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In Reply to: RE: Thankfully the board in question comes with choice of... posted by Mr_Steady on September 09, 2015 at 19:34:38
It's a NOS DAC. I would never say anything good about a NOS DAC that runs at 44 kHz. These are a defective way of playing back digital audio and do not output the waveform that was originally captured in the digital signal.
The photos show a "perfect" square wave, which is not a correct analog signal that can be encoded in a digital format. This shows the presence of imaging distortion in playback. If you had a waveform for a sine wave at high frequency shown over multiple cycles you would see a wavy envelop caused by beating between the true signal and the image.
The "noise" floor is probably the analog noise floor of the DAC with a silent digital signal. There are no plots of sine waves at varies levels, as would show harmonic distortion, no jitter plots, etc... In addition, there are no plots that show whether (how much) the noise floor varies as a function of the input signals being played.
A proper spec sheet or measurement review would have considerably more information than the two plots on the link you provided. Take a look at any of the Stereophile measurements in DAC reviews for what is missing. It looks like the plots shown here were "cherry picked" to be the best possible ones.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
Yet my Audio-gd R2R dac playing cds sounds extremely good. This again shows to me that measurements seldom relate to how a component sounds to an individual listener
Alan
> " I would never say anything good about a NOS DAC that runs at 44 kHz."
Agree with the 44kHz sample rate, but I need more experience with NOS and ladder dacs. Your opinion is duly noted.
> " The photos show a "perfect" square wave, which is not a correct analog signal that can be encoded in a digital format."
That's something I've never heard anyone say before, but I've thought something along those lines for a long time. That testing a dac's or amplifiers performance using odd order harmonics probably is not the best way to do it.
> " If you had a waveform for a sine wave at high frequency shown over multiple cycles you would see a wavy envelop caused by beating between the true signal and the image."
This sounds like a better way to test dac's and amplifiers. If I ever posted any of this on the SET forum there would be an awful blood (mine) bath.
Today I looked for the resistor tolerance specs in the AD 5791 datasheet, but I couldn't find it. I did find the following;
> "The six MSBs of the 20-bit data-word are decoded to drive 63 switches, E0 to E62. Each of these switches connects one of 63 matched resistors to either the VREFP or VREFN voltage. The remaining 14 bits of the data-word drive the S0 to S13 switched of a 14-bit voltage mode R-2R ladder network."
That sounds to me like it's only 14 bits of R2R not the 20 bits advertised. Am I wrong on this, or is that the standard way?
Thanks.
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Big speakers and little amps blew my mind!
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