myths and facts about aliasing

A recent trend in the audio producer scene seems to be to judge an audio effect plug-in just by analyzing the harmonic spectrum, which is usually done by throwing a static sine-wave right into the plug-in and then look at the output with a FFT spectrum analyzer afterwards. In this article I’m going to talk about what this method is capable of and where its limitations and problems lie and that aliasing gets confused with a lot of other phenomenons quite often. I’m also clearly showing that this method alone is not sufficient enough to judge an audio plug-in’s quality in a blackbox situation.

a spectrum plot showing noise, harmonic distortion and aliasing

a harmonic spectrum plot showing quantization noise, harmonic distortion and aliasing effects

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what Psychoacoustics is about

If you once listened to MPEG 1 Audio Layer 3 (aka mp3) compressed audio files you’ve already heard some encoding algorithms which are highly based on psychoacoustic principles. But what is that voodoo stuff all about in general? The science of psychoacoustics basically investigates the impact of a physical audio signals property on to the subjective perceived signal (hearing) and whats going on under the hood of that hearing, meanwhile. So it can basically be seen as an input/output model where a certain acoustic stimuli comes in and some sort of perception comes out. On top of that, hearing has not just been seen as a black box but a lot of modelling has already been done to get a better understanding on how hearing is actually performed in our bio-mechanical apparatus and our brain as well. [Read more…]