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From: gibson@unc.UUCP (Bill Gibson)
Newsgroups: net.music.synth
Subject: Digital delays
Message-ID: <1176@unc.unc.UUCP>
Date: Thu, 27-Mar-86 22:58:41 EST
Article-I.D.: unc.1176
Posted: Thu Mar 27 22:58:41 1986
Date-Received: Sat, 29-Mar-86 16:17:25 EST
Reply-To: gibson@unc.UUCP (Bill Gibson)
Organization: CS Dept, U. of N. Carolina, Chapel Hill
Lines: 31
Keywords: analog/digital shift register

Expires:
References:
Sender:

>> Of course, a long hardware shift register should be easier to control
>> than the RAM, but I didn't realize that such a register exists (unless
>> you're referring to an analog bucket-brigade delay line). 

>Yes... there is a 1024-bit shift register, the SAD-1024, made specifically
>for this purpose.  

Aha! This tells me what we have been talking about. I remember the SAD-1024
being a *S*tereo *A*nalog *D*elay, a bucket-brigade delay in which charge
sloshes along in 2 lines of 512 buckets each. I think that the device was
originally designed to be used with analog inputs and outputs, but I guess
you could shift bits through it instead. If this device is used as a digital
shift register, is the noise introduced by the charge-transfer between buckets
small enough so that bits reliably pass through?

I think the SAD-1024s I got were about $11 each. If you consider the device
to be a 1024 bit shift register, this means that they have a cost/bit of 
about $.01/bit.
The following pricing is taken from net.micro.atari (referring to a 
520ST upgrade):
>    16 256K * 1 RAM chips, 150 ns access time type, e. g. NEC 41256C-15
>    (available at Fry's Electronics, Sunnyvale, CA for $2.77 ea.)
This is about $.01/Kbit, or about a thousand times cheaper than the SAD-1024.
Although the SAD-1024 might be easier to control, the difference in price
could buy a lot of control hardware for the RAM!

If I were interested in long delay times and high-frequency sampling, I'd
probably design with the RAM instead of the SAD-1024.

Bill Gibson
gibson@unc                   ...[akgua,decvax,philabs]!mcnc!unc!gibson