<div dir="ltr">I really enjoyed the aliasing-only example; someone should design a synth around it, really</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Feb 16, 2021 at 2:40 PM Richie Burnett <<a href="mailto:rburnett@richieburnett.co.uk">rburnett@richieburnett.co.uk</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I've uploaded some audio examples of what you can expect from these <br>
different synthesis techniques if anyone is interested:<br>
<br>
<a href="http://www.richieburnett.co.uk/temp/blep/" rel="noreferrer" target="_blank">http://www.richieburnett.co.uk/temp/blep/</a><br>
<br>
They all contain a Sawtooth waveform slowly swept from about 47Hz up to <br>
12kHz over a duration of 20 seconds...<br>
<br>
File "Saw_Naive" contains what you get if you just output the oscillator's <br>
phase accumulator directly at 48kHz. You get a Sawtooth with lots of <br>
aliasing. Most noticeable at the higher pitches though.<br>
<br>
File "Saw_PolyBLEP" contains what you get if you apply corrections to one <br>
sample before and one sample after each discontinuity using the PolyBLEP <br>
technique I mentioned, with 48kHz sample rate. This clearly sounds way <br>
better than just outputting the raw phase accumulator! But if you view the <br>
spectrum or spectrogram in something like Audacity or Goldwave you will see <br>
there's still plenty of aliasing going on at the top of the audio frequency <br>
range. You can actually watch harmonics bounce off the Nyquist limit (right <br>
edge of spectrum) and reflect back down. You can probably hear them too if <br>
you listen carefully.<br>
<br>
File "Saw_PolyBLEPx2" contains what you get if you run the same basic <br>
PolyBLEP technique with x2 oversampling (i.e. 96kHz sample rate). You still <br>
see some low-level aliasing right at the top end of the spectrum in <br>
Goldwave, but not much ventures into the region below the tone's <br>
fundamental. You will likely struggle to hear the aliasing now at sensible <br>
volume levels.<br>
<br>
File "Saw_BLEP16" contains a sawtooth synthesised using a full BLEP method <br>
correcting 16 samples around each discontinuity and running with x2 <br>
oversampling (96kHz.) Now you will see that the spectrum looks very clean <br>
everywhere right down to the noise-floor. (If you can hear aliasing in this <br>
file, then your PC or audio interface is likely performing some sort of <br>
sample-rate conversion, and doing it badly!)<br>
<br>
File "Saw_Aliases" contains just the corrections applied to the Naive Saw <br>
waveform around the discontinuities, just for fun. It essentially contains <br>
all of the aliased rubbish that gets removed by the BLEP algorithm, but you <br>
can hear it more clearly without the main Sawtooth tone masking it!<br>
<br>
As you can see the simple PolyBLEP method does a very good job of <br>
attenuating aliasing in the low-frequency region of the spectrum where it is <br>
most annoying, but the full BLEP technique tweaking several samples around <br>
each discontinuity gets close to perfection across the full audio spectrum.<br>
<br>
-Richie, <br>
<br>
<br>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature">Allt gott / Best wishes,<br>Mikael Altemark</div>