Method and apparatus for changing the timbre and/or pitch of audio signals

• US 5,986,198 A
• Filed: 09/13/1996
• Issued: 11/16/1999
• Est. Priority Date: 01/18/1995
• Status: Expired due to Fees

• Current Assignee: IVL Audio Inc.
• Original Assignee: IVL Technologies, Ltd.
• Inventors: Roden, Brian John, Jubien, Christopher Michael, Gibson, Brian Charles
• Primary Examiner(s): DONELS, JEFFREY
• Application Number:
  US08/713,405
• Time in Patent Office: 1,159 Days
• Field of Search: 84/603-605, 84/619, 84/622, 84/659, 381/49, 395/2.14
• US Class Current: 84/603
• CPC Class Codes: G10H 1/20 for transposition
• CPC Class Codes: G10H 2210/066 for pitch analysis as part of wider processing for musical purposes, e.g. transcription, musical performance evaluation; Pitch recognition, e.g. in polyphonic sounds; Estimation or use of missing fundamental
• CPC Class Codes: G10H 2240/056 MIDI or other note-oriented file format
• CPC Class Codes: G10H 2250/285 Hann or Hanning window
• CPC Class Codes: G10H 2250/631 Waveform resampling, i.e. sample rate conversion or sample depth conversion waveform decimation G10H2250/611
• CPC Class Codes: G10H 3/125 Extracting or recognising the pitch or fundamental frequency of the picked up signal
• CPC Class Codes: G10H 5/005 Voice controlled instruments
• CPC Class Codes: G10H 7/08 by calculating functions or polynomial approximations to evaluate amplitudes at successive sample points of a tone waveform

Abstract

A method for shifting the timbre and/or pitch of an input signal samples the input signal at a first rate and stores the samples in a memory buffer. A digital signal processor resamples the stored input signal at a rate that differs from the first rate at which the input note is originally sampled and stores the resampled input signal in a second memory buffer. A pitch shifter shifts the pitch of the input signal by periodically scaling the resampled input signal by a window function to create an output signal. The rate at which the resampled data is replicated by the window function determines the pitch of the output signal.

Claims

1. An apparatus for producing a timbre shifted output signal from an input signal, comprising:

a digital memory;

a digital signal processor for receiving a digital representation of the input signal that has been sampled at a first rate and for storing the digital representation of the input signal in the digital memory;

means for resampling the digital representation of the input signal that is stored in the digital memory at a second rate that differs from the first rate, and for storing the resampled input signal in the digital memory;

a pitch shifter for creating a digital representation of the timbre shifted output signal by periodically extracting a segment of the resampled input signal and replicating the extracted segments at a rate equal to a fundamental frequency of the timbre shifted output signal;

wherein the pitch shifter extracts a segment of the resampled input signal by scaling the resampled input signal with a window function;

wherein the input signal and the timbre shifted output signal have a fundamental frequency and wherein the pitch shifter further comprises;

means for adjusting a duration of the window function based upon a difference between the fundamental frequency of the input signal and the fundamental frequency of the timbre shifted output signal;

wherein the means for adjusting the duration of the window function decreases the duration of the window if the fundamental frequency of the timbre shifted output signal is greater than the fundamental frequency of the input signal and increases the duration of the window function if the fundamental frequency of the timbre shifted output signal is less than the fundamental frequency of the input signal.

2. A system for creating a timbre shifted and/or pitch shifted output signal from an input signal, comprising:

means for receiving a digital representation of the input signal that has been sampled at a first rate;

means for receiving a reference note that defines a desired fundamental frequency of the timbre shifted output signal;

a comparator that analyzes the reference note and selects a resampling rate as a function of the analysis;

a digital signal processor that resamples the digital representation of the input signal at the selected resampling rate; and

a pitch shifter for creating the timbre shifted output signal by periodically extracting a segment of the resampled input signal and replicating the segments at a rate equal to the fundamental frequency of the reference note.

3. The system of claim 2, wherein the comparator analyzes the reference note by comparing the fundamental frequency of the reference note with one more thresholds.

4. The system of claim 2, further comprising:

means for determining a fundamental frequency of the input signal;

wherein the comparator analyzes the reference note by comparing the fundamental frequency of the reference note with the fundamental frequency of the input signal and selects the resampling rate as a function of the difference between the fundamental frequency of the reference note and the fundamental frequency of the input signal.

5. The system of claim 2, further comprising:

means for receiving a second reference note that defines a fundamental frequency;

wherein the comparator analyzes the reference note by comparing the fundamental frequency of the reference note with the fundamental frequency of the second reference note and selects the resampling rate as a function of the difference between the fundamental frequency of the reference note and the fundamental frequency of the second reference note.

6. A system for creating a timbre shifted and/or pitch shifted output signal from an input signal, comprising:

means for receiving a digital representation of the input signal that has been sampled at a first rate;

means for receiving a reference note that defines a desired fundamental frequency of the timbre shifted output signal;

means for calculating a length of time for which the input signal has been received;

a comparator that analyzes the length of time for which the input signal has been received and selects a resampling rate as a function of the length of time;

a digital signal processor that resamples the digital representation of the input signal at the selected resampling rate; and

a pitch shifter for creating the timbre shifted output signal by extracting a segment of the resampled input signal and replicating the segments at a rate substantially equal to the fundamental frequency of the reference note.

7. A system for creating a timbre shifted and/or pitch shifted output signal from an input signal, comprising:

means for receiving a digital representation of an input signal that has been sampled at a first rate;

means for receiving a reference note that defines a desired fundamental frequency of the timbre shifted output signal;

a comparator that analyzes a magnitude of the digital representation of the input signal and selects a resampling rate as a function of the magnitude;

a digital signal processor that resamples the digital representation of the input signal at the selected resampling rate; and

a pitch shifter for creating the timbre shifted output signal by periodically extracting a segment of the resampled input signal and replicating the segments at a rate substantially equal to the fundamental frequency of the reference note.

8. A method of creating a timbre shifted output signal from an input signal, comprising the steps of:

receiving a digital representation of said input signal consisting of a first set of values, wherein the first set has a first number of values;

storing said first set of values in a first memory buffer;

deriving from said first set a second set of values representative of said input signal, wherein the second set has a second number of values different from the first number, and storing said second set in a second memory buffer; and

replicating a portion of said second set at a rate equal to a fundamental frequency of said output signal to thereby produce said timbre shifted output signal.

9. The method of claim 8, wherein said digital representation is of a portion of said input signal and wherein the method includes the additional step of iterating the steps of claim 37 in relation to successive other portions of said input signal.

10. A method of creating a timbre shifted output signal from an input signal, comprising the steps of:

storing in a first plurality of memory locations a first set of values representative of a portion of said input signal, wherein the first set has a first number of values;

deriving from said first set a second set of values representative of said portion of said input signal, wherein the second set has a second number of values different from the first number of values, and storing said second set in a second plurality of memory locations; and

replicating a portion of said second set at a rate equal to a fundamental frequency of said output signal to thereby produce said timbre shifted output signal.

11. The method of claim 10, wherein the method includes the additional step of iterating the steps of claim 10 in relation to successive other portions of said input signal.

12. A method of creating a timbre shifted output signal from an input signal, comprising the steps of:

receiving a digital representation of a portion of said input signal that has been sampled at a first rate and resampling the digital representation at a second rate that differs from the first rate;

creating a digital representation of the timbre shifted output signal by replicating an extracted segment of the resampled digital representation at a rate equal to the fundamental frequency of the output signal; and

repeating the above steps in relation to another portion of said input signal.