Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!gatech!gitpyr!byron From: byron@pyr.gatech.EDU (Byron A Jeff) Newsgroups: comp.dsp Subject: More digital mixer stuff Message-ID: <9238@pyr.gatech.EDU> Date: 28 Sep 89 23:40:30 GMT Reply-To: byron@pyr.gatech.edu.gatech.edu (Byron A Jeff) Organization: Georgia Institute of Technology Lines: 95 Todd: My mail to you bounced. So I'm posting my reponse. > >~----------- --------- --------- -------- -------- -------- -------- >~|8 |--|Analog |--|Filters|--| |---| | | | | | >~|Audio |--|Multi- | | and | | ADC | | DSP |--| DAC |--|Filter| >~|channels |--|plexors|--| S/H |--| |---| | | | | | >~----------- --------- --------- -------- -------- -------- -------- > ^^ ^^^ > Eight lines here. There should be two lines since it > is a dual ADC. I don't have all the specs yet. I hadn't had a chance to read the article. The two observations you made above are correct. > >Sounds like it might be feasible. Does it have serial or parallel output? > >Serial > 44.1 kHz * 4 channels * 16 bits/channel = 2.822 MHz > >I think the 56000 can handle this. Only half of what you need, though. >You might be able to do it with the TM$32030, as it has two serial inputs. Even if it were serial I'd probably just shift it into shift registers and read in the parallel outputs when all of the bits of a complete sample has been shifted in. > >Parallel > Either 56000 or 32020 can handle this, if you can figure >out a way to merge the data streams. > >~If samples can be obtained for ~$50 then a box for between $200 to $300 >~could be realized. If the DSP is fast enough then another ADC could >~easily be added for a grand total of 16 channels. > >Your biggest problem is that the samples are not arriving at the same >time. Actually, I guess you could use an interrupt routine to store all >the samples, then have the DSP act on them when all have arrived. That's exactly what I was thinking. Something along these lines: Sample 1 Sample 2 Sample 3 Sample 4 Output of mix of the 4 above samples. --------Time Axis---------> > >Remember that since you are using an analog MUX, the samples can't all >be done at EXACTLY the same time, so there will be a slight delay between >all of the channels. I'm brand new in this domain. I have no clue what the effect of the delay between channels will be. Can you give me an idea? > >Also, if it is serial, you'll have to use TWO 56000s and have them >talk to each other (not really that hard). Could do some killer >filtering, though. Again with some parallel shift registers that problem disappears. Right off the top of my head I think you can clock a 74LS164 at 30 Mhz so the speed is not a problem. Another reponse I saw indicates that a 56001 wouldn't be able to handle mixing 8 channels much less doing any kind of EQ, reverb, etc. He suggested a DSP for each channel. I was of course in pain as this is strictly hobby material for me. Can you give me an idea of how much processing power a 56001 has? An estimate of how much of the above (getting data, mixing, providing effects) a single 56001 can do would be quite helpful. 2 I'd be willing to deal with but my whole concept is to reduce the parts count to a fairly small board. > >There might be some chips from AT&T that are cheap and have two >synchronous serial inputs. The TI chip I mentioned is expensive. > Also thanks for all of the articles you've been posting and the server (which I haven't had a chance to use yet). It's all been quite informative. Keep it up. Thanks also for the reponse. I'm saving all of the them and will summarize the results in a little while. BAJ -- Another random extraction from the mental bit stream of... Byron A. Jeff Georgia Tech, Atlanta GA 30332 Internet: byron@pyr.gatech.edu uucp: ...!gatech!pyr!byron