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RE: BPM & Pitch Shift on Repeater

ok, here is how I (now) understand the relationship of tempo change to 
frequency
(pitch) change. First it's important to realize that the percentage of 
frequency
change is equal to the percentage of tempo change, that is if you change
your tempo by +25% then you change your frequency by +25%. And so, the 
question
becomes (and was originally asked) what is the relationship between 
percentage
of frequency change to semitones. 

Each semitone is 2^1/12 (two to the one over twelve) percent change in 
frequency.

In doing the calculation we need to look at the 'tempo/pitch' adjustment
as a 'what percent of the original frequency is the new frequency'

The calculation for going from 'percent of original' to semitones is:

12*log2(%/100)

I've enclosed an Excel spreadsheet with the results that cover the changes
in the range available on the Repeater, as well as putting in an short list
here.

Speed adjustment        % of original           Change in semitones
        -75%                    25%                     -24
         ..                     ..
        -50%                    50%                     -12
         ..                     ..
        0%                      100%                    0
        ..                      ..
        100%                    200%                    +12
        ..                      ..
        150%                    250%                    +15.86...

It's still not clear how the Repeater maps the 128 (0-127) CC messages 
across
the 225 percentages, but once that is known you can combine that info with
this and you will know what you wanted to know.. :)

peace
-cpr

>-- Original Message --
>Date: Thu, 6 Nov 2003 20:28:50 +0000
>Subject: BPM & Pitch Shift on Repeater
>From: Paul Greenstein <paul@ubiq.co.uk>
>To: loopers-Delight@loopers-delight.com
>Reply-To: Loopers-Delight@loopers-delight.com
>
>
>Being a mathematical dunce, I'm having difficulty working out the 
>relationship between midi controller values and tempo/pitch shift.
>
>The manual says:
>
>(using cc 14)  (-75%+150%) adjusts the tempo and pitch as a percentage

>of the current tempo. 76 is zero shift.
>
>I've made this work via trial and error - for example, a value of 25 
>seems to reduce the pitch by -12 , but it would be nice to be able to 
>predict the relative tempo change as well...
>
>Maybe someone out there knows what I'm on about...
>
>
>
>
>Paul
>