All my Cabbage projects have Aliasing problems!

[Kosmo3000]

Hi,

Exists one way to eliminate the aliasing problems that are presents on all my projects with Cabbage/Csound?
For example,
when I create a simple FM project with 2 sine oscillators, and increase the INDEX, there is too much presence of aliasing in the audio output signal: if I change the waveform with another more complex, the presence of aliasing rise!

If I use one band limited oscillator, when is modulated with another, aliasing disturbances are presents in the audio output signal.

Or, when one table generate the wave profile for one oscillator, the aliasing appears in the upper notes…

There are many other examples showing these problems, which is why I open this request.
The only wrong solution I use is to put an LPF on SR / 2 on the main audio output … but it doesn’t work properly …

Please help me… thanks

[rorywalsh]

@Kosmo3000

For example,
when I create a simple FM project with 2 sine oscillators, and increase the INDEX, there is too much presence of aliasing in the audio output signal:

Your output spectrum will be composed of the sum and differences of the modulators and the carrier. So if your index is high then there is a very good chance of aliasing.

@Kosmo3000

if I change the waveform with another more complex, the presence of aliasing rise!

This makes sense because you are increasing the number of sidebands, therefore increasing the likelihood of aliasing.

@Kosmo3000

If I use one band limited oscillator, when is modulated with another, aliasing disturbances are presents in the audio output signal.

Same thing here. If you are using a bandlimited complex waves there is a very high chance of aliasing.

@Kosmo3000

There are many other examples showing these problems, which is why I open this request.
The only wrong solution I use is to put an LPF on SR / 2 on the main audio output … but it doesn’t work properly …

Applying a low pass filter after the fact won’t help at all, as you’ve already noticed.

I’m not an FM expert, but you could try dynamically reducing your index as you play higher notes. Of course it will also affect the timbre at higher frequencies. I think most commercial FM synths use oversampling, whereby they employ a much high SR to avoid fold-over.

Perhaps @iainmccurdy has some advise he can share about this. He has written quite a few FM examples in his day!