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Topic: How to determine my mobo S/PDIF output's true sample rate? (Read 6543 times) previous topic - next topic
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How to determine my mobo S/PDIF output's true sample rate?

Hi there.

My PC has a Realtek ALC850 chipset and an electrical S/PDIF output. I feed this mostly 16/44.1 going on to an external DAC, which does not indicate the sample rate it's receiving. I have no idea whether the mobo is resampling the digital output to 48KHz -- some threads say it does, some say it doesn't, nobody seems authoritative.

For a few days I have the use of a M-Audio Fasttrack Pro, which is a USB soundcard (soundbox?) with S/PDIF in. It struck me that I might find the answer by playing some music through the mobo S/PDIF out to the M-Audio S/PDIF input, recording it, and seeing what sample rate I get. The trouble is that every single piece of software I can find has the user set a sample rate, and (presumably) resamples to that rate. Nothing seems to just spool the data from the socket to a file.

I wonder can anyone suggest some free/demo software that would do what I need, i.e. determine the sample rate that's coming into the M-Audio S/PDIF socket?

Or for that matter, another way to definitively find out what my mobo outputs?

How to determine my mobo S/PDIF output's true sample rate?

Reply #1 –
Quote from: Morte on
Hi there.

My PC has a Realtek ALC850 chipset and an electrical S/PDIF output. I feed this mostly 16/44.1 going on to an external DAC, which does not indicate the sample rate it's receiving. I have no idea whether the mobo is resampling the digital output to 48KHz -- some threads say it does, some say it doesn't, nobody seems authoritative.

For a few days I have the use of a M-Audio Fasttrack Pro, which is a USB soundcard (soundbox?) with S/PDIF in. It struck me that I might find the answer by playing some music through the mobo S/PDIF out to the M-Audio S/PDIF input, recording it, and seeing what sample rate I get. The trouble is that every single piece of software I can find has the user set a sample rate, and (presumably) resamples to that rate. Nothing seems to just spool the data from the socket to a file.

I wonder can anyone suggest some free/demo software that would do what I need, i.e. determine the sample rate that's coming into the M-Audio S/PDIF socket?

Or for that matter, another way to definitively find out what my mobo outputs?


ALC850 will sample-rate 48 kHz as it is AC97.
New HD Sound codecs won't. Like Realtek 88x series.

To find it out? Borrow a receiver/DAC which shows it 
Or go to friends house with your rig who has receiver/DAC which shows it 

How to determine my mobo S/PDIF output's true sample rate?

Reply #2 –
The analogue output resamples per AC97 spec, but the does the digital?

The documents say it doesn't resample on electrical S/PDIF but does on TOSLINK. Some people on these forums say it does resample on electrical S/PDIF and the docs are wrong, some say it doesn't, and nobody says how they "know". I'd like to get a definitive answer once and for all.

Quote
To find it out? Borrow a receiver/DAC which shows it smile.gif
Or go to friends house with your rig who has receiver/DAC which shows it biggrin.gif


I don't know anybody with the right gear. Though I'll keep an eye open...

How to determine my mobo S/PDIF output's true sample rate?

Reply #3 –
S/PDIF is simply a method of transmitting digital data between one place and another. When resampling occurs it is before the data is input to the S/PDIF sending process or after the data comes out of the S/PDIF receiving process. Working properly, S/PDIF transmission is identical to sending audio data with any other correctly working hardware, such as over ethernet or copying from one hard drive to another.

A recording program, where you must set the sample rate for the S/PDIF input, never resamples. That sample rate setting only applies to the control information for the output file. If you don't set it to the same sample rate as the incoming audio data, the recorded file will play back either too fast or to slowly. It can be corrected later by changing the control information in the file.

If you have a real audio card that can handle audio data without resampling, you can make a test by sending audio via S/PDIF from the suspect card, receiving it via the trusted card, and recording it as the sample rate it is supposed to be. If playback sound right, neither too fast or too slow, the data was not resampled before transmission.

You can further test by copying the recorded file back to the original computer (or vise versa) by some other means, say ethernet or by writing on some portable media as data. Once both files are on the same computer, use an audio editor or utility to check that the files are identical, bit for bit. Of course you have to account for any bit of silence you may have recorded before the beginning or after the end of the transmitted data.

As far as testing playback speed goes, you need to set the receiving soundcard back to its internal clock first. During the S/PDIF copy process, the receiving device must use the sending device’s clock . Without first setting back to its own internal clock, it will still be using that external clock for playback.

How to determine my mobo S/PDIF output's true sample rate?

Reply #4 –
Quote from: AndyH-ha on
S/PDIF is simply a method of transmitting digital data between one place and another.


Ah, I made the (with hindsight silly) assumption that it flagged the data as having a certain sample rate, and the recording software would convert as required. I don't know quite how I came up with that.

Quote
If you have a real audio card that can handle audio data without resampling, you can make a test by sending audio via S/PDIF from the suspect card, receiving it via the trusted card, and recording it as the sample rate it is supposed to be. If playback sound right, neither too fast or too slow, the data was not resampled before transmission.


Thanks Andy, that did the trick.

I played a 44.1 file over the ALC850 electrical S/PDIF output, and recorded it over the M-Audio S/PDIF input flagged as 44.1 with Audigy. When I played back the capture, it was slow. I re-flagged it as 48 and it played back at the right speed. [On a close comparison it sounds slightly worse than the original, not quite as "tight".]

So the mobo ALC850 is resampling 44.1 to 48 before it sends it to the electrical S/PDIF output. After a week of headscratching, I finally know for sure.

Thanks again, folks.

How to determine my mobo S/PDIF output's true sample rate?

Reply #5 –
Yes the Realtek ALC850 does resample to 48 KHz. The best & easiest way to test is ....Get a DTS 5.1 Audio CD and play it. If you hear perfect sound from your reciever (which is connected via Coax or Toslink to your PC) then resampling does not occur. If you hear the song in a garbled way with noise (this is not static btw) then its resampling to 48KHz.

How to determine my mobo S/PDIF output's true sample rate?

Reply #7 –
You are talking about DVDs, are you not. An audio CD by definition can only be red book stereo, and that is all a CD player (as distinguished from a multi-player) will play.

How to determine my mobo S/PDIF output's true sample rate?

Reply #8 –
He's talking about dts files wrapped in wav, so called DTS-WAVs which can be burnt to red book cd. But if played in a regular CD player, you get noise.
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How to determine my mobo S/PDIF output's true sample rate?

Reply #9 –
They can be written on a CD-R, but it will not be red book, not an "audio CD."

How to determine my mobo S/PDIF output's true sample rate?

Reply #10 –
Quote
From Wikipedia, the free encyclopedia

The DTS-CD, DTS Audio CD or 5.1 Music Disc (official name) is an audio Compact Disc that contains music in surround sound format. It is a predecessor of DVD Audio. Physically, it conforms to the Red Book standard, except for the way the music is encoded on the CD. Where regular CDs store the music as linear PCM, the DTS-CD stores music using the DTS format, with the same fixed bitrate as 16-bit linear PCM, namely 1,411,200 bits/s or roughly 1,378 Kib/s.

As opposed to other surround formats, such as SACD and DVD audio, which require a specialized player, a DTS-CD is compatible with most standard CD players with a digital (S/PDIF) output. CD (and DVD) players recognize the disk as a standard audio CD. The only requirement is a receiver that can decode DTS audio.
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How to determine my mobo S/PDIF output's true sample rate?

Reply #11 –
Ok, even technical terms don’t have very specific meanings any more. Just rip it to your speakers and see if you like its groove.