zipper noise was: digital control

[Grant Richter]

You use a DAC with a very large number of bits,
taking the incoming 0-127 controller levels you
predict a series of higher resolution line segments
based on the spacing of the controller messages.

That is to say the microprocessor is continuously
trying to predict a line segment that will arrive at
the next controller point in time with the message.

----------
> From: harrybissell at prodigy.net
> To: DCMagnuson at aol.com
> Cc: synth-diy at mailhost.bpa.nl
> Subject: Re: zipper noise was: digital control
> Date: Wednesday, January 12, 2000 9:47 AM
> 
> Yes... you can put a "glide circuit" or lowpass filter on the DAC output.
The trouble is... what rate to filter at. If you do a very slow (manual)
filter sweep... you need a very long time constant. If you "whip" the dial
quickly... the long sweep will fight you.
> 
> You could detect how fast the dial is moving and filter slow or fast
(either digital of analog) or have so many bits and clock so fast that
no-one can hear it.
> 
> The Studio Electronics AT1 (???) the "tone chamelion" model with the
single "Alpha Dial" is the only hybrid synth I have ever heard that does
not have zipper noise... Even at high resonance settings it is dead smooth.
I'd consider buying it just for that reason. I wonder how they did it ???
> :^) Harry
> 
> 
>  ---- On Jan 11 DCMagnuson at aol.com wrote: 
> > In a message dated 1/11/00 9:36:41 PM Eastern Standard Time, 
> > harrybissell at prodigy.net writes:
> > 
> > > The other problem is "zipper" or step noise... when you move a value 
> > through 
> > > a
> > >  linear range (especially an oscillator or filter sweep) you hear
jumps in 
> > > the
> > >  audio (like a zipper...)
> > >  Really good programming chops can cover most of this up...
> > >  
> > 
> > Here's a question... I haven't ever built a glide circuit, so I haven't
been 
> > able to try this yet, but if you put a glide circuit on your DAC
output, 
> > would it cover up the zipper noise?  I was figuring this would work
well in 
> > non-critical situations (like a filter sweep)
> > 
> > Dave Magnuson
> > Independent Music Site
> > http://www.indiemusicsite.com
> 
>