Re: [LAD] Half-OT: Fader mapping - was - Ardour MIDI tracer

On Thu, 21 Aug 2014, John Rigg wrote:

> On Thu, Aug 21, 2014 at 09:01:03AM -0700, Len Ovens wrote:
>> On Thu, 21 Aug 2014, John Rigg wrote:
>>> The '70s Neve mentioned earlier would likely have used Penny & Giles faders
>>> with a roughly logarithmic taper (no VCAs). Since this type of fader is made
>>
>> Ok, I have to ask this somewhere, it may as well be here :) Which
>> log?
>
> The P+G faders (generally regarded as the best) are close to log10
> characteristic, ie. -20dB at about half travel. There's a PDF data sheet
> here:
>
> http://www.pennyandgiles.com/Products/Audio-Faders-Video-Controllers/Linear-Manual-Fader-PGF8000.aspx
>
> The Panel Graduations/Slots diagrams on page 3 show the taper characteristic.

Interesting. Out of that I get what looks like two log areas and a third
area that biases towards linear:

   0 -> -10 = 23.12
-10 -> -20 = 25.2
-20 -> -30 = 12.8
-30 -> -40 = 11.8
-40 -> -50 = 12
-50 -> -60 = 5.5
-60 -> -70 = 3.1
-70 -> inf = 6.1

So 0 to -20db is log (about 12mm / 5db)
-20 to - 50db is log (about 12mm / 10db)
-50 to inf is what looks like a straight line from -50 to ground/inf

So while the first two sections are log, they are not the same scale of
log. It is like the top half of the fader is from a fader that would be
from 0 to -40db. The next half is from a 50mm fader that is 0 to -40db but
the last 10 or 12db are linearish from that point to the bottom. The fact
that there are some places that look smaller than they should be (-30 to
-40... or maybe -40 to -50 is too big?) is to allow smooth transitions
from one part of the taper to the next. Fantastic engineering making the
most of the length for usability. I expect this layout came from the days
when a fader was made out of individual pads and a big switch. The pads
were 2db apart or so. The one I saw was rotary.

--
Len Ovens
www.ovenwerks.net
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