Music – Instruments – Electrical musical tone generation
Reexamination Certificate
1999-08-20
2001-11-13
Witkowski, Stanley J. (Department: 2837)
Music
Instruments
Electrical musical tone generation
C084SDIG001
Reexamination Certificate
active
06316712
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the fields of tempo and beat detection where the tempo and the beat of an input audio signal is automatically detected. Given an audio signal, e.g. a .wave or .aiff file on a computer, or a MIDI files (e.g., as recorded on computer from a keyboard), the task is to determine the tempo of the music (the average time in seconds between two consecutive beats) and the location of the downbeat (the starting beat).
Various techniques have been described for detecting tempo. In particular, in a paper by E. D. Scheirer, entitled “Tempo and Bean analysis of acoustic musical signals”, J. Acoust. Soc. Am. 103 (1), January 1988, pages 588-601, a technique utilizing a bank or resonators to phase-lock with the beat and determine the tempo of the music is described. A paper by J. Brown entitled “Determination of the meter of musical scores by autocorrelation”, J. Acoust. Soc. Am. 94(4), October 1993, pages 1953-1957, describes a technique where the autocorrellation of the energy curve of a musical signal is calculated to determine tempo.
Research continues to develop effective, computationally efficient methods of determining tempo and locating beats.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an cross-correlation technique that is computationally efficient is utilized to determine tempo. A click track having windows located at transient times of an audio signal is cross-correlated with a series of pulses located at the transient times. A peak detection algorithm is then performed on the output of the cross-correlation to determine tempo.
According to another aspect of the invention, beat locations candidates are determined by evaluating the fit a series of pulses, starting at t
0
, with the click track. The fit is evaluated by perfoming a bi-directional search over inter-pulse spacing and the onset, t
0
, of the pulses.
According to another aspect of the invention, the downbeats are located in a musical interval having a variable tempo by dividing the musical segments and determining local tempos for each segment and downbeat candidates for each segment. The downbeat candidate in a following segment is selected which varies by the second tempo period from the last beat of a preceding segment.
According to another aspect of the invention, for musical intervals with sudden tempo changes, it is determined whether a tempo candidate is accurate.
According to a further aspect of the invention, the rhythm of an audio track is modified by rearranging or modifying segments of the track located between beats.
According to a further aspect of the invention, swing is added to an audio track by lengthening the intervals between some beats and shortening the intervals between other beats.
According to another aspect of the invention, the time-signature of the musical interval is changed by deleting the segments between some beats.
Additional features and advantages of the invention will be apparent in view of the following detailed description and appended drawing.
REFERENCES:
patent: 4419918 (1983-12-01), Dyck et al.
patent: 4694724 (1987-09-01), Kikumoto et al.
patent: 5256832 (1993-10-01), Miyake
patent: 5270477 (1993-12-01), Kawashima
patent: 5453570 (1995-09-01), Umeda et al.
patent: 5585586 (1996-12-01), Wakuda
patent: 5973255 (1999-10-01), Tanji
“Determination of the meter of musicl scores by autocorelation,” Brown,J. Acoust. Soc. Am. 94 (4) Oct. 1993.
“Tempo and beat analysis of acoustic musical signals,” Scheirer,J. Acoust. Soc. Am., 103 (1) Jan. 1998.
“Pulse Tracking with a Pitch Tracker,” Scheirer, Machine Listening Group, MIT Media Laboratory, Cambridge, MA 02139, 1997.
Creative Technology Ltd.
Townsend and Townsend / and Crew LLP
Witkowski Stanley J.
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