DIRAC Time Stretching & Pitch Shifting

Whilst the majority of the recent work has involved a lot of planing and structuring of the tool application and its code base, I have also spent some time investigating the time stretching technique I intend to implement. Over the past few days it has become clear that I am unlikely to succeed in producing a time stretching algorithm capable of the tasks I would deligate to it. There are so many existing algorithms out there, each fairly complicated, that produce results of varying quality depending on the audio signal fed into them. For example the Rabiner and Schafer method does not work so well for polyphonic sounds but the phase vocoder method can introduce an audible after-effect known as "phase smearing".

However, I have come across a C/C++ library specially dedicated to pitch shifting and time stretching known as DIRAC. It comes in various flavours but their completly free DIRAC LE version interested me the most. This still provides the quality that you get with the studio and pro levels but puts some limits on things like supported sample rates and number of channels which don't really affect me too much.

DIRAC was developed by Stephan Bernsee, the founder of Prosoniq, and it can be seen in many professional level products such as Steinberg's Wavelab and Nuendo. It is an incredibly small and simple library containing a total of 7 functions and 3 enumerations, however the quality is astounding for it being a free product ( let's pretend we didn't see the 9870 EURO price tag for the full version ).

After a couple of days of tinkering I've managed to take a sound that's been loaded into FMOD and stretch/squash it using DIRAC. My test program is still a bit flaky though as I'm still not 100% sure how the sound buffers work. Doesn't help when FMOD works in bytes and DIRAC works in samples, but I'll get there.