Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uakari.primate.wisc.edu!ginosko!uunet!mcsun!sunic!draken!d88-jwa
From: d88-jwa@nada.kth.se (Jon W{tte)
Newsgroups: comp.dsp
Subject: Re: More digital mixer stuff
Message-ID: <1845@draken.nada.kth.se>
Date: 3 Oct 89 01:43:37 GMT
References: <9238@pyr.gatech.EDU> <7905@microsoft.UUCP> <9247@pyr.gatech.EDU>
Reply-To: d88-jwa@nada.kth.se (Jon W{tte)
Organization: Royal Institute of Technology, Stockholm, Sweden
Lines: 33

In article <9247@pyr.gatech.EDU> byron@pyr.UUCP (Byron A Jeff) writes:
>The only question is what's the sample rate of the mixed signal? It
>would seem to be 8x the original sample rate yes? So for 8 48Khz channels
>I'd need a 384 Khz DAC. Ouch! 

No, not really. You apply a digital filter on the signal, and then use
each eigth sample. Yes, it'll work ! Someone said that you should apply
this BEFORE you fed the signal to the DSP, but then you would have no
channel separation (the channel separatio is in the time domain if you
interleave the samples, and the filter truly messes this up) and all the
channels would come out mixed equally.

>-In any event, those manufacturers are merely trying to sell you two DACs
>-instead of one, when a single converter and a few sample and hold stages
>-would realign the reconstructed signals.  One S/H could be used to

But using one DAC also introduces some distortion in switching between
channels !

>>transitions take longer than 1 to 0 transistions.  Then, for a digital
>>sample changing from $8000 to $7FFF, you would first get $0000 on the
>>DAC output before all the other 15 bits changed to $7FFF.  Ugly and BIG
>>spike!  Analog sample and hold allows the outputs to be disconnented

Heard about (a) a latch and (b) an analog filter after the DAC ?
Wouldn't this take care of such things ? ARE there S/H stages after
the DAC in good CDs ? I don't think so, but please correct me, if you
know for * SURE *.

Says,
		h+@nada.kth.se
-- 
Mooo.