$Page Checking for aliasing
$TargetName Checking for aliasing

*What is aliasing*
When generating sound, if any frequencies of its components are higher than roughly half of Live's sample rate, you get new sounds in lower frequencies. This is due to an effect called aliasing.

The /Naive/ track contains an instrument that uses waveform generators without anti-aliasing. To clearly hear the effect of aliasing, it generates a high note. The pitch is slightly modulated by an LFO. 

Naive.png

After increasing the gain in Utility (warning: use low volume), you will hear the moving sounds in the middle of the spectrum that are not supposed to be there. These sounds can also be seen in the spectrum visualisation. The high, slightly moving peaks are the original sound. 

Aliasing.png

The lower, fast moving components are due to aliasing.

The /Anti-aliased/ track contains the same instrument, but with [saw~] instead of [phasor~] and [rect~] instead of a binary comparison. You will notice that here, the aliasing artifacts are almost gone.

Some extra notes:
-> When changing the sample rate setting in Live's preferences, notice that the aliasing sounds change.
-> Have a look at the [saw~] help patch for another demonstration of aliasing.
-> To prevent aliasing when generating more complex waveforms, for example with FM, you can use filters to prevent most high frequencies from ending up causing aliasing.

$Link Learn more about aliasing <https://en.wikipedia.org/wiki/Aliasing#Sampling_sinusoidal_functions>