Pinpointing the Beat: Tapping to Expressive Performances.

1. Pinpointing the Beat: Tapping to Expressive Performances. By S. Dixon and W. Goebl (2002). (beat tracking & auto-transcription) Emilios Cambouropoulos (LBDM)

2. Outlines • Overview • Related work • Experiment Setup • Result I ~VI • Discussion & Conclusion

3. Overview • Tapping along with music • Beat tracking • Many models assume that beats correspond to the onset • Proposed Hypothesis: • The perception curve is smoother than the onset curve

4. Related Work • Finger tapping: constant rate vs synchronize (Madison, 2001) • Negative synchronization error: participants tend to tap earlier than the stimulus, about -20 and -60 ms (Wohlchlager & Koch, 2000) • What metrical level and at what phase listeners tend to synchronize with the music (Parncutt, 1994; Drake, Penel, Bigand, 2000; Snyder & Krumhansl, 2001) • Pianists tapped to different expressive performances. They tend to underestimate long IBIs, compensating for the error on the following tap (Repp, 1999)

5. ……………… K331:1 K284:1 K281:3 K331:1 Experiment Setup • Subject: • 25 Musically trained participants • Average of 19 years for playing their instruments • Stimuli– 4 excerpts, Each excerpt repeated 10 times 2-5 secs random duration gaps Total duration 13 minutes 45 seconds

6. Label Sonata Movt Bars Dur. p-IBI ML K331:1 K331 1st 1-8 25s 539ms 1/8 Stimuli – one excerpt Metrical Level 2nd bar p-IBI = (performed IBI)

7. ……………… K331:1 K284:1 K281:3 K331:1 Experiment Procedure => Recorded as t-IBI (tapped IBI) • Allowed participants to practice • Beats with no corresponding played notes were interpolated linearly • Matched each tap to the nearest played beat time • Deleting taps • 40% more than the average p-IBI • Matched to a beat already had a nearer tap

8. Results - I • Metrical levels are expressed as multiples of the default level • Two participants tapped on the 2nd and 4th quarter note beats of the bar • 3 failed tapping relate to participants tapping inconsistently – changing phase during the excerpt

9. Results - II Average synchronization time • Initial synchronization time: the first 3 successive beats which matched the calculated ML and phase • For each excerpt, tapers were able to synchronize on average by the third or fourth beat of the excerpt

10. Results - III p-IBI t-IBI K281:3 K331:1 • Solid line: t-IBI • Dotted line: p-IBI • The t-IBIs describe a smoother curve than the p-IBIs

11. Results - IV • To test the smoothing hypothesis more rigorously • The distance was measured by the RMS difference of the corresponding taps and beats (Cambouropoulos et al., 2001) • K331:1, The tempo curve is highly irregular due to relatively long pauses, which are used to emphasis the phrase structure • Based on tap-beat time (Time point) • Based on t-IBI and p-IBI (Interval)

12. Results - V Analysis of time lags of responses to tempo changes, measure of correlation of t-IBIs and p-IBIs • To find the time lag between tempo changes and changes in tapping rate • The lag of 1 tap is most common => participants respond to a tempo change on the tap after it occurs

13. Results - VI Analysis of time lags of responses to tempo changes – learning effect • It was expected that with repetition, the lag would decrease • With increasing repetitions, the 0 lag has the best correlation more frequently • For K284, no learning trend is seen • Authors’ comment: “it was like a chamber music rehearsal – you get it right after the third time”

14. Discussion & Conclusion • Perceived beat is smoother than the played notes • Anticipation: on-beats are perceived as anticipating • Minimal deviation: the perceptual system minimizes the deviation from strictly metrical time • The above implies that timing fluctuations are not necessarily perceived as tempo changes • Tapers underestimate timing changes • Two related test: • Listener preference test • Offline beat marking task