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.