File-based audio playback - compressed vs. uncompressed

[StanleyB]

Stan, can you recollect the equipment used and how it was coupled when you noted these differences? I presume you used your own DAC when you discovered this?
It may or may not be related, but it may help flesh out the circumstance to further isolate the cause.

I am having to refrain from comments at this moment in time. Clive mentioned something of significant commercial importance that needs further investigation.

As I mentioned before, I was not using USB. I mainly use optical or coax. The speakers are the NS1000M. DACs were varied, but not necessarily available on a commercial basis. Some are prototypes.

[ZebuTheOxen]

Why not compare the digital output of all these files? Once post-decoder and once at the output stage?
Inverting signal A and removing it from signal B, and vice versa will give you absolute differences across the entire spectrum being transferred, if there are any.

[bobbasrah]

I am having to refrain from comments at this moment in time. Clive mentioned something of significant commercial importance that needs further investigation.

As I mentioned before, I was not using USB. I mainly use optical or coax. The speakers are the NS1000M. DACs were varied, but not necessarily available on a commercial basis. Some are prototypes.

Ok, presumably in due course, the investigations of the lads will narrow down the suspects. The considerations are certainly wide ranging.

For the moment we can ascribe the difference noted in your own case between FLAC and WAV to be relate NOT to USB for certain, and using DACs which may or may not be in the marketplace, some of which may have been prototypes.
Did Andre not have similar experience presumably in less experimental circumstances? I wonder if there is a commonality?

[StanleyB]

Did Andre not have similar experience presumably in less experimental circumstances? I wonder if there is a commonality?

I think that some of the more modern DAC chipsets are far better in detecting even minute differences in the audio signal. The compression/decompression process that a FLAC file experiences is probably leaving behind artefacts that are affecting the sound. Less detailed digital to analogue conversions are incapable of noticing these minute differences. I reckon that is why so few people have been able to notice the difference.
I compared the APE audio format against the FLAC and WAV ones. No problem with APE. So it is without any shadow of a doubt an issue solely related to FLAC and no other lossless format. But only the low jitter receiver chips seem to be able to pick out the problem. The common (and higher jitter) SC8416 fails to resolve the difference, whilst the superior low jitter WM8804/5 is far better at it.
But note that these are just my test results. Other DAC designers/testers/owners who have access to DACs with differing receiver chips might be able and willing to disclose their test results in due course.

[dave2010]

I think that some of the more modern DAC chipsets are far better in detecting even minute differences in the audio signal. The compression/decompression process that a FLAC file experiences is probably leaving behind artefacts that are affecting the sound. Less detailed digital to analogue conversions are incapable of noticing these minute differences. I reckon that is why so few people have been able to notice the difference.
I compared the APE audio format against the FLAC and WAV ones. No problem with APE. So it is without any shadow of a doubt an issue solely related to FLAC and no other lossless format. But only the low jitter receiver chips seem to be able to pick out the problem. The common (and higher jitter) SC8416 fails to resolve the difference, whilst the superior low jitter WM8804/5 is far better at it.
But note that these are just my test results. Other DAC designers/testers/owners who have access to DACs with differing receiver chips might be able and willing to disclose their test results in due course.

I've followed this with some interest. Firstly, assuming FLAC is working properly, there is absolutely no loss of data, and a round trip of the form:

File1 -> FLAC compression -> FLAC decompression -> File2

should show that the data in File1 is EXACTLY equal to File2.
If this is not the case, then there is a problem with the compression or decompression process.

There is nothing approximate about lossless compression/decompression.

It is the case that some lossless methods may make use of a lossy component, which in the case of audio could be mp3 or aac. Essentially they do something roughly equivalent to a round trip compression/decompression cycle, and then subtract the result from the input to give a residual. The residual is then compressed and then stored and/or transmitted.

Various techniques are used for the digital encoding, such as run length encoding and Huffman encoding, both of which are not lossy.

It is claimed that FLAC files sound different from, for example, WAVs. This could be due to problems in implementation in either FLAC or WAV playback.
If the claim is that FLAC files sound worse than equivalent WAV, then clearly WAV is being used as the reference, and preferred. It does not automatically follow that a difference in perceived sound implies one is better than the other. Let's assume for the moment that FLAC does sound inferior.

With either format, the data is converted ultimately to a data stream which is fed into a DAC. If both FLAC and WAV based systems are working properly, the data stream to the DAC should be identical.

Ways in which they may then sound different should then only be due to timing issues, or possibly corruption in the data. Corruption is unlikely under normal circumstances. If the data is buffered sufficiently just before the DAC, there should be no difference. Note though that if there is any data corruption in compressed format data, that the audible effects could be worse (though not necessarily so) compared with similar corruption in other formats, because it is possible that data corruption in compressed data could lead to error propagation effects. This kind of situation can arise in video encoding/decoding in, for example, MPEG, where if the I frames are corrupted, the errors will propagate through frames up to the next I frame.

It does not follow that such corruption in compressed audio streams will always lead to significantly worse sounding output, as it's possible that the corruption is in part of the signal which has little perceptual effect. In both audio and video encoding and transmission, it is now common to protect parts of the encoded data which are more likely to have a damaging effect if they are corrupted to a higher degree of protection than other components.

[AlexM]

Stan,

Here is an experiment maybe you can try.

Looking at the datasheets of some of the reciever chips, most seem to have a pin that is used to indicate sync problems with the SPDIF frames. typically these are used to light an LED when there is a sync issue.

It would be interesting to connect this output to a counter and play music in wav and flac formats, and see if there is any difference caused by either jitter ourside of the reciever's tolerance or problems with the electrical interface.

Sync is usually locked by successful reception of the preamble bits in an SPDIF frame, and is unlikely to error during reception of the rest of the frame (although not impossible).

Cheers,
A.

[bobbasrah]

I think that some of the more modern DAC chipsets are far better in detecting even minute differences in the audio signal. The compression/decompression process that a FLAC file experiences is probably leaving behind artefacts that are affecting the sound. Less detailed digital to analogue conversions are incapable of noticing these minute differences. I reckon that is why so few people have been able to notice the difference.
I compared the APE audio format against the FLAC and WAV ones. No problem with APE. So it is without any shadow of a doubt an issue solely related to FLAC and no other lossless format. But only the low jitter receiver chips seem to be able to pick out the problem. The common (and higher jitter) SC8416 fails to resolve the difference, whilst the superior low jitter WM8804/5 is far better at it.
But note that these are just my test results. Other DAC designers/testers/owners who have access to DACs with differing receiver chips might be able and willing to disclose their test results in due course.

Stan, I think you can agree that if I can send 24/192 with no detectable difference between FLAC and WAV, the SPDIF receiver is doing it's job in passing forward that 24/192 to the DAC. If lesser SPDIF receivers cannot cope with the datastream that is another matter, but this is not the case.

Where you said “ Less detailed digital to analogue conversions are incapable of noticing these minute differences”, that was already investigated as I said previously on my mate's esoteric DAC (less than 1 year old), where no differences were noted either. I know his DAC is very serious money Stan, and is as far removed from being “Less detailed digital to analogue conversion” as can be. It is equally unlikley to contain a “common” SPDIF receiver.

As an aside to the assertion however, if a “superior”SPDIF” receiver such as you cite, lets through something other than the 24/192 datastream, I would seriously question whether that is an advance, irrespective of where the problem arose.

Out of curiosity, which media player were you using for these tests?

[StanleyB]

As an aside to the assertion however, if a “superior”SPDIF” receiver such as you cite, lets through something other than the 24/192 datastream, I would seriously question whether that is an advance, irrespective of where the problem arose.

well if you think I am mental or completely wrong then there is no purpose in me continuing with this discussion .

[bobbasrah]

well if you think I am mental or completely wrong then there is no purpose in me continuing with this discussion .

No Stan I do not think you are mental, nor inferred it, what I referred to was that is the advanced receiver such an advance if it lets through what is not intended, whereas the previous generation did not, yet fulfilled it's technical purpose?.

[synsei]

Perhaps your ears aren't flapping at the right speed Bob, try upping the frequency to 128 flaps per second, that should get you sorted...