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Old 17th February 2009, 08:15 AM   #1
poynton is offline poynton  United Kingdom
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Default SPDIF - Is it always the same?

Hi.

While reading the thread on the Philips CD723, I came across this..

Quote:
The other problem is the digital filter in the SAA7378 is mediocre at best. The internal resolution is not sufficient at all, stop-band attenuation is very poor, and a -0.5dB downscaling is applied on all input signals to prevent overflows. The chip doesn't even dither before this downscaling. Thus, you will never get accurate samples from the CD out the I2S of the chip!
It made me wonder, if data is "tampered " with in some cd players, is the SPDIF output always the same ?

Andy
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Old 17th February 2009, 08:46 AM   #2
Giaime is offline Giaime  Italy
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No, the SPDIF is also corrupted: read here
http://peufeu.free.fr/audio/extremist_dac/bit_accuracy/
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Old 17th February 2009, 09:01 AM   #3
phofman is offline phofman  Czech Republic
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The digital filter is the first stage of DA conversion. It would make sense to tap the SPDIF signal BEFORE the filter, otherwise the SPDIF stream would be the upsampled one, e.g. 352.8kHz
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Old 17th February 2009, 10:48 AM   #4
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Quote:
Originally posted by Giaime
No, the SPDIF is also corrupted: read here
http://peufeu.free.fr/audio/extremist_dac/bit_accuracy/

I was not refereing to te CD723 in particular but was asking the question in general.

So I guess one answer would be it depends on the chipset.

Andy
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Old 17th February 2009, 10:55 AM   #5
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Quote:
Originally posted by phofman
The digital filter is the first stage of DA conversion. It would make sense to tap the SPDIF signal BEFORE the filter, otherwise the SPDIF stream would be the upsampled one, e.g. 352.8kHz

This is what happens in the SAA7220.

I assume therefore that, in this case, the SPDIF is "uncorrupted".

Andy
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Old 17th February 2009, 11:04 AM   #6
phofman is offline phofman  Czech Republic
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I would dare saying the digital volume control in CD723 is more of an exception than a rule. I tested several CD players (some old Philipses and Denons) and they were bit-perfect. I cannot talk about new machines (e.g. HK CD970) with DSP etc.
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Old 6th March 2009, 01:39 PM   #7
poynton is offline poynton  United Kingdom
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I was interested in modding a player with the SAA7341 DAC.

In the specs, it states that the signal is cliped toprevent overflow.

So I guess the output is not bit perfect.


( The SPDIF is taken off before any upsampling is done .)


Andy
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Old 7th March 2009, 12:03 AM   #8
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I think the clipping block would be embedded into the noise-shaper itself, in which case an S/PDIF stream tapped off before the oversampler couldn't be corrupted by it.
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