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Are all DACs the same - an investigation

Nessuno

Member
THD figures

THD figures

By the way: it would be interesting to know the THD figure of the DAC that caused the issue, which is normally between the specs published by the manufacturer or between the measures done by reviewers in more tech-wised audio magazines.

All in all, what Alan Shaw perceived and then measured is harmonic distortion at 1kHz, isn't it?

{Moderator's comment: it was tones he fed to the DAC at 440Hz and alternatively 1kHz. It did not seem to matter what signal level these were at (0db or -10dB), the distortion remained relatively the same.
 

Nessuno

Member
Hiding the objective truth?

Hiding the objective truth?

By the way: it would be interesting to know the THD figure of the DAC that caused the issue, which is normally between the specs published by the manufacturer or between the measures done by reviewers in more tech-wised audio magazines.

All in all, what Alan Shaw perceived and then measured is harmonic distortion at 1kHz, isn't it?

{Moderator's comment: it was tones he fed to the DAC at 440Hz and alternatively 1kHz. It did not seem to matter what signal level these were at (0db or -10dB), the distortion remained relatively the same.
Just to clarify my question: THD, normally defined as the ratio between (the root mean square values of) a singe frequency input tone (typically 1kHz) and its harmonics present in the output, is a figure normally presented in the published specifications of a device and can give a rough idea of what to expect from it in terms of signal distortion.

Then, if a certain distortion is audible, likeable or desirable could even become a matter to debate, but if the designer or the enthusiastic reviewers don't give this value to possible customers to begin with, maybe they know they've got something to hide... maybe...
 
A point of view - a test strategy proposal?

A point of view - a test strategy proposal?

http://cdn.shopify.com/s/files/1/0321/7609/files/caig.pdf?264

The above is a link to a white paper by Benchmark Media on how to achieve a clean setup in an audio chain.

Within it is a very interesting suggestion regarding how to test for distortion in a simple manner, but with a twist not covered previously.

"9.2 Distortion Testing

Once you are satisfied with the frequency response, noise floor, and transient response of your system, it is well to do some overall distortion measurements. While low frequency total harmonic distortion measurements have merit, in bandwidth limited systems, high frequency THD measurements are almost meaningless. The filters in an A to D converter or stereo generator do a nice job in removing the distortion products of anything above 10 kHz and destroy the accuracy of any measurements much above 2 kHz; hence everything may measure better than it actually is. If slewing induced intermodulation and/or transient intermodulation distortion exist within the system, it will only occur at the higher frequencies. The best way in a bandwidth limited system to detect their presence is with the CCIF twin tone IM distortion measurement.

By using 14 and 15 kHz tones mixed 1:1, a 1 kHz IM product is easily detected if SID/TIM exists in an FM broadcast system. A 19 and 20 kHz pair may be used to evaluate A to D converters or other equipment in the audio chain. We believe that every broadcast facility should perform twin tone IM distortion measurements to see the truth about their high frequency audio performance."

I cannot vouch for the accuracy of what this paper says, if only because I lack electronic engineering chops; but perhaps someone else can comment on this if what these people are saying looks reasonable.
 

witwald

Active member
Examples of TIM measurements using 19kHz+20kHz test tones

Examples of TIM measurements using 19kHz+20kHz test tones

By using 14 and 15 kHz tones mixed 1:1, a 1 kHz IM product is easily detected if SID/TIM exists in an FM broadcast system. A 19 and 20 kHz pair may be used to evaluate A to D converters or other equipment in the audio chain. We believe that every broadcast facility should perform twin tone IM distortion measurements to see the truth about their high frequency audio performance.
The above approach appears to be a well-known test method, which is often used to supplement the usual THD measurements. Here are some examples of CD players that were measured for their TIM performance using a 19 kHz and 20 kHz pair of test tones. These were reported in past issues of Stereophile magazine. Some players do better than others, and in some cases the 1 kHz distortion product is quite visible (although still at a low level)

Classé cdp-202 CD/DVD player measurements

TIM Results:
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Musical Fidelity kW DM25 CD transport & D/A converter measurements

TIM Results:
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Linn Majik CD player measurements

TIM Results:
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Sony CDP-XA7ES CD player measurements

TIM Results:
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Audio Research Reference CD9 CD player/DAC measurements (2013)

TIM Results:
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Marantz CD5004 CD player measurements (2011)

TIM Results:
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Quad 99 CDP-2 CD player measurements

TIM Results:
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