Method of modifying harmonic content of a complex waveform

• US 7,003,120 B1
• Filed: 10/29/1999
• Issued: 02/21/2006
• Est. Priority Date: 10/29/1998
• Status: Expired due to Fees

• Current Assignee: Digital Harmonic LLC
• Original Assignee: Paul Reed Smith Guitars, Limited Partnership
• Inventors: Smith, Paul Reed, Smith, Jack W.
• Primary Examiner(s): Pendleton, Brian T.
• Application Number:
  US09/430,293
• Time in Patent Office: 2,307 Days
• Field of Search: 381/61, 846/26, 846/62, 847/01, 847/37, 846/97, 846/98, 846/99, 846/25
• US Class Current: 381/61
• CPC Class Codes: G10H 1/20 for transposition
• CPC Class Codes: G10H 1/383 Chord detection and/or recognition, e.g. for correction, or automatic bass generation
• CPC Class Codes: G10H 1/44 Tuning means
• CPC Class Codes: G10H 2210/335 Chord correction, i.e. modifying one or several notes within a chord, e.g. to correct wrong fingering or to improve harmony natural chords G10H2210/586
• CPC Class Codes: G10H 2210/471 Natural or just intonation scales, i.e. based on harmonics consonance such that most adjacent pitches are related by harmonically pure ratios of small integers pitch correction only when playing chords to ensure chord consonance G10H2210/586
• CPC Class Codes: G10H 2210/581 Chord inversion
• CPC Class Codes: G10H 2210/586 Natural chords, i.e. adjustment of individual note pitches in order to generate just intonation chords scale natural G10H2210/471; chord correction G10H2210/335; musical analysis G10H2210/031
• CPC Class Codes: G10H 2210/596 Chord augmented
• CPC Class Codes: G10H 2210/601 Chord diminished
• CPC Class Codes: G10H 2210/621 Chord seventh dominant
• CPC Class Codes: G10H 2210/626 Chord sixth
• CPC Class Codes: G10H 2250/161 Logarithmic functions, scaling or conversion, e.g. to reflect human auditory perception of loudness or frequency
• CPC Class Codes: G10H 3/125 Extracting or recognising the pitch or fundamental frequency of the picked up signal
• CPC Class Codes: G10H 3/186 Means for processing the signal picked up from the strings filtering G10H1/12

Abstract

A method of manipulating a complex waveform by considering the harmonic and partial frequencies as moving targets over time in both amplitude and frequency and adjusting the moving targets by moving modifiers in both amplitude and frequency. The manipulation of harmonic frequencies and the synthesis of harmonic frequencies are based on the harmonic rank. The modifiers move with the movement of the frequencies based on rank. Harmonic transformation modifies, by rank, the waveform from one source to a waveform of a second or target source. Harmonics and other partials accentuation identifies each of the frequencies and its relationship to adjacent frequencies as well as fixed or moving thresholds and make the appropriate adjustment. Interpolation is also disclosed as well as models which imitate natural harmonics.

Claims

1. A method of modifying the amplitudes of harmonics of a detected tone spectrum in a complex waveform, the method comprising:

determining a dynamic energy threshold, as a function of frequency, from detected energy of partials;

continually determining an amplitude modification for each selected rank of the harmonics relative to the threshold; and

applying the determined modification with an amplitude modifying function to each harmonic of the detected tone spectrum selected by harmonic rank, where the frequency associated with each amplitude modifying function is continually set to the frequency corresponding to the harmonic rank as the frequencies of the detected tone spectrum containing the selected harmonics change over time.

2. The method according to claim 1, wherein the amplitude modifying functions are adjustable with respect to at least one of frequency and amplitude.

3. The method according to claim 1, including assigning a harmonic rank to each amplitude modifying function and setting the frequency of the amplitude modifying function to the frequency of the harmonic of that rank as the frequency of the harmonic changes.

4. The method according to claim 3, including assigning an amplitude change to each amplitude modifying function.

5. The method according to claim 1, wherein the amplitude modifying functions are set to fixed frequencies;

applying the amplitude modifying function to a selected harmonic when the frequency of the amplitude amplifying function and the harmonic correspond; and

adjusting the amplitude modification of the amplitude modifying function as a function of the selected rank of the harmonics.

6. The method according to claim 1, including using the methods of Fast Find Fundamental to determine the ranks of the harmonic frequencies of the detected tone spectrum.

7. The method according to claim 1, including determining which partials are harmonics of a harmonic tone spectrum and their harmonic ranks using the methods of Fast Find Fundamental.

8. The method according to claim 1, wherein the amplitude modifying function varies in frequency and amplitude with time.

9. The method according to claim 1, including comparing a first selected harmonics amplitude to a second selected harmonics amplitude within the same tone spectrum and adjusting the first harmonics amplitude relative to the second selected harmonics amplitude based on the comparison and rank.

10. The method according to claim 1, including using the amplitude modifying function to synthesize harmonics of selected harmonic ranks and adding the synthesized harmonic frequencies to the waveform.

11. The method according to claim 10, wherein the harmonics are synthesized using a modeling function f_n=f₁×

n×

S^log₂ⁿ, where S is a constant greater than 1 and n is the rank of the harmonic.

12. The method according to claim 1, including using the amplitude modifying function to synthesize selected inharmonicities and adding the synthesized inharmonicities to the waveform.

13. The method according to claim 1, wherein the amplitude modifying function includes modifying detected partials of the complex waveform by frequency, amplitude, and time and by harmonic rank to resemble a second source complex waveform.

14. The method according to claim 1, wherein the amplitude modifying function includes synthesizing selected partials of the complex waveform by frequency, amplitude, and time and by harmonic to resemble a second source complex waveform.

15. The method according to claim 1, including setting two or more frequency based parameters;

selecting an interpolation function; and

adjusting the amplitudes of harmonics based on the frequency based parameters and interpolation function.

16. The method according to claim 1, including:

setting a noise floor threshold as a function of frequency.

17. The method according to claim 16, wherein setting the noise floor threshold as a function of frequency is performed continuously.

18. The method according to claim 17, wherein the noise floor threshold is set as a function of time.

19. The method according to claim 1, wherein the amplitude modifying functions are processed using mathematical models, algorithms, or functions.

20. The method according to claim 1, wherein the amplitude modification changes with the selected rank of harmonic'"'"'s frequency as the selected rank of harmonic'"'"'s frequency changes over time.

21. The method according to claim 1, wherein the frequency of each amplitude modifying function is continuously set to the frequency corresponding to the selected rank of harmonic'"'"'s frequency as the frequency of the selected rank of harmonic changes over time.

22. The method according to claim 1, wherein the dynamic energy threshold is determined from the detected energy of adjacent partials.

23. The method according to claim 1, wherein the dynamic energy threshold is determined from the detected partial'"'"'s energy and frequency within a time period.

24. The method according to claim 1, wherein the dynamic energy threshold is determined as an average of the detected energy of all of the partials.

25. The method according to claim 1, wherein the dynamic energy threshold is determined for each partial from partial'"'"'s energy within a frequency band of that partial within a time period.

26. The method according to claim 1, wherein the selected rank of harmonic'"'"'s amplitude modification is determined by that selected rank of harmonic'"'"'s amplitude over time and its relation to the thresholds during that time period.

27. The method according to claim 1, wherein selected ranks of harmonics whose energy is above the dynamic energy threshold is adjusted using a scaling function.

28. The method according to claim 1, wherein selected ranks of harmonics whose energy is below the dynamic energy threshold is adjusted using a scaling function.

29. The method according to claim 1, including determining a second dynamic energy thresholds as a function of frequency from the detected energy of the partials.

30. The method according to claim 1, including setting a maximum clipping threshold.

31. The method according to claim 1, wherein the scaling functions are scaled when the threshold levels changes.

32. The method according to claim 16, including not adjusting the amplitude of selected ranks of harmonics having an amplitude less than the noise floor threshold.

33. The method according to claim 1, wherein the selected ranks of harmonic'"'"'s energies must meet amplitude thresholds for a set time duration before the selected ranks of harmonics are adjusted in amplitude.

34. The method according to claim 33, wherein the time duration may vary.

35. The method according to claim 1, wherein the amplitude modifying function is accomplished using frequency &

amplitude adjustable digital filtering methods.

36. The method according to claim 1, wherein the amplitude modifying function is accomplished using fixed frequency, variable amplitude filters processing methods.

37. The method according to claim 1, including storing the method as instructions in a digital signal processor.

38. The method according to claim 37, including passing the detected tone spectrum through a delay buffer.

39. The method according to claim 37, including initially passing the complex waveform through an A/D converter.

40. The method according to claim 1, including storing the complex waveform;

and determining over time the tone spectra and its harmonic'"'"'s frequencies, amplitudes, and harmonic ranks.

41. A machine for performing the method of claim 1.

42. A list of instructions fixed in a machine readable media for performing the method of claim 1.

43. A method of modifying the amplitudes of harmonics of a detected tone spectrum in a complex waveform, the method comprising:

determining a modification to selected ranks of the harmonics based on the frequency and energy of the harmonic relative to detected energy of partials of the detected tone spectrum; and

applying the determined modification with an amplitude modifying function to each harmonic of the detected tone spectrum selected by harmonic rank, where the frequency associated with each amplitude modifying function is continually set to the frequency corresponding to the harmonic rank as the frequencies of the detected tone spectrum containing the selected harmonics change over time.