Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!gatech!gitpyr!byron
From: byron@pyr.gatech.EDU (Byron A Jeff)
Newsgroups: comp.dsp
Subject: Re: More digital mixer stuff
Message-ID: <9241@pyr.gatech.EDU>
Date: 29 Sep 89 22:37:37 GMT
References: <9238@pyr.gatech.EDU> <1989Sep29.102204.8798@ivucsb.sba.ca.us>
Reply-To: byron@pyr.UUCP (Byron A Jeff)
Organization: Georgia Institute of Technology
Lines: 66

-~[Byron]
-[Todd]
-~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.
-
-What I was refering to was the *built-in* serial shift registers in
-the DSP chips.  That way, you wouldn't need the glue logic.

But as you stated it's only one channel unfortunately. If the design
decision comes down to a choice of TI, 2 56001's, or external shift
registers with a single 56001 I'll probably go with the external glue.
How can I lose at $0.59 a pop? ;-)

However if I turn out to need 2 56001's do handle the processing then
I'll use the internal shift registers. I'm working on a shared memory
controller between two 68008's and a 68010 right now for my kick-ass
MIDI box. I might be able to apply it here somehow.

-
-~>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?
-
-Ch 1 - delay - Ch 2 - delay - Ch 3 - delay - Ch 4
-
-The delay will be the length of time it takes to switch from one
-channel to the next via the MUX and then sample with the sample/hold.
-Probably not very signifigant, but those who spend $1000 on interconnects
-for their stereo systems would probably complain.  Of course, they wouldn't
-be listening to digital, anyway, would they? :-)

I'm hoping it's not significant. And I can't hear the phase shift when I
reverse polarities of the Monsta Leads to my $4000 Polk Audio speakers
either ;-)

-
-~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 know that one chip can *at least* emulate a 2 channel 10 band 12 dB
-equalizer from a Motorola app note.  I wouldn't think that reverb would be
-that tough to do.

Good to hear. I could live with effects on the mixed signal even though
having individual effects on each channel would be cool. Not worth
eight 56001's cool though.
-
--- 
-
-Todd Day  |  todd@ivucsb.sba.ca.us  |  ivucsb!todd@anise.acc.com
-"Ya know, some day these scientists are going to invent something
-	that can outsmart a rabbit" -- Bugs Bunny

After reading your series on building a beast and your discussion so far
on this mixer I feel very optimistic about the idea. Thanks.

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