[sdiy] Modulating the Eprom adress!

[Magnus Danielson]

From: karl dalen <dalenkarl at yahoo.se>
Subject: [sdiy] Modulating the Eprom adress!
Date: Sat, 12 Aug 2006 22:30:15 +0200 (CEST)
Message-ID: <20060812203015.46169.qmail at web27603.mail.ukl.yahoo.com>

> Lets say you have a saw osc reading out the info from a eprom 
> (digitally stored wave info) then let another sine osc read out 
> a smaller portion of the same address area (basically offsetting
> the saw wave in amplitude, still maintaining the same amunt of range)
> at audio rate, what would you call this type of modulation?
> 
> FM, phase distortion, audiorate waveshaping?
> 
> The saw frequency is not modulated by the sine, nor is the sine modulated by
> anything. 

Phase modulation.

Your sawtooth wave is infact acting as a steping through a linear set of phases
from 0 to 360 degrees. When you add a signal to that prior to your waveform
function (stored in the EPROM) you will modulate the phase of the resulting
waveform. If the wavetable is one sine cycle, it is very easy to understand
since the sine will drift back and forward in its phase.

PM made the DX7 tick.

Cheers,
Magnus