Sound quality issues (was: RE: echoplex or jamman?

[Chuck Zwicky <chuck.zwicky@wavefront.com>]

At 09:07 AM 10/30/98 -0500, you wrote:
>You're right about the tambourine dynamic range, Kim.  What's more,
>tamborine is RICH in frequencies above 20 Khz, all the way to the 50 KHz
>range.  This will get past the anti-aliasing filters, rendering them less
>effective. 
>This is one of those special cases where higher digital sampling frequency
>would be of great advantage.

I disagree. The Jamman does not have these problems, and it has a slightly
lower sampling rate. The problem in the EDP are the analog electronics and
the poor layout. 

On the Analog side there is NO anti-alias filter on the input before the
converter. This, in addition to the pre-emphasis, which starts boosting the
high frequencies around 200HZ  at a rate of 6dB per octave makes the input
very sensitive to aliasing.

I experimented with modifying the pre-emphasis/de-emphasis filter, but
found the noise floor so obnoxious that I left it stock. The noise I am
describing is the result of poor layout and grounding on the PC board. Lots
of metallic clocking artifacts.

The Jamman has a very nice LRC filter on both the input and the output. I
have never heard it get nasty, even when overdriven.

Please remember that I don't work for Oberheim or Lexicon. 
It is my hope that Oberheim will look into the possibility of redesigning
the EDP. The AD1848 converter is quite horrible by todays standards. 

The EDP software is absolutely brilliant. The EDP audio design is
stombox-esque crap.

I'm sorry that all this has made Kim so defensive. I hope that he will sit
down with an open mind and listen to the Jamman and the EDP side by side. 

"Defend your weaknesses and they're yours to keep forever."


-Chuck Zwicky