This is a tweaknique that has a million uses, and is not MPC specific. As a matter of fact, on my MPC 2k I need to export a sample to an external editor and back for it to work... The idea came from an article written by Ethan Duni (from the Akai Mailing list) years ago.
The basic principle is to layer a sample with an inverted copy of itself. You then process the two samples individually, so that the inverted copy cancels out the original in various ways.
An example: On my 2k, I save a sample as wav, import it in to Cool Edit Pro (audio editor) and invert the waveform, and do no other processing before I save it and bring it back into the MPC.
Back in the box, I layer it with the original by letting one pad trigger two samples (remember to rename it to avoid it being replaced with the original sample). make sure the volume is set to the same level for both samples.
Now, in theory when you trigger the original and inverted samples together, you should hear nothing. I say in theory, because when you layer waveforms is this way they cancel each other out completely, resulting in total silence. This does not happen in the 2k because there is a latency of roughly 1 ms when triggering two samples from one pad - in some cases more when there is a lot of processing going on. To compensate for this you have to move the start point of the inverted copy about 30-40 samples back from the start point. In other words, you shorten it by 30-40samples. You will have to try a few different settings to find the one that has the most impact.
Small variations occur when triggering layered samples in the 2k, which you normally wouldn't hear, which is very notisable using this technique - this is why you will never find a spot where the two samples always cancel out completely. But don't despair...
When you have found a point where when you trigger both samples and they sometimes cancel each other out, resulting in silence when you hit the pad, filter one of them. The 2k has only a low pass filter, but when you use this trick, what you will hear is a slightly varying hi pass filter - varying because of the imperfect timing issues with the MPC. This is of course a good thing ... because it can be used to introduce timbral variations in your loops and kits.
If you are still with me, and you understand the principles behind phase cancellation, you will hopefully get some ideas of your own by now. Any filter will become it's own opposite - hi-pass turns into lo-pass, band-pass becomes notch, etc. Apply an envelope to the filter and more possibilities open up. And it dosn't stop with filters - try (very) small changes in pitch - this will cause the samples to drift out of phase with each other, and on short loops (as in 'looped in the trim page') this will produce a very nice tremolo effect.
A lot of experimentation is required but I can promise you that this pays off a hundredfold once you get your head around the idea - and of course anything that inverts phase is useful here, not just audio editors, but some desks have a phase reverse switch, as do mic preamps.
And try effects too! Chorus and reverb may not work too well, but don't take my word for it! If you are in to tweaking sounds, phase cancellation opens up a whole new can of worms!! In most cases, subtle changes to one waveform results in the biggest changes.
Start by processing only one sample if you have difficulties understanding what's actually going on (I know I do!).
Enjoy, and thanks for your tips - this is my first post but I think I'll be hanging out around here more from now on if that is alright for you guys...
