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Develop a metric for CD Transport and CD Player performance

73hadd

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Inpsired by the 9% variance from best-to-worst in CD Rip accuracy between different CD ROM drives shown here. https://forum.dbpoweramp.com/showthread.php?43786-CD-Drive-Accuracy-2019

Use case #1

Compare transports to transports with accuracy % metric.

Use digital output (SPDIF/Toslink) from multiple optical disk transport devices such as CD Transports, DVD Players, or CD Players.
The % accuracy number from each device to be captured in a table. Observe if there is a variance between devices.


CD Transport test method

1. Using a reference music CD on a computer, create a ripped .wav and verify it is a known good copy (using something like AccurateRip.)
2. Use the same reference music CD in one test device. Capture digital output to .wav.
3. Use @pkane 's software DeltaWave to compare the reference .wav to the .wav created by the device, specifically the CLI comparison with % matched output: https://www.audiosciencereview.com/...ve-null-comparison-software.6633/post-1117064
4. Repeat test for multiple devices and store data in a table.

End use case #1


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


Use case #2

Unrelated to the above, compare CD Players to CD Players with accuracy % metric.

Use analog output from multiple CD Players, captured to .wav and compared to reference .wav.
The % accuracy number from each device to be captured in a table. Observe if there is a variance between devices. It is widely accepted that due to variances in DAC and analog output implementation that the results will vary.

CD Player test method

1. Using a reference music CD on a computer, create a ripped .wav and verify it is a known good copy (using something like AccurateRip.)
2. Use the same reference music CD in one test device. CD Player DAC output to ADC interface to capture .wav
3. Use @pkane 's software DeltaWave to compare the reference .wav to the .wav created by the device, specifically the CLI comparison with % matched output: https://www.audiosciencereview.com/...ve-null-comparison-software.6633/post-1117064
4. Repeat test for multiple devices and store data in a table.

End use case #2

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


This should ignore audibility for now and focus on "Device A created a more accurate replication than Device B."
 
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pma

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Test file burnt to disc and then ripped, the files are bit-perfect identical. PKmetrics below -300dB. I can start testing ;).

testfile_vs_rip.png
 

Blumlein 88

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CD transports put out bit perfect signals. No need to test. I've done that testing. Many recording interfaces let you feed the SPDIF signal in and record it.

CD players will test more or less like dacs. With various results.
 

pma

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CD players will test more or less like dacs. With various results.

Unfortunately, the method does not work with CD players. The difference in rotation speed and thus resulting frequency makes Deltawave unable to work. With 1kHz dithered as an original signal, I get the stagecoach-wheel effect. From the player I get 999.84Hz. Funny.
 
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pma

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OK. The best method was to use scientific notch filter tuned 999-1001Hz in Adobe Audition on the whole 3 minute record. After cutting the file beginning (filter transient response) there is nothing left but dither and very low distortion residuals. So nothing under the sun, no problems in 3 minute record of dithered 1kHz. The amplitude is close to 0dBFS.

Here is a part of the notched file. It remains the same over the whole file. The Y-axis shows an error in samples. As said, TPD dither + distortion. No violent error jumps.

CD_error.png
 

Blumlein 88

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Unfortunately, the method does not work with CD players. The difference in rotation speed and thus resulting frequency makes Deltawave unable to work. With 1kHz dithered as an original signal, I get the stagecoach-wheel effect. From the player I get 999.84Hz. Funny.
So is the speed variable because Dwave can easily handle a fixed speed difference you are describing? Can you post results from Dwave? Try using music first. Dwave works better with music than with test signals.
 

Berwhale

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73hadd

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CD transports put out bit perfect signals. No need to test. I've done that testing. Many recording interfaces let you feed the SPDIF signal in and record it.

CD players will test more or less like dacs. With various results.
CD Transports - I do appreciate that point of view and have heard it many times before, but I haven't seen the evidence. It's really hard for me to believe they are all the same considering the wide variety of SPDIF implementations for example. Some of us are weird and like to use our old DACs that do not clean up jitter like the new DACs do. Do you have documents on your Transport testing, how many DUTs were compared etc?

CD Players - Agreed they will vary. As seen on the Marantz SA-10 thread, people will keep asking "Why buy a $7500 cd player when a $50 dvd player does the exact same thing." Which is of course:
1. The Rolex vs. Timex. Paying for level of effort in the build and materials for a comparable output
2. If the more "quality" player actually renders a more accurate replica of data on the disc, even if not audible, it is at least a metric to say DUT A measures better than DUT B. I was going to say "more expensive" but we have too many examples of where components and implementation are not proportional to cost.
 
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73hadd

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Isn't this test basically pointless? We've known how to do audibly transparent transports for a few decades now.

We can probably define these concepts better than I will outline here, but in the spirit of ASR, measurements are valuable.

Subjective - "This device sounds better to me." Only way to prove is DBT.
Objective - "DUT A measures better than DUT B." Need data.
Pseudo-Objective - "You can't hear the difference." Also needs DBT?
 

MRC01

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It may be worth measuring how a transport implements SPDIF output. For example, what happens to the data stream when you pause, stop, fast forward, etc. Does it send empty frames or stop sending entirely? Maybe the first for a while, then after a timeout, the second? If you hit pause or stop while music is playing, does it send an empty frame following the last music frame?

Does it support DVD-A? SACD? DSD? Pre-emphasis? HDCD? When decoding HDCD does the SPDIF output change to 20 or 24-bit? Does it play gapless across tracks? What happens if the next track has a different sample rate and bit depth?
 

Blumlein 88

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CD Transports - I do appreciate that point of view and have heard it many times before, but I haven't seen the evidence. It's really hard for me to believe they are all the same considering the wide variety of SPDIF implementations for example. Some of us are weird and like to use our old DACs that do not clean up jitter like the new DACs do. Do you have documents on your Transport testing, how many DUTs were compared etc?

CD Players - Agreed they will vary. As seen on the Marantz SA-10 thread, people will keep asking "Why buy a $7500 cd player when a $50 dvd player does the exact same thing." Which is of course:
1. The Rolex vs. Timex. Paying for level of effort in the build and materials for a comparable output
2. If the more "quality" player actually renders a more accurate replica of data on the disc, even if not audible, it is at least a metric to say DUT A measures better than DUT B. I was going to say "more expensive" but we have too many examples of where components and implementation are not proportional to cost.
I don't as most of it was years ago. The bit perfect aspect is very easy. You record the bits and compare with the originals and there is no difference. I of course couldn't test all CD players, but did a few CD players (including a belt drive model, and a Spectral player), a couple DVD/Universal players and one bluray player. One thing I did a couple times was to put a disc on repeat and record the digital out for hours looking for an error. Never got even one error. I don't think anything other than a broken player would have trouble with bit perfect output. Even if jittery as heck the right bits get through. Players did vary in the jitter levels in the output stream. Even older DACs did some work cleaning that up and filtering out the worst of it.

The oddest jitter display is with an old Pioneer universal player. Whenever you started a new track the jitter was huge and slowly ramped down to a nice low number over the 1st 15 seconds. Stereophile tagged it as a player with some of the worst jitter they'd measured. But they only used a 30 second track. So half of it was very high and half was low which averaged out to a very poor result. They didn't catch that. Yet you can't hear a change in sound quality the 15 seconds when jitter is way high on the player. So as with so many things audiophile concerns about jitter are over blown.

I doubt any non-broken transport fails to put out the right bits. You can test the jitter looking at the J-test on the DAC output. A transport should deliver the right sample values at the right time, there isn't anything else they are required to do.
 

Blumlein 88

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It may be worth measuring how a transport implements SPDIF output. For example, what happens to the data stream when you pause, stop, fast forward, etc. Does it send empty frames or stop sending entirely? Maybe the first for a while, then after a timeout, the second? If you hit pause or stop while music is playing, does it send an empty frame following the last music frame?

Does it support DVD-A? SACD? DSD? Pre-emphasis? HDCD? When decoding HDCD does the SPDIF output change to 20 or 24-bit? Does it play gapless across tracks? What happens if the next track has a different sample rate and bit depth?
At one time digital output of DSD or SACD wasn't allowed. SACD even in multi-channel was converted to 20 bit 48 khz. On universal players years back if the next output was a different sample rate it switched in about 2 seconds and went on. Most put out a constant stream of zeroes and maintained a lock in the DAC when not playing though a few acted differently. I've never used one that had gapless playback. Of course which formats are supported varies from device to device. One thing you could add to your list is whether they played CD-Rs, CD-RWs, and same for recordable DVD formats.

Please, CD transports are a solved problem from long ago.
 

MRC01

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Jitter may be an interesting test because SPDIF is a "push" protocol. By this I mean the transport pushes the bytes to the DAC, instead of the DAC pulling them from the transport. This requires the downstream device (the DAC) to adapt to the transport's notion of the clock frequency. This adaptation is not a one-time thing but a continual process as the clock speeds can drift over time.

This means with SPDIF jitter can arise from either side: the transport sending bytes with uneven timing, or the receiving DAC having a not-sufficiently-smooth method to adapt to the transport's clock speed. If the clocks disagree by 1 part in 1 million, that's 1 sample every 23 seconds at 44-16 CD.

By comparison, USB "async" is a pull protocol. The DAC requests the data from the source, so the DAC is entirely responsible for data rate / clock speed. It obviates the need to adapt or sync clocks to each other. I believe this is why Amir sometimes measures more jitter with SPDIF (whether coax or toslink) than with USB.
 
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MRC01

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... I've never used one that had gapless playback. Of course which formats are supported varies from device to device. One thing you could add to your list is whether they played CD-Rs, CD-RWs, and same for recordable DVD formats. ...
I use an Oppo BDP-83 as a universal disc player. Its SPDIF playback is gapless in both CD and DVD-A, so long as the format (sample rate & bit depth) is the same from track to track. It also plays computer-burned CDs, DVDs, DVD-A, and BluRays. It also automatically detects and decodes pre-emphasis and HDCD, if you want it to. It can convert DSD to PCM, or deliver the raw bitstream, your choice. It can also downsample high bit rate recordings to whatever lower rate you want, but I've found audible bugs/artifacts in its downsampling so I avoid that feature.
 
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