-100dB 16bit data through ASRC 24/96 dac -pics

A 8 · 29th April 2004, 05:11 PM

I managed to get my hands on an oscilloscope and took a few pictures.

The measurements are done at the power amp output, the dac is a CS8420/DF1704/Balanced PCM1704K/ with passive IV conversion.

The spdif data originates from an old Pioneer PDS-802 fitted with another CS8420 set for 16bit in and 24/48 out.
The disc generating the -100dB and -90dB dithered data is an old test disc from HiFi News & Record Review produced by Martin Colloms.

I am not sure what I am seeing here, looking at the -100dB signal, are the PCM1704 switching the least (7) significant bits on and off or what....?

Any thoughts or insights are welcome!

/Michael

A 8 · 29th April 2004, 05:13 PM

That was the 16/44 -100dB data...

This is -90dB 16/44 data

BTW..there is no low pass filtering and the poweramp runs up to 500Khz

tiroth · 29th April 2004, 05:41 PM

I don't know how you are inferring that from the pic (when you say -100dB do you simply mean digital silence?), but yes, the LSBs will be affected due to dither. The 16-bit signal occupies the top 16 MSBs so when dither is applied it affects the remaining LSBs for 24-bit output.

A 8 · 29th April 2004, 05:58 PM

-100dB refers to the -100dB test track on the disc, digital silence does not show the pattern I posted, it shows a flatline without the "spikes"

tiroth · 29th April 2004, 06:01 PM

Ok, that does make sense. It is probably just a few bits turned on periodically to make the DAC generate some output.

Bernhard · 29th April 2004, 06:24 PM

Hi,

-100dB is very very low.

Philips used -60dB and I suggest a spectrum analyzer because the scope tells nothing.

Bernhard

A 8 · 29th April 2004, 06:25 PM

I was under the impression that the asrc would interpolate, creating intermediate values and not just re-sample the same value until the next one comes along?

A 8 · 29th April 2004, 06:32 PM

But I can not get to one, anyway I was trying to understand the bit transisions.

-60dB actually looked pretty nice though, smooth and "kind off" clean.

Not 100% sure but I think this was -80dB.

tiroth · 29th April 2004, 06:34 PM

It does, and I've watched AD1896 do it. Otherwise only 1 bit would change.

To see this easily, connect channel A to LRCK, channel B to SDATA (DOUT) and trigger on channel A. You can see each bit value this way, and the LSBs are clearly active.

If you have a third channel to display BCK it makes it even easier to see the transition points.

Bernhard · 29th April 2004, 06:36 PM

Quote:

Originally posted by A 8
-60dB actually looked pretty nice, smooth and "kind off" clean.

Not 100% sure but I think this was -80dB.

And you won't recognize small distortions from looking at the waveform.

If it starts looking ugly, it already sounds very ugly.

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29th April 2004, 05:41 PM	#3
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	I don't know how you are inferring that from the pic (when you say -100dB do you simply mean digital silence?), but yes, the LSBs will be affected due to dither. The 16-bit signal occupies the top 16 MSBs so when dither is applied it affects the remaining LSBs for 24-bit output.

29th April 2004, 05:58 PM	#4
A 8 diyAudio Member Join Date: Mar 2003 Location: Gothenburg	-100dB refers to the -100dB test track on the disc, digital silence does not show the pattern I posted, it shows a flatline without the "spikes"

29th April 2004, 06:01 PM	#5
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Ok, that does make sense. It is probably just a few bits turned on periodically to make the DAC generate some output.

29th April 2004, 06:24 PM	#6
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	Hi, -100dB is very very low. Philips used -60dB and I suggest a spectrum analyzer because the scope tells nothing. Bernhard

29th April 2004, 06:25 PM	#7
A 8 diyAudio Member Join Date: Mar 2003 Location: Gothenburg	I was under the impression that the asrc would interpolate, creating intermediate values and not just re-sample the same value until the next one comes along?

29th April 2004, 06:34 PM	#9
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	It does, and I've watched AD1896 do it. Otherwise only 1 bit would change. To see this easily, connect channel A to LRCK, channel B to SDATA (DOUT) and trigger on channel A. You can see each bit value this way, and the LSBs are clearly active. If you have a third channel to display BCK it makes it even easier to see the transition points.

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