Data processing: speech signal processing – linguistics – language – Audio signal bandwidth compression or expansion
Reexamination Certificate
2000-05-11
2001-11-06
Dorvil, Richemond (Department: 2641)
Data processing: speech signal processing, linguistics, language
Audio signal bandwidth compression or expansion
C704S270000, C704S272000
Reexamination Certificate
active
06314403
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to digital signal processing techniques for producing a special effect during the playing of a digital signal. The present invention relates more particularly to digital signal processing techniques for producing a special effect by performing crossfading at both a micro and macro level for sequences of the digital signal.
BACKGROUND OF THE INVENTION
Digital audio workstations (DAWs) are increasingly popular in the recording studio and post-production environments. Digital audio workstations are used to mix, amplify, control and otherwise affect either the audio portion of a multimedia event or a production, which is solely audio, such as a song or composition. Two important features desirable in any DAW are the DAW's ability to perform audio “tasks” (such as equalization, reverberation, etc.) in a real-time, efficient manner and the ability of the DAW to edit a digital waveform to produce an interesting effect. Recently, digital audio workstations have been implemented using a personal computer, a PC, with specialized sound cards for capture and playback. Because of the processing capability of the PC, a digital waveform can be easily modified prior to playing back the signal. New sounds can be generated that are variations on the original audio. Alternatively, the signal can be “cleaned up” by digital processing techniques to eliminate imperfections in the original sound.
The production of a multimedia program typically involves editing an audio signal to augment the signal in some fashion. The editing of the signal is performed on digital samples generated after an Analog-to-Digital conversion of the analog audio signal. The resulting digital samples may be manipulated using digital signal processing (DSP) techniques to modify the signal in some interesting manner. For example, the playback speed of the stored audio data is changed to produce a new sound that is derived from the original audio. This change alters the duration of the playback sound. A side-effect of this manipulation is a pitch change, that is often referred to as the “chipmunk” effect because of the high pitch that results when voice is played back at high speeds. This pitch change results in an interesting special effect.
Special effects are not limited to only changes in the pitch of the audio, but include other modifications to the signal that produce interesting audio results. An effect typically results from numerically processing a digital representation of the original analog signal by modifying the digital values to produce the special effect. A further example of a special effect that can be generated digitally is a crossfade from one digital waveform to another waveform. The crossfading operation produces a transition between the two signals by phasing in the second waveform from the first waveform in a defined manner. The progression of the crossfade is usually specified by the user and can be adapted to generate a customized sound.
In the entertainment industry, the generation of innovative audio special effects has become increasingly important. Whether it is a sound recording by an artist or an audio/visual work such as a film, a production with unusual visual and audio effects enhances the marketability of the product. Consequently, it is important to discover interesting and novel effects that are efficiently implemented on a workstation such as a digital audio workstation.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for generating at a computerized workstation a special effect that is derived by numerical processing of the digital sample values associated with an analog signal.
In one aspect of the invention, a portion of the digital sample values is selected from the digital samples corresponding to the original analog signal, and partitioned into a first wavefragment and a second wavefragment.
In a further aspect of the invention, the first and second wavefragments are also partitioned into separate segments, and the separate segments for each of the wavefragments are crossfaded together to produce a micro special effect on the separate wavefragments.
In a yet further aspect of the invention, the partitioned segments for each of the wavefragments are crossfaded by summing corresponding weighted digital sample values from each of the partitioned segments for a particular wavefragment. In one practice of the invention, the weighted digital sample values are weighted according to a predetermined function. In one practice of the invention, the weighted digital sample values are weighted in a linearly increasing manner.
In a still further aspect of the invention, the result of the crossfaded segments for each wavefragment is crossfaded at a macro level with the crossfaded segments for the other wavefragment to produce a special effect. The wavefragments are crossfaded by summing corresponding weighted digital sample values from each of the wavefragments.
In a further aspect of the invention, the crossfade at the macro level is repeated by looping the crossfade operation to generate a predetermined frequency of crossfade. The frequency of crossfade may be a fractional frequency.
In a still further aspect of the invention, the analog signal may be an audio signal consisting of voiced or unvoiced audio. After the special effect, according to the invention, is digitally generated, the resulting digital values are input to a D/A converter to produce an analog signal corresponding to the special effect. The analog signal may drive audio speakers to generate an audio special effect.
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patent: 5824936 (1998-10-01), DuPuis et al.
patent: 5930755 (1999-07-01), Cecys
patent: 6098046 (2000-08-01), Cooper et al.
Goldenstein et al (“Time Warping of Audio Signals,” Computer Graphics International, Jun. 1999).
Avid Technology Inc.
Dorvil Richemond
Gordon Peter J.
Monks Lawrence E.
Nolan Daniel A.
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