Does the PCM63 accept 16 bit input data only?... - diyAudio
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Old 19th April 2010, 12:42 PM   #1
Salar is offline Salar  Germany
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Default Does the PCM63 accept 16 bit input data only?...

... or is it selectable from 16 up to 20 bit?
As far as i understand the datasheet, the PCM63 does the conversion to 20 bit internally. No word about 20 bit input word lenght from a digital filter.
So does the PCM63 always need 16 bit input data for working properly, or can it be fed with 20 bit?
All the best,
Salar
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Old 19th April 2010, 05:21 PM   #2
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You can feed it with up to 24 bit, but only 20 will be used. Also the precision is guaranteed only up to 17 bit, but that's a different issue.
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Last edited by SoNic_real_one; 19th April 2010 at 05:40 PM.
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Old 19th April 2010, 05:34 PM   #3
Salar is offline Salar  Germany
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Thanks SoNic_real_one
So, it should be better feeding the PCM63 with 16 bit? What is your proposal?
The reason I am asking:
A -60dB 1kHz sine wave sounds distorted. (Wabeform on the scope seems to be o.k.) Not much, one hears slightly a buzzing noise in the background, almost like an open loop, but higher ain frequency and much quieter than the -60dB sine. The PCM634 is fed from a PCM1704 with 20 bit right now, so i was wondering whether I "hear" the missing 4 bits. Those are simply dropped, right?

BTW, I did remove my PCM1704 mod I mentioned in another thread from the DAC.
Too much HF in the outputs, I guess of poor grounding (had to use simple adaptor boards and rewire everything)
But the sine, even though blurry on the scope because og HF-noise, sounded clear...

All the best,
Salar
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Old 19th April 2010, 05:44 PM   #4
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I think it should be working OK with 20 bit at input, even 24 bit (it wil be truncated, last 4 bit will be ignored).
How are you feeding from a PCM1704? That's just a DAC, not a digital OS filter. Maybe DF1704?
Now... I don't know what you hear, it might be someting else - decopling of the analog side from the digital, power supply pins decoupling, OpAmps in the I/V stage oscilating, grond loops picking up HF noise...

Last edited by SoNic_real_one; 19th April 2010 at 05:50 PM.
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Old 19th April 2010, 06:21 PM   #5
Salar is offline Salar  Germany
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Sorry, DF1704. Replaced SM5813 in a Parasound DAC-1500.
Besides the filter, the design is unchanged.
The mod with PCM1704 dacs was done on a second board, its original purpose was to feed the inverted signal of XLR output. (inversion was done digitally between the filter and DACS)
Both boards have independent power supplies.
After the mod was technically not satifsying, I removed the second board and its power supply sections - again, because I had the Parasound already this way before attempting the mod with PCM1704 Dacs (The Parasound runs much cooler with the second board and power supplies removed) but never made the -60dB listening test. But I guess, this is not the reason, might be "natural" for the dac.
As some kind of reference:
16 bit PCM54 4X Oversampling based Nak Player adds a noise in a higher frequency playimg the -60dB tone, a second generation 16 bit-no-oversampling Toshiba XR-Z70 adds more hiss...

On my old scope, (tube, up to 15 mHz) waveforms of all 3 Players/Dacs look the same...
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Old 19th April 2010, 07:43 PM   #6
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Maybe you want too much from a 16 bit format. At -60dB you will have some noises at the -36dB...-40dB - that's VERY easy to hear if you crank up the volume enough.
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