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Tim I
2006-07-28, 08:08
search the forum but didn't find an answer.
How does the SB3 output 24bit from a 16bit input?
Does it just add 8 zeros or another algorithm. Also is i possible to change it to output 16bit so I could use another processor to increase bit depth?
many thanks

seanadams
2006-07-28, 12:28
search the forum but didn't find an answer.
How does the SB3 output 24bit from a 16bit input?
Does it just add 8 zeros or another algorithm. Also is i possible to change it to output 16bit so I could use another processor to increase bit depth?
many thanks

It's not really "adding zeroes" but just putting a 16-bit number in the 24-bit slot that s/pdif provides.

At less than full volume, the additional bits are used to _maintain_ the resolution of the original signal, but you can't effectively _increase_ it. If you want to ensure 16-bit passthrough with the additional bits being zeroes, choose "fixed digital volume" in player settings.

Again, there is no way to "increase bit depth" - you can't recover information that isn't there. Also, whatever processor you want to use should not have a problem with a 24-bit input. If it doesn't know how to deal with 24-bit then it will only look at 16 of them.

John Stimson
2006-11-01, 15:16
This seems to relate to a question I have:

Is it possible to enable replaygain for the Squeezebox2 such that a 16 bit source file is adjusted for gain and output at 24 bit resolution on the SPDIF output?

How would I achieve that? Is it the default behavior when the automatic volume adjustment feature is enabled?

I have a 24-bit cabaple external DAC and I would like to make use of the replaygain feature without truncating to 16 bits. I think I tried turning on the automatic volume adjustment once upon a time, and got 16 bit output to the external DAC.

John Stimson
2006-11-01, 23:01
Maybe my question was too open-ended. So:

When Volume Adjustment/ReplayGain is enabled, what bit depth is the signal coming out of the SPDIF output of the Squeezebox2?

radish
2006-11-02, 09:17
As far as I know it's always 24-bit. My understanding is that RG is applied using the same algorithm as the regular digital volume control.

John Stimson
2006-11-02, 14:31
That would make sense for the internal data going to the internal DAC since the designers know it will take 24-bit input.

I would be a bit surprised if the SPDIF output defaulted to 24-bit since some external DACs only take 16-bit input. I suppose you could still use those DACs by disabling replaygain and digital volume control in the Squeezebox.

I'd like to know for sure whether that's how it works. I suppose I could hook up the SPDIF output to my computer's SPDIF input and see for myself, eh?

John Stimson
2006-11-06, 17:28
According to Slim tech support, the SPDIF output is converted to 16 bit. I have opened an enhancement request (http://bugs.slimdevices.com/show_bug.cgi?id=4479) to ask for the option of leaving it at 24-bit.

ezkcdude
2006-11-06, 17:49
The output is 16 bit at full volume, but 24-bit otherwise.

radish
2006-11-06, 19:32
I would be a bit surprised if the SPDIF output defaulted to 24-bit since some external DACs only take 16-bit input. I suppose you could still use those DACs by disabling replaygain and digital volume control in the Squeezebox.

16-bit only dacs just throw away the least significant byte, so they still work just fine.

John Stimson
2006-11-07, 13:44
The output is 16 bit at full volume, but 24-bit otherwise.That's at odds with what I was told by Slim tech support. Do you know something they don't?

I would love to be able to check for myself, but unfortunately I don't have any windows software that will tell me what is coming in on the sound card's SPDIF input.

By the way, that's your 666th post, so right away I know I shouldn't trust it ;)

radish
2006-11-07, 17:27
According to Sean's posts on the audiophile forum, the output from an SB is always 24 bit. Assuming (a) the source material is 16-bit lossless and (b) the digital volume is at max, then the output will be the original 16-bits padded with a 0 byte. In any other case (including mp3 source material, non-full volume, RG, etc) the full 24-bits of accuracy will be used. A 16-bit DAC will just ignore the lower byte.

Wikipedia (http://en.wikipedia.org/wiki/Spdif#Protocol_specifications) explains the wire format a little more, it says that SPDIF is designed for 20-bit, can be made to transmit 24-bit, but it's always up to the DAC to take as much resolution as it wants.

mswlogo
2007-04-15, 07:58
This is not true.

16bit in you get 16bit out (at SPDIF anyway).

If this were not true a ripped 16/44.1 DTS CD would no pass through the squeezebox to your DTS receiver/preamp.

I assume 24/44.1 it would also come out as 24/44.1 but I have not tested that.

Every data rate / word size I have used so far has passed through (clock rate and word size). Except 24/96 is downsampled to 24/48.