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[Din]

I've got an IT 2.14 mod that's been in the works for about 4 years and have just recently finished.  I was all set to release it when I decided to wear it out on my CD walkman and came face to face with that dreaded foe...aliasing.  It's very subtle for the most part, but it's definitely there rattling away in the mix.  I've nailed down the culprits to 3 samples I recorded from my copy of the MTV Music Generator for PS1 (which will simply require rerecording to correct) and 1 looped, otherwise well-behaved preset exported from Paul's Sound Designer 2.2 for DOS.

My question is this:  can bad loop points cause aliasing? 

This problem just appeared out of nowhere.  Until now I've only had to deal with clicking, but this is a new one.  What bothers me most is that I can't really hear any aliasing (or not much) while playing it back in IT (due to linear interpolation?), even on my good speakers (M-Audio Studio Pro 4s...overkill for IT I know, but very nice ).  I only heard it after I'd transferred it from my DOS box over to my XP machine and exported it as a WAV with XMPlay.  That's a bit of tedious work only to find out afterwards that my samples are misbehaving.

But my question is more academic than anything.  Has anyone run into this problem before?
Curiouser and curiouser...

[fingersoup]

Well, I've seen a number of things....  If your loop is too small, it can affect the pitch of your loop point.  If the loop has a gradual change in pitch or volume (up or down) it can create a buzzing or warbling sound similar to aliasing (I'm not 100% up on the technical requirements of calling it aliasing).  Whether it technically is or not, I'm not sure...  One could make the arguement either way

You see, aliasing is most notably caused by resampling (ie Digital distortion).  Every example I've looked at says it is re-sampling related.  It's that tinny sound on Cymbals that you hear in the MP3 you just ripped from CD. Nothing really states it includes looping points (probably because most people don't loop samples in the same way trackers do).

On the other hand, there are some leanings that filters and envelopes can cause aliasing....  If 2 components are out of sync - ie the peaks of your loop's waves are every 100 samples, but your interpolation filter uses a window of 96 samples to do it's math (anything not a multiple or product of 100), Audible errors may be introduced.  THOSE audible noises in pitch/distortion/etc... would be the effect of aliasing, and may sound different than straight resampling aliasing (lowering bitrate, etc).

Given the above example of filtering, Some people might call the pops and clicks you mention a form of aliasing.  You've created a loop point that introduces a noise or distortion due to mismatched timing. 

Regardless, here's some suggestions.  Try making your loop larger if possible, or if that doesn't work, and you can find a good sample point for a ping-pong loop (Making sure your tracker supports this) try using one. 

[Din]

Actually, I was referring to the clicking associated with poorly matched loop points, where the amplitudes don't meet.  I've also encountered samples changing pitch in really short loops, but the looped sample that's giving me grief is several hundred kilobytes long, with a forward loop starting in the last third.

I'll give the ping-pong loop a try, though.  If that doesn't work, I'll have to see what I can do with Paul's Sound Designer export options.  Who knows, my sample might just have gotten corrupted.  Scandisk and Defrag to the rescue.

Thanks for the help.