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In Reply to: Not quite posted by audioengr on November 14, 2006 at 10:24:55:
Two points: 1) The PCM 1704 is a D/A converter not an A/D converter. 2) Also the DF 1704 is an 8 x OVERsampler not an UPsampler (ie. it is synchronous not assynchronous).Where is your justification that this 24 bit converter is automatically better than the PCM63K? Surely not just the number of bits. I agree with you that the 1704 is a great DAC chip but so is the 63.
My understanding is that the major reason they stuck with the older DAC chip is that it has a more robust current output, which makes means they can use passive I/V conversion and a tube output stage without needing a low noise opamp to boost the signal. Apparently, the 1704 has a quite low current output that is not as suitable for passive conversion or for use with tubes. Monarchy actually offers an "upgrade" to the PCM 1704 for their DACs. I inquired into it for my DAC and they advised me not to do it because the analog stage in the M24 is optimized for use with the PCM63. Monarchies older DACs, which use an ultra high speed opamp for I/V conversion will accept the upgrade with no problems.
Follow Ups:
"2) Also the DF 1704 is an 8 x OVERsampler not an UPsampler (ie. it is synchronous not assynchronous)."Although commonly used in this context, the terms are often interchanged. Wadia, for example, calls its synchronous oversampling "upsampling".
So what I said then is generally correct, is it not?
Okay, lets split hairs:PCM 1704 has 4 dB more dynamic range. I just has more resolution with 24 bits versus 20. The THD+N is 102 dB for the 1704 and 100 dB for the 63.
The difference in output current is +/- 2ma versus 1.2ma for the PCM1704, so this can be helpful, but it's still a small current IMO. This is the only positive with the 63 IMO.
The reality is that most designs including this one are not resolving enough for you to hear -100 dB anyway. They need a lot of mods to get there IMO.
"I just has more resolution with 24 bits versus 20."The only condition where wordlength affects resolution is if the input data is of higher wordlength (DVD-A) than the lesser DAC's max wordlength. Although in such cases, it would be more-accurate to say the 20-bit DAC loses resolution. (And most of the losses in 24 bits vs. 20 would be in the form of noise.)
For Redbook CD playback, all else being equal, a 24-bit DAC may sound slightly cleaner than the 20-bit DAC (due to more-precise interpolation), but the resolution would be almost identical. For the extra bits in CD playback are used solely for digital filtering.
I listen to a lot of native 24-bit music mastered from tape as well as upsampled 16-bit data using SRC. Seems to me that a 24-bit DAC would take advantage of this.
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