Coding mono oscillators

stefan · 14 Mar 2005

if you'd just change the output = sin1(cnt); to output = cnt; you'd get an aliasing sawtooth.

another way to do different waveforms is to use phase feedback within the oscillator, for instance like this:

monoin freq; monoout output; float cnt; float feedback; feedback = 0.2;

cnt = cnt + freq; cnt = cnt - ((cnt >= 1.0) & 1.0); output = sin1(cnt + output * feedback);

By adjusting the feedback you can "morph" the waveform between a sine and a saw. If you instead do a feedback with the phase "squared" you'll get a pulse waveform, like this:

output = sin1(cnt + output * output * feedback);

Too high feedback rates will introduce an instability that is undesired, so keep away from doing that.

You can also create pulsewaveforms by mixing sawtooths (invert one of them and you'll get a pulse with variable pulse width by moving the phase of one of the oscillators)

galaa · 15 Mar 2005

🙂 🙂 🙂 🙂 where have you been all my life!!!!

Fantastic. Thanks a lot for your help.

Now all I've got to do is pick the code apart and try and figure out what its doing. Can you recommend any textbooks/websites/etc where a DSP newbie can learn all about this kind of thing

stefan · 15 Mar 2005

Recently this huge gem was posted on kvr http://math.uga.edu/~djb/html/music.pdf

it's an awesome resource and getting updated when needed etc. great book. for free, whic is totally "wtf".

galaa · 15 Mar 2005

Thanks I've downloaded it. It's massive!!! Gonna take a while to read through that!!!! 😀

galaa · 15 Mar 2005

stefancrs wrote: You can also create pulsewaveforms by mixing sawtooths (invert one of them and you'll get a pulse with variable pulse width by moving the phase of one of the oscillators)

How would I create a piece of code that enabled me to vary the phase of one of the sawtooths. I am using the following code you posted:

monoin freq; monoout output; float cnt; float feedback; feedback = 0.2;

cnt = cnt + freq; cnt = cnt - ((cnt >= 1.0) & 1.0); output = sin1(cnt + output * feedback);

I am just guessing, but would I define the 'cnt' variable as having a non-zero starting value.

stefan · 15 Mar 2005

galaa wrote: stefancrs wrote: You can also create pulsewaveforms by mixing sawtooths (invert one of them and you'll get a pulse with variable pulse width by moving the phase of one of the oscillators)

How would I create a piece of code that enabled me to vary the phase of one of the sawtooths. I am using the following code you posted:

monoin freq; monoout output; float cnt; float feedback; feedback = 0.2;

cnt = cnt + freq; cnt = cnt - ((cnt >= 1.0) & 1.0); output = sin1(cnt + output * feedback);

I am just guessing, but would I define the 'cnt' variable as having a non-zero starting value.

just do it like this:

monoin freq; monoin phase; monoout output; float cnt; float feedback; feedback = 0.2;

cnt = cnt + freq; cnt = cnt - ((cnt >= 1.0) & 1.0); output = sin1(cnt + phase + output * feedback);

you can also use the phase input as a fm input.

galaa · 15 Mar 2005

Ah of course much simpler and you can have control over the phase value. Thanks you're a great help