Transport Verification

ZenCow · 18th September 2008, 04:24 PM

I am looking for tips in setting up a transport verification system.
What I had in mind was a data acquisition card (preferably Linux based drivers) that could be hooked up to a transport's spdi/f output and create a file which then could be compared to the original source.

phofman · 18th September 2008, 05:27 PM

I did a similar test a year ago. Ripped CD-DA using EAC and modified cdparanoia (raising p->readahead=150 in p_block.c to circumvent the caching problem in cdparanoia). Unmodified cdparanoia rips differed from EAC in hundreds of bytes, modified paranoia tracks were identical in 9 out of 10 runs, 4 bytes in the remaining run.

Recorded CD player SPDIF using aplay with proper parameters to avoid any data conversion. Sound card Audiotrak Prodigy 192, I have a very good experience with any envy24 based card.

Trimmed the wavs manually in audacity to have the same time period to single sample. Not really pleasant work, but you can learn it pretty fast.

Compared the wavs using either audacity, sox (subtracting wavs + effect stat), or modified wavdiff http://www.sommerfee.de/programme.html

My two CD players differed from the rip by a few bytes consistently.

ZenCow · 19th September 2008, 06:09 PM

So using the Prodigy 192, it looks like you were recording the CD Transport's spdif analog, and using aplay to create a WAV file, correct?

Question:
If this is true, do you think it would be possible to use a card with a digital in? In other words, eliminate the need for aplay to sample 44.1KHz and let the card sync up to the spdif stream in the manner in which DAC would? I am thinking (as I have not yet bought the card) that this would be a cleaner and more accurate test, and (possibly) eliminate the need for trimming the WAVs.

Please correct me where I am wrong. Thanks.

phofman · 19th September 2008, 08:19 PM

Recording SPDIF means recording the digital signal from CD player (acting as a transport in this setup). My Prodigy192 has an add-on card with SPDIF input. I do not think you can check digital correctness of a CD player by sampling its analog outputs - there are too many additional factors involved along the signal route.

ZenCow · 19th September 2008, 08:24 PM

OK, then I think we are saying the same thing.

Its just that in your original post you mentioned the Prodigy card, of which I was unfamiliar, so I saw in the specs that it only had analog in and concluded....

I am considering the Audiophile 2496 which has spdif i/o, so hopefully a test is in the works for this weekend.

phofman · 19th September 2008, 08:55 PM

You should be fine with that card. Just a note - do not forget to set the card's internal clock to SPDIF input in alsamixer.

ZenCow · 19th September 2008, 09:00 PM

OK, thanks for your help.

18th September 2008, 04:24 PM	#1
ZenCow diyAudio Member Join Date: Jan 2006 Location: Denver	Transport Verification I am looking for tips in setting up a transport verification system. What I had in mind was a data acquisition card (preferably Linux based drivers) that could be hooked up to a transport's spdi/f output and create a file which then could be compared to the original source.

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18th September 2008, 05:27 PM	#2
phofman diyAudio Member Join Date: Apr 2005 Location: Pilsen	I did a similar test a year ago. Ripped CD-DA using EAC and modified cdparanoia (raising p->readahead=150 in p_block.c to circumvent the caching problem in cdparanoia). Unmodified cdparanoia rips differed from EAC in hundreds of bytes, modified paranoia tracks were identical in 9 out of 10 runs, 4 bytes in the remaining run. Recorded CD player SPDIF using aplay with proper parameters to avoid any data conversion. Sound card Audiotrak Prodigy 192, I have a very good experience with any envy24 based card. Trimmed the wavs manually in audacity to have the same time period to single sample. Not really pleasant work, but you can learn it pretty fast. Compared the wavs using either audacity, sox (subtracting wavs + effect stat), or modified wavdiff http://www.sommerfee.de/programme.html My two CD players differed from the rip by a few bytes consistently.

19th September 2008, 06:09 PM	#3
ZenCow diyAudio Member Join Date: Jan 2006 Location: Denver	So using the Prodigy 192, it looks like you were recording the CD Transport's spdif analog, and using aplay to create a WAV file, correct? Question: If this is true, do you think it would be possible to use a card with a digital in? In other words, eliminate the need for aplay to sample 44.1KHz and let the card sync up to the spdif stream in the manner in which DAC would? I am thinking (as I have not yet bought the card) that this would be a cleaner and more accurate test, and (possibly) eliminate the need for trimming the WAVs. Please correct me where I am wrong. Thanks.

19th September 2008, 08:19 PM	#4
phofman diyAudio Member Join Date: Apr 2005 Location: Pilsen	Recording SPDIF means recording the digital signal from CD player (acting as a transport in this setup). My Prodigy192 has an add-on card with SPDIF input. I do not think you can check digital correctness of a CD player by sampling its analog outputs - there are too many additional factors involved along the signal route.

19th September 2008, 08:24 PM	#5
ZenCow diyAudio Member Join Date: Jan 2006 Location: Denver	OK, then I think we are saying the same thing. Its just that in your original post you mentioned the Prodigy card, of which I was unfamiliar, so I saw in the specs that it only had analog in and concluded.... I am considering the Audiophile 2496 which has spdif i/o, so hopefully a test is in the works for this weekend.

19th September 2008, 08:55 PM	#6
phofman diyAudio Member Join Date: Apr 2005 Location: Pilsen	You should be fine with that card. Just a note - do not forget to set the card's internal clock to SPDIF input in alsamixer.

19th September 2008, 09:00 PM	#7
ZenCow diyAudio Member Join Date: Jan 2006 Location: Denver	OK, thanks for your help.

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