specified for uncompressed. They could be more than stereo! How many channels can be supported? Only 2 for sure?

1-I think it is far better decoding in the PC CPU and sending uncompressed to the receptor: if one day a new compression standard for audio is introduced, you cannot decode it in the receptor (it is hardware! Can't change it!), but you do can in the PC. The problem is "sending uncompressed".

2-I thought Firewire would be a clever solution: everybody has it. You plug the amp in and done: uncompressed digital audio all the way down to the DAC. Are you sure you just cannot plug a PC through firewire in such receivers?? Using some propietary software from Denon/Pioneer??

3-decoding algorithm: as far as I know, thinking whether a software algorithm is better at decoding than a receiver is a waste of time. They do the same steps. They produce the same samples. The real important decissions are done at encoding, any you can't intervene in that.

4-One technical question: a multichannel amp is 3 to 4 times a stereo amp in terms of circuitry. That means either they cost a lot (haven't look into them a lot, actually), or they are... a little crappy, to keep the price affordable. I mean, as far as audio quality is concerned, a 450$ stereo amp must be faaaar superior than a 450$ 7.1 amp. What's your point on this, gents?

5-@audible!:  about the SoundMAX, when you say 16/44.1 and 16/48, you mean STEREO, don't you? No 5.1, no quadraphonic, nothing but stereo, right? SoundMAX suport makes me sick. The help files to the driver interface is simple bullshit. The web support is rough... I just don't know what does the SPDIF output support and what not!! I  have just 2 check boxes "AC3 OUTPUT" and "PCM OUTPUT". What do you think that is?

Detailed information about SPDIF

Reply #10 –
pirata, I'll try to answer these:

0)  0?  Wouldn't happen to be an engineer?  Anyway, compressed can not be specified in the SPDIF document because the data encoding is proprietary for AC3 and DTS.  So, for linear PCM (L-PCM) SPDIF can carry up to 96/24 for 2 channels only. 

Compressed (DTS/AC3) it will depend on the data rate, sampling rate, compression rate, etc. during mastering - they are just transmitted using SPDIF as a transport.  In fact, early decoders which didn't recognize the DTS/AC3 flags would try to decode the compressed datastream as L-PCM resulting in pure noise.  IIRC, I think most DVD multichannel soundtracks run between 320 and 480kb/s, so bandwidth is not an issue for the SPDIF link.  Multichannel L-PCM would definitely be a bandwidth issue if SPDIF even supported it (which I don't think it does).  Remember that 7.1 DTS/AC3 is just 5.1 with two channels matrixed in the 5.1 - kind of like Dolby Pro Logic in the analog domain; they are not discrete channels in the recording.

1) Decoding in the PC - well yes, you do gain the flexibility of software updates, but transmitting it is definitely an issue.  Plus, why use CPU cycles for DTS/AC3 when there is a dedicated hardware processor in the amplifier available?  I don't see new multichannel formats coming any time soon, so the flexibility question doesn't concern me too much.  Maybe HDMI, but that is a ways away still and for DVD movies and DTV the SPDIF link is all you need.

2) Firewire - in theory it is a very clever solution.  I have not seen any consumer PC software that creates 5C encrypted multichannel audio streams, certainly not from Denon/Pioneer.  I have never heard of anyone doing this.  The Audigy2 is the only sound card I know that can decode DVD-Audio for example, and it also has a Firewire port on it, so you may want to check out whether it could connect digitally to a receiver.  I am almost 100% sure you can't get it to work, but I could be wrong.  Anyone else know?

3) Decoding - I agree that sample for sample the audio stream should be identical whether it is decoded in hardware or software.  My point is that the configuration flexibility may not be equal - how flexible are the bass management settings, etc.?  In my limited experience the higher end receivers / preamps are much more flexible in configuring the final output to the speakers than the software decoders I have seen.  If you are picky about your sound, then getting the crossover slopes, frequencies, phasing, delays, etc. correct can have a significant audible difference.  I am not that familiar with the flexibility of the software decoders, so there may be some very good ones out there.  For example, my multichannel preamp allows me to set the crossover to be a "phase perfect" filter type with 24dB/octave slopes at 60Hz for the main speakers, 80Hz for the center and 50Hz for the surrounds.  I have measured the response in my room to know that this is the best measuring and sounding crossover as it results in the system response in the room.  If you need that level of flexibility, you need to check out the user interfaces of the hardware vs. software decoders.  If you don't care, then ignore this point.

4) Amplifier performance - This is a really complicated question, actually.  Because most people just buy multichannel receivers the volume is very high and they are not expensive to make.  Some high-end analog amplifiers are extremely low volume and therefore cost signficantly more to make than a multichannel receiver with 10x the circuitry.  The price on a decoder chip is much less when you buy 1 million of them than if you buy 1,000.  Then you need to factor in price premiums for brand name and this becomes pretty complex fast.  Just like in cars, if you want cheap you don't buy a Dodge Viper which may have less parts than a 4 door Honda Accord.  If you want cheap, buy the mass market product.  You may buy one of the higher end models to get more performance / features, but don't assume that price and cost and performance have anything to do with each other necessarily.  You can get a decent sounding 7.1 multichannel receiver for $400 and a decent 2 channel analog power amp for $1,500.  Is the 2 channel amp "better sounding?"  Maybe, but only you can decide how much the sound quality/brand image/flexibility is worth.  You could buy three $400 receivers and throw them out when technology changes for the price of the 2 channel amp.  I'm exaggerating to make the point - don't take the example literally.

5) Output - I would assume that "AC3 output" passes the undecoded AC3 stream on the SPDIF output to an external decoder while "PCM Output" decodes the AC3 stream and demuxes it into 2 channels, probably 48/16 L-PCM for stereo or Pro-Logic playback.
Was that a 1 or a 0?

Detailed information about SPDIF

Reply #11 –
Quote
about the SoundMAX, when you say 16/44.1 and 16/48, you mean STEREO, don't you? No 5.1, no quadraphonic, nothing but stereo, right? SoundMAX suport makes me sick.

I'm sure it'll do 5.1 passthrough no problem, provided it's not 24 bit passthrough, which I do not believe it in any way supports. Quadrophonic content will most likely not work unless it is preencoded DD/dts content (missing the center and LFE channels - which I've not seen).
Quote
One technical question: a multichannel amp is 3 to 4 times a stereo amp in terms of circuitry. That means either they cost a lot (haven't look into them a lot, actually), or they are... a little crappy, to keep the price affordable.


    Yes and no. Inexpensive multichannel surround amps commonly use shared power stages, but of course the amplification is separate.
    The question to ask is whether a stereo amp at the same price level as a multichannel amp has the same profit margin as the multichannel amp.
    These days the margin is quite likely higher on the stereo amp because of limited demand. Undoubtedly at the very low-end, multichannel amps are lower quality than stereo amps, but this does not appear to be necessarily true overall.
    I wouldn't spend $100 on a "5.1" amp (but you could probably get a stereo amp that has no noise issues new for that price), but you can get quite acceptable multichannel amps from Yamaha, Onkyo and h/k for two and three times that, especially on-line and even more so if you don't mind refurbs.

fixed tags

Detailed information about SPDIF

Reply #12 –
So, in summary (correct me if I am wrong): SPDIF can transmit both AC3 and DTS in compressed format. It can do it in 48/16 an 96/24, as long the stream is compressed and the bitrate is not too big (which always is the case). In uncompressed format, 16/44.1, 16/48 and 96/24 are allowed, but only for 2 channels, and they are not always implemented in motherboard-down audio solutions.

Right?

@DigitalMan: there othre formats, such as 5.1 vorbis, AAC (in 2 flavours), and MPEG4 (it's not AAC, is it?), and others to come. You could get material in those formats, and you couldn't listen to it in all its glory without CPU decoding.

What does "matrixed" exctly mean? How can 2 channels be recovered from one single channel without losses?

Quote
"why use CPU cycles for DTS/AC3 when there is a dedicated hardware processor in the amplifier available?"

Because I have zillions of CPU cycles to spare, and because I don't like to buy hardware. It gets old-fashioned with time.  ;-)

I'll have a look at Audigy2 and others, and I'll come back to you.

@Audible!: you mean 96/24 is not allowed in compressed format!?
How can a power stage be "shared"!?!?

I made the point about multich amps being crappy because we talk about LOTS of channels. It is necessary to keep price reasonable, so an unavoidable drop in quality HAS to happen. Reality is reality.

Detailed information about SPDIF

Reply #13 –
One question: spdif differentiates PCM streams from compressed streams with one flag bit. If that bit is 1 (I think), the receiver will know that the stream is compressed and it has to be decompressed before DAC. I don't know how a receiver can tell whether the incoming stream is AC3, DTS or MPEG. There are 2 possibilities:

1-there's a flag in the spdif stream that says whether it is ac3, dts or mpeg (I don't think this is true. I think ac3 was introduced many years after spdif was standardised. I could be wrong, though).

2-there's no "compressed stream type flag", and the receiver has to look at the data and decide what it is. If that's right, then things like 5.1 ogg, or 5.1 AAC, or 5.1 MPEG4 audio could be delivered via spdif, providing they were supported by the receiver. If this is right, spdif is susceptible to be useful in the future. It has enough bandwidth to transmit anything as long as it is compressed and under 1.4Mbps, and any compressed format can be sent via spdif as long as the receiver on the other side supports it.

I know this is only theoretical, because audio manufacturers are big grey elephants, unabe to move their asses to the pace of the geek community. That's why I love software.
Anyobody can say something about this? Is it 1 or 2?

----------

I have looked at Audigy and Co. and they actually work through USB. No spdif, no ieee, so there is enough bandwidth to send uncompressed multichannel digital audio directly to the card, letting decoding happen in the CPU. The problem is that I found no commentary on whether this is possible or not, and the card itself decodes DTS and AC3. I've tried to ask Creative, but the fine nice lads at Creative won't help anybody unless he has spent fat bucks in some of their products. This means, the e-mail support form needs a valid serial number of a Creative product. If you're no costumer, there's no help. Cool.

By the way, the audigy is only a sound card. You still need a power amplifier, and the audigy and similars have none, have they?

So, as said before in this thread, the only hope is HDMI. How far away is it yet? Are there products with it already? How is it applied in audio? Are there cables that somehow separate audio and video?

---------------

Also, I am thinking about all this multichannel stuff, and I've come to the conclusion that I don't really need to have lots of speakers arround in my living room. I'd rather use Dolby Virtual Surround to get surround feeling with just 2 (really good) speakers. The LFE channel would still need a subwoofer, so I'd had to have one. 3 speakers is fine with me. Is there any (good) receiver that features Dolby Virtual Surround, or is it a rare feature? Are those receivers prepared to drive only 2 speakers and a subwoofer, or is it bad for the amplifier?

I am looking into some brands (Harman-K, Denon, Marantz...), but I get easily lost. Too many features I can't understand. Do you know of any web page explaining all the tech lingo about hi-fi amps, in a human readable way?


----------------

One last thing: do you know brands of audio cards for professional music creation? I intend to buy one in the future, because I am myself sort of a musician. I am thinking right now a pro sound card could give a solution to this issue. I just need some brand names to look into.


Thanks

Detailed information about SPDIF

Reply #14 –
Hey boyz! Not willing to answer anymore?

EDIT: I've been checking out receivers by Denon, Harman/Kardon and Marantz, and they include inputs for VIDEO!!! What are they for? What can a power amp do with video signals??

Detailed information about SPDIF

Reply #15 –
Quote
Hey boyz! Not willing to answer anymore?

EDIT: I've been checking out receivers by Denon, Harman/Kardon and Marantz, and they include inputs for VIDEO!!! What are they for? What can a power amp do with video signals??

AFAIK they are there so that your amp will determine the video on your TV and thus you only have to change the source on the amp (eg. cable to DVD) instead of changing the audio source on the amp and then changing the video souce on the TV.  Personally I don't like this because the extra cords and connections *could* reduce picture clarity (and I don't want to bother buying the extra cable).  Does this make sense?
gentoo ~amd64 + layman | ncmpcpp/mpd | wavpack + vorbis + lame

Detailed information about SPDIF

Reply #16 –
pirata,
Some additional content for ya:

I understand that there is a flag that identifies compressed (non L-PCM) data.  Initially it was only used to identify AC3, but with DTS added it is up to the receiver to guess whether the data represents AC3 or DTS - or anything else you might send down the pipe.  The bandwidth is actually greater than 1.4Mbps, I think.  If  you take 96kHz x 24 bits x 2 channels you get  about 4.6Mbps + overhead.  So if you wanted to you could theoretically send AAC, OGG, MPC, etc. down SPDIF.  I don't know how to get the data in the output or how you would get it out at the other end, but in theory it would be possible.

OT: there may be multichannel formats for AAC, OGG, etc., but where would you get the content?  DVDs and HDTV use AC3 or DTS - I'm not sure you will ever have a significant commercial channel to get non AC3 or DTS content - maybe WMA with HD-DVD, but that is quite a ways away from commercial reality.  For multichannel you will have content available in AC3, DTS and the crippled DVD-audio and SACD discs for now and you can't access the last two datastreams easily, so I don't see much need to worry about other multichannels formats.  Just my $ 0.02.

There are a few products with HDMI that have been announced at the Consumer Electronics Show this year.  I think Panasonic showed a DVD player and companion receiver with HDMI.  You can Google for HDMI info - check out :
HDMI.org for example to get the full specification.  HDMI is like DVI plus encryped multichannel high resolution audio on one small connector.  It can support up to 192/24 for two channels and 96/24 for 8 channels.  HDMI may or may not be the "next big thing."  Many "advances" have been promised over the years, few make it to commercial success.  It may be a few years before the verdict is in on HDMI.

Earlier question re: lossless matrixing.  Matrixing is definitely not a lossless process - you don't get a perfect reconstruction when you matrix a channel between two channels and then decode it.  But, with some signal processing it can work well enough.  DTS/AC3 use matrixing to go beyond 5.1 (7.1, etc.).  The matrixed channels are in the side or center sourround channels, so they are not quite as critical as the front 3 and the matrixing losses are typically not a problem.

I don't understand why you ask about the ability to pass 96/24 multichannel data when you are willing to use a "virtual sourround channel."  This is kid of like acoustic matrixing.  It can work reasonably well, usually in one fixed listening position, but I would really recommend at least putting a 5.1 array for surround sound together.  You can probably pass on the 6.1/7.1 configurations, but the virtual surround is a pretty significant compromise in the context of high purity of signal transmission.  Have you heard it?

There are a few receivers out there that do Dolby virtual - they change so frequently I don't keep up on them.  I think there is software that would allow you to create the signal in the PC.  You may want to reconsider that center channel too at this point - it  is mainly for large screens (like movie theaters and large home theaters) where people will be sittting significantly off center from the screen.  The center channel helps anchor the sound to the picture.  If you don't have a large system you can do fine with two good front channles.

Feature overload is a problem in audio equipment.  Suggest you search this board and check out a site like Crutchfield, etc. to get some guidance.  Happy to help you on a PM basis if you would like.

Search Hydrogen audio for lots of discussions on sound cards.  There are many good ones available.  I've seen good product for professional use from E-Mu, Terratec, Digital Audio Labs, M-audio, etc.  None of these typically have power amplification in them - that is usually done in the speakers or with a separate power amp/receiver mostly because of power and space considerations in a PC card.

Not sure how we can help you - if you are willing to use virtual surround you should be fine with SPDIF, which is easy to implement with a large number of sound cards and inexpensive receivers or powered speaker systems.  Not sure why you would be interested in HDMI if you aren't looking to create a high performance multichannel speaker system.
Was that a 1 or a 0?

Detailed information about SPDIF

Reply #17 –
Quote
AFAIK they are there so that your amp will determine the video on your TV and thus you only have to change the source on the amp (eg. cable to DVD) instead of changing the audio source on the amp and then changing the video souce on the TV.  Personally I don't like this because the extra cords and connections *could* reduce picture clarity (and I don't want to bother buying the extra cable).  Does this make sense?

I don't use them for the same reason as you, but I wonder if the quality degradation is really that much?

It's a pain having so many inputs on the back of an a/v amp, especially when reaching round to plug something in. When I look at it, there's only 12 of those holes that I use 

Detailed information about SPDIF

Reply #18 –
Thanks for your help this far, DigitalMan.

Well, the answer is NO, I haven't tested thouroughly Virtual Surround. I just guessed it would create the feeling as well as a real system, because I have a little insight in what is done, and seems relatively simple. I need your expertise here: does Virtual Surround provide a good surround feeling, or does it not? If not, I'll go real, instead of virtual. No problem with that. I'm all for quality, really.

One question comes to mind now. When checking Marantz and co.'s websites, I found that those top-notch brands do use small speakers to deliver 5.1/7.1. I've always thought that those small devices just cannot produce good sound. I guess there is a lot of mythology about huge speakers. Is there any consensus on this? Are tiny satellites OK?

Also, the video connectors in the audio decoder still don't make sense for me. Source switching?? You mean all inputs are converted to a sole output format? What is it? Component, or DVI?

Well. After some checking in my AC97 codec specs, it seems that my spdif only supports 16/44.1 and 16/48. It is still enough bandwidth to do almost anything. The sad thing is that you cannot go software at decoding, but you have to go hardware, and buy an expensive power amp that, well... will cover almost everything (as long as digital (HD)TV stays AC3 and DTS). It's a pity that there is no brand that markets a updateable receiver, just like the DivX player.

Thank you for your PM offering.

Detailed information about SPDIF

Reply #19 –
I have heard Virtual Surround work okay - how effective it is is a subjective question.  I suppose only you can determine if it is acceptable.  I personally have discrete surround speakers because I wasn't satisfied with the Virtual performance - you may disagree.

Typically large speaker enclosures are required for efficient low frequency reproduction.  Small speakers can be very effective from the upper bass (>80Hz or so) through the treble, and even have advantages of having rigid enclosures, easy to place / mount in the room, small front baffle makes for effective high frequency dispertion, etc.  With decent subwoofers and crossovers a smaller satellite may even be preferrable.  You don't need a huge speaker to reach 80Hz, and if the lower frequencies can be handled by an efficient subwoofer then you can put a reasonably priced system together.  My only recommendation would be to try to match the model/manufacturer of the satellite speakers as much as you can, especially for the front 3 because it really makes the sound integrate better between channels.  And speaker models change frequently so if you don't buy them as a set you may not be able to add similar additional speakers later.

I think with the high volume of surround receivers you won't pay much price penalty at all for using a multichannel hardware decoder.

I do recall reading about some receivers that were software updateable - it was one of the mass market Japanese brands.  You'll have to do some research, Onkyo maybe?  Of course, there is the credibility issue of whether they will ever actually release a software update...There are some higher end preamplifier manufacturers that offer card-based, updateable surround processors.  They are more expensive than the non-updateable ones, so you'll have to do the tradeoff analysis.

Video connectors in the audio receiver is typically just source switching - actually pretty nice if you have the right connections.  Of course the format conversion discussion is tricky, so it often doesn't work out quite as nicely as it might.  There is that HDMI idea again 

Standards and technology have always been in flux, and the consumer electronics industry is not terribly good at standards in general (IR remotes, RCA jacks /speaker connectors, interoperability of control, etc.) so at some point you may be best served by just getting something that works well now and enjoying it until something significantly better is available later.
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Reply #20 –
I've been having a look at PRO-level sound cards by the likes of M-Audio, Terratec and company. They are all PCI, internal cards that carry out DA conversion inside the PC, what is not the most benign place to do it. The real problem is that I can't really tell if the noise and distortion figures are good or bad. What are normal values for SNR, THD, dynamic range, etc for Pro sound cards?


EDIT - I am looking at Onkyo now, and really have to ask: are 5.1/7.1 multichannel amps 3/4 times bulkier than stereo amps in terms of circuitry!?!? It is really a lot!

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Reply #21 –
Quote
They are all PCI, internal cards that carry out DA conversion inside the PC, what is not the most benign place to do it. The real problem is that I can't really tell if the noise and distortion figures are good or bad. What are normal values for SNR, THD, dynamic range, etc for Pro sound cards?

Not quite all of them. For example, Terratec's EWS88 carries an external DAC/ADC.

The insides of a computer is indeed electrically a pretty noisy place, but most high end soundcard manufacturers have managed to shield their cards well enough against the electrical storms occurring inside the computer case. Most of these internal 24/96 cards have better SNR and THD values than high end CD players. The SNR of these cards usually approaches 100 dB even for loopback recording, which is an exceedingly good value. Dynamic range is limited by the SNR. A good THD value is somewhat black magic; some high-THD amps sound a lot better than some low-THD amps. As long as it's smaller than a percent, it should be good

Search this board (and google) for Terratec and M-audio reviews, you'll find plenty of information.

Quote
I am looking at Onkyo now, and really have to ask: are 5.1/7.1 multichannel amps 3/4 times bulkier than stereo amps in terms of circuitry!?!? It is really a lot!


Well, it depends on the implementation, but basically yes. 7.1 channel amplifier manufacturers need to cram 4 times more op amps than in stereo amplifiers into the box. And furthermore all that needs to be of similar size and similar price with stereo amplifiers. There's bound to be some compromises.

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Reply #22 –
What's loopback recording?

Quote
" Most of these internal 24/96 cards have better SNR and THD values than high end CD players."


What do those measures refer to? The noise you get in an output when you play back a piece of music you recorded from some source before with the same soundcard? Or what?

How can a higher THD sound nicer?? That's good for guitar amps with valves, not for audio systems intended to reproduce a recorded sound with high fidelity.

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Reply #23 –
Quote
What's loopback recording?

Quote

" Most of these internal 24/96 cards have better SNR and THD values than high end CD players."


What do those measures refer to? The noise you get in an output when you play back a piece of music you recorded from some source before with the same soundcard? Or what?

How can a higher THD sound nicer?? That's good for guitar amps with valves, not for audio systems intended to reproduce a recorded sound with high fidelity.

Loopback recording is connecting the output to the input and recording the signal you are playing after going through a "loop" [loop of output back to input].  It tests the D/A conversion and A/D conversion together as a "loop."  Its a way of basically determining the overall quality of the output and recording capability of the card.

I think the quote actaully reads "better SNR and THD" not "higher" and yes, THD is better if it is lower, SNR better if higher.

SNR = signal to noise ratio, ratio of a pure tone to the background noise.  16 bit systems theoretically can obtain a SNR of 96dB, and many soundcards can exceed this figure.  24 bit is theoretically capable of 144dB, although I have never seen any real world electronics come close to it.

THD = total harmonic distortion; level of all non intended signal components in a signal as a % of the original intended signal.  Rule of thumb is anything < 1.0% is difficult to hear.
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Reply #24 –
Quote
What do those measures refer to? The noise you get in an output when you play back a piece of music you recorded from some source before with the same soundcard? Or what?

It should be the noise added to the output signal while playing a digital signal obtained from some different source than the sound card, such as by ripping the CD or transferring a signal from a CD player via SPDIF.

Usually hardware review sites quote the loopback recording SNR which is a lot lower than plain playback SNR because it adds noise both from playback and recording. But even the loopback SNR is often about 100 dB, whereas plain playback SNR can be somewhere between 110-120 dB. That is an excellent SNR value for any sound system in the planet.

Quote
How can a higher THD sound nicer?? That's good for guitar amps with valves, not for audio systems intended to reproduce a recorded sound with high fidelity.

Basically it's because a THD value doesn't tell you everything. Years ago, it turned out that some low-THD-amplifiers sounded worse than amps with a lot higher THD. This led to the discovery of intermodulation distortion (IMD) in amplifiers.

The human ear doesn't object much to harmonic distortion -- actually a number of people find a given piece of music more enjoyable to listen to when a small amount of harmonic distortion is applied to it. Electric guitar is an extreme example of this.

Some people still use high-THD valve amps and call that hifi, and I've seen quite a few audiophiles which swear that the invention of the transistor was a mistake