US 8,019,598 B2Granted

Phase locking method for frequency domain time scale modification based on a bark-scale spectral partition

AssigneeTexas Instruments Incorporated

InventorsAtsuhiro Sakurai, Steven Trautmann

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Abstract

This invention improves the perceived quality of frequency-domain time scale modification by selection of spectral bands used in phase locking based upon a Bark scale according to the variation in human hearing frequency response. A spectral peak is identified for each band. At these peaks the phases are rotated using the phase vocoder algorithm. For a few spectral lines near these peaks, the phase differences are copied from the non-rotated spectrum. The number selected is preferably 4. Remaining spectral lines within each spectral band located farther from the peak are phase rotated using the phase vocoder algorithm. The boundaries of the spectral bands may be adjusted based upon the digital audio data to maintain important frequency groups within the same spectral band.

Claims6

Dependent claims

A method of converting an input digital audio signal into an output digital audio signal having a modified time scale comprising the steps of:

receiving input digital audio data having a first time scale;
calculating a discrete Fourier transform of first equally spaced, overlapping time windows having a first overlap amount of the input digital audio signal;
partitioning the spectrum into a plurality of contiguous spectral bands according to a Bark scale where each spectral band has an extent dependent upon human frequency perception;
identifying a dominant spectral line having the greatest magnitude within each spectral band;
calculating a phase difference for the dominant spectral line of each spectral band by a phase vocoder algorithm;
calculating a phase difference for each of a predetermined number of spectral lines near the dominant spectral line within each spectral band as the phase difference of the corresponding dominant spectral line;
calculating a phase difference for other spectral lines of each spectral band by the phase vocoder algorithm;
calculating an inverse discrete Fourier transform resulting in equally spaced, overlapping time windows having a second overlap amount employing the calculated phase difference for each spectral line thereby producing the output digital audio signal, the second overlap selected having a ratio to the first overlap amount to achieve a desired time scale modification;
and
converting the output digital audio signal into sound having a second time scale according to the desired time scale modification.

7 more elements

A digital audio apparatus comprising:

a source of a digital audio signal;
a digital signal processor connected to said source of a digital audio signal programmed to perform time scale modification on the digital audio signal by
calculate a discrete Fourier transform of first equally spaced, overlapping time windows having a first overlap amount,
partition the spectrum into a plurality of contiguous spectral bands according to a Bark scale where each spectral band has an extent dependent upon human frequency perception,
identify a dominant spectral line having the greatest magnitude within each spectral band,
calculate a phase difference for the dominant spectral line of each spectral band by a phase vocoder algorithm,
calculate a phase difference for each of a predetermined number of spectral lines near the dominant spectral line within each spectral band as the phase difference of the corresponding dominant spectral line;
calculate a phase difference for other spectral lines of each spectral band by the phase vocoder algorithm, and
calculate an inverse discrete Fourier transform using equally spaced, overlapping time windows having a second overlap amount employing the calculated phase difference for each spectral line thereby forming a time scale modified digital audio signal, the second overlap selected having a ratio to the first overlap amount to achieve a desired time scale modification;
and
an output device connected to the digital signal processor for outputting the time scale modified digital audio signal.

8 more elements

Dependencies are inferred from the claim text.

Facts

Application: 10/714,174Filed 14 Nov 2003 · us provisional application
Priority: 15 Nov 2002
Published: US 2005/0010397 A113 Jan 2005
Granted: 13 Sep 2011
Term ends: Not estimatedThe source records don’t support an estimate.

Classification2 codes

G10L 21/04
Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its…:…
G10L
Speech analysis techniques or speech synthesis