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From: rsk@pucc-j (Wombat)
Newsgroups: net.music.synth
Subject: Re: Digital delays
Message-ID: <974@pucc-j>
Date: Thu, 27-Mar-86 12:04:56 EST
Article-I.D.: pucc-j.974
Posted: Thu Mar 27 12:04:56 1986
Date-Received: Sat, 29-Mar-86 16:00:49 EST
References: <1848@decwrl.DEC.COM>
Reply-To: rsk@pucc-j.UUCP (Wombat)
Organization: Purdue University
Lines: 37

In article <1848@decwrl.DEC.COM> janzen@pldvax.DEC (Tom J. LMO2-1/E5 279-5421) writes:
>A "bucket-brigade" is an analogue circuit which passes stored voltages...

>I also meant to say that this M.O. is dead wrong.  Modern delays use
>RAMs, and the data does not snake its way through the memory, although it
>does through CCDs, which are not digital.

>CCDs are limited to about 1024 samples on a chip, and are prone to noise
>of various types, so chaining chips to accumulate delay. is not desirable.

Oh, get stuffed!  I used simplistic terminology *correctly*, in
attempting to explain the fundamentals of digital delays.  I am
perfectly aware of the use of RAM-based implementations in some modern
units; however, I felt that it wasn't necessary to explain the complex
model when the simple one would do.  However, it would appear that you
are unaware of the existence of digital CCD's, which are frequently
used in applications where random access is not required -- and that's
a lot of applications.

CCD memories [Such as the TI 3064] are frequently referred to as
"bucket-brigade" devices, since the digital signal propagates through
them in much the same way that an analog signal propagates through an
analog delay line.  There's no need for fancy addressing schemes and
fast RAM if all you want to do is delay a signal for a fixed period of
time or similar simple tasks.  Your nitpicking, followed by a
substantially similar explanation, sheds no additonal light on the subject.

>I am designing a harmonizer.

Fine.  Let's compare credentials.  The digital delay I designed is in
use daily in hundreds of studios and radio stations around the country,
was one of the first (if not the first) to use a variable loopback in
order to shift time without changing the pitch, and earned a patent for
the manufacturer, as it was the first to use a digital delay line based
on CCD's, along with companding ADC/DAC circuitry.
-- 
Rich Kulawiec  pucc-j!rsk or rsk@asc.purdue.edu