Method and system for sound source separation
Methods of sound source separation in which individual sources are extracted from a multiple source recording, include a method of analyzing stereo recordings to facilitate separation of individual musical sound sources from stereo music recordings. In the method sources predominant in the left are treated in a different manner to sources in the right.
1. A method of modifying a stereo recording for subsequent analysis, the stereo recording comprising a first channel signal and a second channel signal, the method comprising the steps of:
converting the first channel signal into the frequency domain,
converting the second channel signal into the frequency domain,
defining a set of scaling factors,
producing a frequency azimuth plane by
1) gain scaling the frequency converted first channel signal by a first scaling factor selected from the set of defined scaling factors,
2) subtracting the gain scaled first channel signal from the frequency converted second channel signal,
3) repeating steps 1) and 2) individually for the remaining scaling factors in the defined set to produce the frequency azimuth plane, the frequency azimuth plane representing magnitudes of different frequencies for respective scaling factors and which can be used for subsequent analysis.
2. A method of modifying a stereo recording according to claim 1 , wherein the step of producing the frequency azimuth plane comprises the further steps of
4) gain scaling the frequency converted second signal by the first scaling factor,
5) subtracting the gain scaled second signal from the frequency converted first signal,
6) repeating steps 4) and 5) individually for the remaining scaling factors in the defined set and combining the resulting gain scaled subtracted values with the previously determined gain scaled subtracted values in claim 1 to produce the frequency azimuth plane.
3. A method of analysing a stereo recording comprising the method of modifying the stereo recording according to claim 1 , the method of analyzing comprising the step of displaying a graphical representation of the produced frequency azimuth plane to a user.
4. A method of modifying a stereo recording according to claim 1 , further comprising the steps of determining a maximum value for each frequency in the frequency azimuth plane and subtracting individual frequency magnitudes in the frequency azimuth plane from the determined maximum values to produce an inverted frequency azimuth plane.
5. A method of analysing a stereo recording comprising the method of modifying the stereo recording according to claim 3 , further comprising the step of displaying a graphical representation of an inverted frequency azimuth plane to a user, the inverted azimuth plane being defined by determining a maximum value for each frequency in the frequency azimuth plane and subtracting individual frequency magnitudes in the frequency azimuth plane from the determined maximum values.
6. A method of extracting a sound source from a stereo recording comprising the: method of modifying a stereo recording according to claim 4 , the method of extracting comprising the step of applying a window to the inverted frequency azimuth plane to extract frequencies associated with a particular scaling factor.
7. A method of extracting a sound source from a stereo recording according to claim 6 , further comprising the step of converting the extracted frequencies into a time domain representation.
8. A method according to claim 1 , wherein said first channel signal is the LEFT signal in a stereo recording and said second channel signal is the RIGHT signal in the stereo recording or wherein said first channel signal is the RIGHT signal in a stereo recording and said second channel signal is the LEFT signal in the stereo recording.
9. A method according to claim 1 , wherein the defined set of scaling factors is in a range between 0 and 1 in magnitude.
10. A method according to claim 1 , wherein there is a uniform spacing between individual scaling factors.
11. A method of extracting a sound source from a stereo recording according to claim 7 , further comprising the step of applying a threshold filter to reduce noise prior to conversion into the time domain.
12. A method according to claim 1 , further comprising the initial step of breaking the first channel signal and the second channel signal into frames, wherein the individual steps of the method are then performed on a frame by frame basis.
13. A sound analysis system comprising:
an input module for accepting a first channel signal and a second channel signal,
a first frequency conversion engine being adapted to convert the first channel signal into the frequency domain,
a second frequency conversion engine being adapted to convert the second channel signal into the frequency domain, and
a plane generator being adapted to gain scale the frequency converted first channel signal by a series of scaling factors from a previously defined set of scaling factors, subtract the gain scaled frequency converted first channel signals from the frequency converted second signal, and combining the resulting scale subtracted values to produce a frequency azimuth plane which represents magnitudes of different frequencies for each of the scaling.
14. A sound analysis system according to claim 13 , wherein the input module comprises an audio playback device.
15. A sound analysis system according to claim 13 further comprising a graphical user interface for displaying the frequency azimuth plane.
16. A sound analysis system according to claim 14 , wherein the plane generator is further adapted to gain scale the frequency converted second signal by a first scaling factor selected from the set of defined scaling factors and to subtract the gain scaled frequency converted second channel signal from the frequency converted first channel signal and to repeat this individually for the remaining scaling factors in the defined set and to combine the resulting gain scaled subtracted values with the previously determined gain scaled subtracted values in claim 18 to produce the frequency azimuth plane.
17. A sound analysis system to claim 13 , further comprising first and second acoustic receivers, wherein the first channel signal and the second channel signal are each provided by the first and second acoustic receivers, respectively.
18. A system according to claim 17 , configured to switch a signal output between an output from the first and second acoustic receivers and an output from the sound analysis system.
19. A system for providing an audio signal output comprising a sound analysis system according to claim 17 .