Music 209 Week 4: Time-Warping and Beat-Matching

February 9, 2006.

Concatenation of two rhythmic units may require the tempos to match. We describe techniques for matching tempos without otherwise altering units.

Topics

The lecture covered beat-slicing and overlap-add techniques for time-warping. We began with a description of Drumcore, a drumloop system that handles tempo changing by recording real drummers playing at many different tempos. This review describes how Drumcore works.

We then discussed beat-slicing. Good tutorials on beat splicing are available here and here. We also discussed the beat-slicing implementation in Pro Tool's Beat Detective feature. A good tutorial on Beat Detective is available here.

We then turned our focus to overlap-add methods of time warping. We began by noting that professional use of these algorithms dates back to the 1980 (Lexicon 2400). This webpage and this webpage describe the overlap-add methods used in the Lexicon 2400.

We then described the mechanics of overlap-add methods in detail. This tutorial was adapted from Chapter 2 of Jordi Sanhaume's Ph.D. thesis, available for download here.

The SOLA examples we played in class used the PICOLA algorithm. This algorithm is described in Annex 5.D (page 128) of this document. To play with this algorithm, try out the speedt SAOL core opcode as implemented in sfront.

We ended the lecture with an idea for a class project based on this archive of George Bush speeches.

Finally, this website provides a good comparative analysis of time-warping methods.