Re: sample clock playback tricks

[Kim Flint <kflint@chromatic.com>]

At 03:08 PM 2/5/98 EST, MIvanBerk@aol.com wrote:
>In a message dated 98-02-05 14:53:28 EST, Kim wrote:
>
><< interesting problem, new technology comes along, making huge 
>improvements
> in some ways and obsoleting the old stuff. But there's usually some
> characteristic of the old stuff that becomes very difficult in the new
> technology. And then you need a few more generations of new technology
> before you are able to do the old idea again. In this case, you used to 
>be
> able to easily change the sample clock on A/D and D/A convertors, and 
>they
> would be happy and nothing else in a simple delay system would get 
>screwed
> up. Nowadays, the convertors give better audio but don't let you do that
> sample clock trick anymore, and other things in the system that need
> accurate timing (like midi) get screwed up. So for the echoplex and 
>jamman,
> this sort of thing is impossible. So now you need to add a fair amount of
> dsp processing and more sophisticated real-time os techniques to be able 
>to
> do what once just required a very cheap part. such is progress....
> 
> kim >>
>
>Any idea how the Boomerang folks got around this problem, at least 
>insofar as
>their unit offers half speed/half sample rate playback?  Boomerang folks?

I don't know how Boomerang does it, but half speed is usually quite easy
with the current crop of A/D convertors. You usually have a few fixed 
sample
rates available that can be selected by the processor, these tend to match
sample rates used in various common devices: CD's, DAT, sound cards, etc. 
So
you just switch it on the fly. Variable sample rates, on the other hand, 
are
not so easy. Boomerang also doesn't have to deal with sync, so the question
of "what the hell do we do with the midi clock when the user is goin' mad 
on
the delay time knob?" is not an issue for them.

kim
________________________________________________________
Kim Flint                      408-752-9284
Mpact System Engineering       kflint@chromatic.com
Chromatic Research             http://www.chromatic.com