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1
AAC - General / Re: xHE-AAC. Is it ready yet? Any encoders out there?
Last post by polemon -
So I gave http://stream.radioh.no:443/ a try.

Listening / Getting the Streamdump
Thanks to mpv, youtube-dl, and ffmpeg, listening to the /rh.x16 stream is actually possible on Linux, and I'm pretty sure on Windows, too. However, it seems the toolchain is kinda struggling as it is.

Simply playing the stream directly with mpv, is quite low on errors:
Code: [Select]
$ mpv http://stream.radioh.no:443/rh.16
yields the following error right at the start:
Code: [Select]
[ffmpeg/audio] aac: channel element 2.15 is not allocated
Error decoding audio.
however right after that, the stream starts playing quite nicely.

Data Specifics
With the help of youtube-dl, I managed to download a sample length of the stream.
Inspecting it with ffmpeg yields this:
Code: [Select]
[aac @ 0x59159c0] Estimating duration from bitrate, this may be inaccurate
Input #0, aac, from 'rh-rh.16.part':
  Duration: 00:09:45.52, bitrate: 16 kb/s
    Stream #0:0: Audio: aac (HE-AACv2), 32000 Hz, stereo, fltp, 16 kb/s
Note the "16 kb/s". The Duration is out by around 20 seconds, in that ~10min sample. The file is 1189420 (1.2M) bytes in length, and is a pure AAC dump.

I can play the file back using mpv, but ffmpeg complains about "Reserved SBR extensions is not implemented", which seems to be kindof a minor thing (?), as the file plays alright.

When playing this file with "--msg-level=all=v", playing the stream directly with the switch using mpv, or inspecting the file with ffmpeg, it never mentions "xHE-AAC". Instead, the AAC stream is identified as HE-AACv2.

Tool Versions
My youtube-dl version is: "2018.01.21" (probably not the latest one).
I tried two versions of ffmpeg, "3.3.7" and "N-45774-g223f3dff8-static https://johnvansickle.com/ffmpeg/" compiled just a couple days ago.
mpv version is: "0.27.2".

I'm using Fedora 27.

Sound Quality
Since no log output of any of the tools I've used reports anything about "xHE-AAC" or "USAC", I'm not sure whether the USAC component is simply ignored. FFmpeg reports "HE-AACv2" with 16 kb/s, and that's pretty much it. Since all tools here use ffmpeg as back-end, I guess this isn't a surprise.

Having said that, the stream sounds "OK", given the low bitrate. However any sounds resembling noise, like someone making an 's', 'f', 'sh', or 'z' sound etc., sound all alike, and incredibly harsh. Similar to a cassette tape recorded with DC bias. Another analogy is perhaps very small speakers, like the ones you'd find on a cheap cellphone or an old 80's pocket radio. I imagine playing that stream through the speakers of a cellphone or cheap bluetooth speakers would be adequate; I wouldn't want to listen to it in my car, though. FM radio sounds much cleaner than this.

If anyone cares, I can upload a sample, together with one or two samples of one of their higher-quality streams for comparison.

Given that I don't know whether my tools are decoding the stream correctly, I'm unsure whether the (subjectively) bad sound quality is down to xHE-AAC simply being used with such a low bitrate, or if it's down to my tools not being able to decode the stream correctly.

Still haven't figured out a way, to create my own sample of xHE-AAC encoded audio. AFAIK, there are no encoders freely available, etc.
2
Audio Hardware / Re: Subwoofer advice needed
Last post by ajinfla -
Agreed, if more than one listening seat is involved.
It has nothing to do with seats and everything to do with mono (one sub) having zero chance of reproducing inter-aural spatial effects/lateralisation etc, as has been covered many times here, including many AES links by your truly. Einstein rules of insanity applies.

By what metric(s)?
All. Nearfield = zero modal problems at seat. Nothing to "correct" (and/or "incorrect" elsewhere).
Only issue might be phase due to propagation delay vs the mains, but the lower you cross, the less that matters as the low pass filter of the sub will automatically introduce a delay...and it will all appear in the frequency domain at given crossover, so easily measured (though not necessarily heard, depending on Q of any notch).

Please read, there are links to over 40 studies compiled https://secure.aes.org/forum/pubs/conferences/?elib=17270

4
Scientific Discussion / Re: Have a working 'expander' based on DolbyA (not same design) -- works well.
Last post by jsdyson -
Your terminology is slightly confusing.  It's not surprising for a studio tape since 1965 have been Dolby A encoded; it is surprising for it not to have been decoded for commercial release .  So your concern is really 'Dolby A encoded stuff released without decoding'.

AFAIK, Dolby A decoding was not available on any consumer playback gear (e.g reel to reel decks).  So no Dolby A 2TRK tapes would have been released commercially, unless it was by mistake.  Yet you say you have  "a 2TRK copy, unprocessed and is a DolbyA master of ABBA Gold and MORE ABBA Gold."    What gives you absolute certainty that these tapes are what you say? 

Given all the adjustments to EQ and dynamic range available to CD mastering engineers, I just don't see how you can be certain that commercial releases are suffering from Dolby A nondecoding, versus normal mastering choices.   Tipped up treble is hardly rare in CD masterings, and neither is compression, and both are easily achieved without Dolby NR playing a role.

Yet you go on to claim:
Quote
Believe it or not, often the better quality disks tend to leave the DolbyA undecoded -- it is the horridly misprocessed material that isn't usefully DolbyA encoded.

I don't see how you can *know* this.

However, you also say you have 'PROVABLY' Dolby A encoded material . If that is so, then you can do the comparison I mentioned previously  (decode with a Dolby A hardware decoder vs your software).

But there's also the whole issue of the Dolby calibration tone, which would only be printed to the master tapes;  without that, setting levels for decoded playback, is guesswork....





As I wrote above -- we have done careful comparisons between a real DolbyA unit (cat 22 based/360-361), and my decoder.  My decoder works generally better than the original DolbyA unit and also the other SW decoder (I am not competing with other -- dont need to do so.)  The biggest difference betwen my decoder and a real DolbyA is a smoother/cleaner MF/HF, but close to the same response.  The 'other' SW decoder doesn't sound like a DolbyA AT ALL, but is better than nothing.*  The gain curves between a real DolbyA and my SW decoder are almost IDENTICAL (within about 0.25dB most of the time, and 0.5dB error once in a while.)  The curve shapes are indeed the same (it took high order polynomials to get it that accurate.)  ALSO, we didn't just compare against one unit, but multiple units -- and the person doing the comparison uses DolbyA and DolbySR almost daily.  In fact, we are probably going to start on an SR project, even though less SR material appears to be leaking out.

  *In my work, I found that emulating the filters on the cat22 was futile, and probably what the 'other' SW decoder did -- I designed the filters based on another concept (keeping it secret), and it works wonderfully.  The cat22 filters (or an adhoc filter bank) tend to sound like the other SW decoder and not a real DolbyA.

The lack of tone is a definite issue, but I have found that approx 3/4 or more of the material has a required DolbyA threshold within 1 or 2 dB.  It is easy to seek out the best level (usually takes me 2-3 tries to get within 0.25dB -- which is generally close enough.)  Also, if there is a tone, it is just an offset from a displayed level to calculate the necessary threshold (problem solved.)
Most of the online/CD material seems to require a threshold (defined by my software) of -14dB +- 1.5dB or so.  There are a few out-liers which require very different thresholds.  One recording that I have confounds me by requiring a -7.5dB threshold, but almost all others are in the -14dB range.  Usually, within the same album, the thresholds are the same.

Almost always, 0.25dB error is close enough, and most material works well with 0.50dB error.  Music that seems to require very close setting would be things that sound like the master copy of UnderAttack from ABBA.  Also, Band on the Run is also a little bit picky in the pauses at the beginning of the song.   Gotta get those tricky time constants correct (and a simple attack/release time constant WILL NOT WORK CORRECTLY!!!)

Of course, for professional purposes, you really do want to get within 0.25dB, but for causal listening practically all of the advantage can be had with an error of 0.5dB.

The way that I have found to use the decoder is to grab my on-computer archives and decode them (producing CD or memory stick for later use).  In some cases, it is very desirable to run some finalizing on the material (after decoding, ABBA needs a little compression/limiting to sound correct.)  However, my DolbyA copies of ABBA do sound NICE when properly decoded.  In the specific case of my ABBA recordings, almost all of them are not usefully DolbyA encoded, but I do have one which was obviously not finalized -- and fortunately (for me) left the DolbyA on as the normal dynamic range control. 

As I have claimed -- just because I have a certain tool, it doesn't mean that I believe that the tool is useful for everything.  It is just that it is useful (whichever DolbyA decoder you use -- a real DolbyA or my SW) in more cases than most people might realize!!!

5
Support - (fb2k) / Re: Many pops and other noise when converting MP3 Files for use in car w/ Compressor
Last post by Simon_ Thunder -
I am having problems finding a good solution to convert my MP3's and FLACs for use in my car. I have tried various compressors and limiters. The two most recent ones I have used George Yohng's W1 Limiter and GComp (both use the George Yohng VST Wrapper, have produced lost of nasty pops after conversion.

My immediate assumption was that the conversion stream was clipping. But I tried out several songs using the compressors and got clean sound in both occasions before I started the conversion.

Is there a way to handle this issue in foobar? I'm using the latest stable version but not the beta.
Use the Foobar2000 VST 2.4 adapter by Yegor Petrov and not George Yohng VST Wrapper.
George Yohng VST Wrapper in some cases not stable.
Foobar2000 VST 2.4 adapter by Yegor Petrov - https://hydrogenaud.io/index.php/topic,84947.0.html
Try this one vst!
> Jeroen Breebaart :   Broadcast  - http://www.vst4free.com/free_vst.php?id=548
Select settings - smooth or agc mode
6
Scientific Discussion / Re: Have a working 'expander' based on DolbyA (not same design) -- works well.
Last post by krabapple -
Your terminology is slightly confusing.  It's not surprising for a studio tape since 1965 have been Dolby A encoded; it is surprising for it not to have been decoded for commercial release .  So your concern is really 'Dolby A encoded stuff released without decoding'.

AFAIK, Dolby A decoding was not available on any consumer playback gear (e.g reel to reel decks).  So no Dolby A 2TRK tapes would have been released commercially, unless it was by mistake.  Yet you say you have  "a 2TRK copy, unprocessed and is a DolbyA master of ABBA Gold and MORE ABBA Gold."    What gives you absolute certainty that these tapes are what you say? 

Given all the adjustments to EQ and dynamic range available to CD mastering engineers, I just don't see how you can be certain that commercial releases are suffering from Dolby A nondecoding, versus normal mastering choices.   Tipped up treble is hardly rare in CD masterings, and neither is compression, and both are easily achieved without Dolby NR playing a role.

Yet you go on to claim:
Quote
Believe it or not, often the better quality disks tend to leave the DolbyA undecoded -- it is the horridly misprocessed material that isn't usefully DolbyA encoded.

I don't see how you can *know* this.

However, you also say you have 'PROVABLY' Dolby A encoded material . If that is so, then you can do the comparison I mentioned previously  (decode with a Dolby A hardware decoder vs your software).

But there's also the whole issue of the Dolby calibration tone, which would only be printed to the master tapes;  without that, setting levels for decoded playback, is guesswork....



8
Audio Hardware / Re: Subwoofer advice needed
Last post by Fairy -
I'm setting up my sub. You can even select your main speakers if they are B&W.

I found out that with Phase 0, the sub seems to cancel out the main speakers and with 180 degrees they work together.

How is this possible when the speakers are lined up perfectly next to each other?
My speakers are not out of phase, + to +, - to -.

I have exactly 30 minutes of experience with subs so bare with me :)
9
Scientific Discussion / Re: Audio Summing Algorithm
Last post by jsdyson -
If I get up the energy to play with this stuff, I can probably put together a rough 'FFT' based summer (that is, not an FFT, but power based) to see what forcing the phases to match would sound like.  I suspect the results would at least be grainy sounding (like some of the ABBA recordings due to the abuse of the quadrature/destroying the analytical nature of the signal), but more than likely renders the sound unintelligible.

Actually, I have done something similar before -- by zeroing the phase of a given FFT (magnitudes the same, phase is zeroed -- all the same), and the result was pretty much unintelligble-- it was possible to detect some of the material, but didn't seem to be useful.
Can you send us some samples, please? And why does it happen?
I have massive archives from when I played with that stuff (about 2013 or so), and will look for something to demo to you.   Like I wrote earlier, there was little benefit even with the compressor/expander thing to work in the Fourier domain (more trouble than it was worth, even though I wanted to work in multiple bands -- seems like the transform would give you lots of bands and seems like that would be good -- but it wasn't all that helpful.)  I could definitely compress the hell out of the signal, but I didn't like the sound of a 512 band compressor. :-).   It seems like 6-8bands is into the diminishing returns, and it seems helpful to try to keep the 500-2500Hz range in one band by itself -- various reasons for that.

John
10
Scientific Discussion / Re: Have a working 'expander' based on DolbyA (not same design) -- works well.
Last post by jsdyson -
Regarding my disgust as to the quality of some of the available recordings, and finding that they were like left with DolbyA encoding intact -- yes. 


So,  even though Dolby A was commonly used professionally from the mid 1960s through the rest of the analog era, either it was not noted down on many tape boxes, or the CD transfer/mastering engineers failed to notice , or simply ignored, the Dolby A indication on the tape box?

I have heard of cases of the former (Dolby used, but not indicated on the tape box) but I'd be surprised to find such cases were as widespread as you imply. 





I am truly NOT meaning to misinform, and also I know that I am not crazy (at least, probably not), but it is really interesting that I am running into a lot of DolbyA encoded stuff.

Firstly, DolbyA encoding isn't 'fatal', and some people might like the hard, over compressed HF sound.
Secondly, I was SUPER surprised, and started doubting my sanity until I got help from a recording engineer -- and have PROVABLY DolbyA encoded material.  The effect of decoding that provable DolbyA material is similar to the decoding of some popular materials.

My online demos are NOT fakes, and they are NOT contrived in any way.  Most of my stuff is now on digital media, but I still have some CDs that I can grab, decode and demonstrate the proper effects of the decoding.  I have one example on my repository that I mentioned before (and here it is again), the song is 'Bicycle', and the repo is: https://spaces.hightail.com/space/z3H68lAgmJ
(The nasty sound that I hear on Bicycle -- before cleaning up with DolbyA decoding is similar to what I hear on a lot of disks (not all of them.)  Believe it or not, often the better quality disks tend to leave the DolbyA undecoded -- it is the horridly misprocessed material that isn't usefully DolbyA encoded.

I just found my Queen CD -- it is 99.9999% determined to be DolbyA encoded: 
Queen Greatest hits:  Copyright (C) 1992 Hollywood Records, ID 61265-2,

On the other hand, I have an ABBA CD that is all compressed to hell -- I know that because I also have a 2TRK copy, unprocessed and is a DolbyA master of ABBA Gold and MORE ABBA Gold.   The all compressed to hell CD (not plausibly DolbyA encoded):
ABBA Gold, 40th Anniversary Edition, Copyright (C) 2014 Polar Music, the ID code is long and unimportant since I don't claim that it is DolbyA encoded.

YES -- there are both DolbyA and non-DolbyA recordings available on CDs and online -- but, I suspect that some percentage of the 'too much treble' or 'harsh sound' complaints from people MIGHT be because of undecoded DolbyA.

I have only made passive mention about this revelation until now -- it seems like people tend not to be interested, because THEY JUST DON"T SEEM TO BELIEVE IT.

LISTEN to the examples...  If YOU have some material that sounds DolbyA encoded (too much HF, too compressed, but not DolbyB), then send me a snippet, and I can decode and send it back.   It might be easier if you just run my DolbyA decoder on your (relatively recent) PC -- IT REALLY WORKS!!!

However, there are indeed cases where the DolbyA decoder appears to work (almost), but the material is NOT DolbyA encoded.  Likewise, very often if you try to decode non-DolbyA encoded material, it sounds like cr*p.

SO -- there are two things that should happen (for the sake of audiophile and/or simple recording quality):  people should have access to DolbyA compatible decoders, or the record distributors should spend the several hours per release to just decode the material.

One idea came to mind -- leaving DolbyA encoding on a recording is kind of a very nasty form of mastering -- it brightens up the recording and does a bit of dynamic range restriction (on the low level side.)   In this case, that is just being cheap.

Too much of my music material has been changed from harsh sounding cr*p into near audiophile quality.

John
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