PWM on complex audio signals

[Don Tillman]

   Date: Tue, 02 Jan 2001 22:20:39 +0100
   From: Magnus Danielson <cfmd at swipnet.se>

   There are many reasons not to like Baxendall's tone controls, but I
   would please ask you to elaborate some on this topic. I'd also love to
   hear some comments on what you would use instead and why.

It's not so much Baxendall tone controls per se, it's hifi style tone
controls in general.  Hifi style tone controls are designed for subtle
adjustment of the balance of the highs and lows with respect to the
mids with minimal interaction.  Which is what you want for hifi.

But on a guitar, or any electronic musical instrument for that matter,
you want to make dramatic changes to the response.  The tone controls
on a guitar amp (Leo Fender's originals or any of the variations)
throw radical hills and slopes into the response curve.

Another issue is that a guitar has a limited frequency range; there
are no subharmonics so there's nothing below 82 Hz (low E) and pickups
don't put out anything over 4 to 6 kHz, depending on the pickup
design.  With hifi tone controls on a guitar, when you turn up the
bass or treble control the greatest amount of boost occurs at the
extreme frequencies (below 82 Hz, above 6 kHz) where the instrument
isn't putting out any signal.  So the treble control ends up operating
as a hiss level control and the bass control ends up as a hum level
control.  Not good.

The right thing is a tone control that makes the greatest changes to
the instruments' midband frequencies.

(There's also the "existance proof"; it's hard to name a respected
guitar amp with Baxendall tone controls.)

(All my opinion, of course.)

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com