Audio signal analysing method and apparatus

1 . A method for determining the key of an audio signal, the method comprising the steps of:

for each of a plurality of signal portions, analysing the portion to identify [p v1]a musical note, and where at least one musical note is identified:

determining a strength associated with the or each musical note; and

generating a data record containing the identity of the or each musical note, the strength associated with the or each musical note and the identity of the portion;

for each of the data records, ignoring the strength associated with an identified musical note where said strength is less than a predetermined fraction of the maximum strength associated with any identified musical note contained within the data records;

determining a first note from the identified musical notes as a function of their respective strengths;

selecting at least a second and a third note from the identified musical notes as a function of the first note; and

determining the key based on a comparison of the respective strengths of the at least second and third notes.

2 . A method as claimed in claim 1 , wherein each portion is the same size.

3 . A method as claimed in claim 1 , wherein each portion encompasses the same length of time.

4 . A method as claimed in claim 1 , wherein the size of the portion is a function of the tempo of the audio signal.

5 . A method as claimed in claim 1 , wherein the portions are contiguous.

6 . A method as claimed in claim 1 , wherein the predetermined fraction is determined in dependence on the content of the audio signal.

7 . A method as claimed in claim 1 , wherein the predetermined fraction lies in the range of one tenth to one half.

8 . A method as claimed in claim 7 , wherein the predetermined fraction is one seventh.

9 . A method as claimed in claim 1 , wherein the step of analysing the portion to identify a musical note comprises the steps of:

converting the portion to a frequency domain representation;

subdividing the frequency domain representation into a plurality of octaves;

for each octave containing a maximum amplitude:

determining a frequency value at the maximum amplitude; and

selecting a note name of a musical scale in dependence on the frequency value;

and

identifying a musical note in dependence on the same note name being selected in more than one octave.

10 . A method as claimed in claim 9 , wherein the conversion of the portion to a frequency domain representation is performed by means of a Fourier Transform.

11 . A method as claimed in claim 9 , wherein the musical scale is the Equal Tempered Scale.

12 . A method as claimed in claim 1 , wherein the step of determining a strength associated with the or each musical note comprises the steps of:

determining the amplitude of each frequency component of the musical note; and

summing the amplitudes.

13 . A method as claimed in claim 1 , wherein the step of determining the first note comprises the steps of:

for each identified musical note, summing the strengths associated with the musical note in the data records; and

determining the first note to be the identified musical note with the maximum summed strength.

14 . A method as claimed in claim 1 , wherein the first note is the tonic of the key.

15 . An apparatus for determining the key of an audio signal, the apparatus comprising:

an input device operable to receive a signal;

a data processing apparatus operable to:

for each of a plurality of signal portions, analyse the portion to identify [p v2]a musical note, and where at least one musical note is identified:

determine a strength associated with the or each musical note; and

generate a data record containing the identity of the or each musical note, the strength associated with the or each musical note and the identity of the portion;

for each of the data records, ignore the strength associated with an identified musical note where said strength is less than a predetermined fraction of the maximum strength associated with any identified musical note contained within the data records;

determine a first note from the identified musical notes as a function of their respective strengths;

select at least a second and a third note from the identified musical notes as a function of the first note; and

determine the key based on a comparison of the respective strengths of the at least second and third notes.

16 . An apparatus as claimed in claim 15 , wherein the predetermined fraction is determined in dependence on the content of the audio signal.

17 . An apparatus as claimed in claim 16 , wherein the predetermined fraction lies in the range of one tenth to one half.

18 . An apparatus as claimed in claim 17 , wherein the predetermined fraction is one seventh.

19 . An apparatus as claimed in claim 15 , wherein for each of a plurality of signal portions, to analyse the portion to identify a musical note the data processing apparatus is operable to:

convert the portion to a frequency domain representation;

subdivide the frequency domain representation into a plurality of octaves;

for each octave containing a maximum amplitude

determine a frequency value at the maximum amplitude; and

select a note name of a musical scale in dependence on the frequency value;

and

identify a musical note in dependence on the same note name being selected in more than one octave.

20 . An apparatus as claimed in claim 19 , wherein the data processing apparatus is operable to convert the portion to a frequency domain representation by performing a Fourier Transform.

21 . An apparatus as claimed in claim 19 , wherein the musical scale is the Equal Tempered Scale.

22 . An apparatus as claimed in claim 15 , wherein to determine a strength associated with the or each musical note the data processing apparatus is operable to:

determine the amplitude of each frequency component of the musical note; and

sum the amplitudes.

23 . An apparatus as claimed in claim 15 , wherein to determine the first note the data processing apparatus is operable to:

for each identified musical note, sum the strengths associated with the musical note in the data records; and

determine the first note to be the identified musical note with the maximum summed strength.

24 . An apparatus as claimed in claim 15 , further comprising an output device operable to send data corresponding to the key of the audio signal.

25 . A record carrier comprising software operable to carry out the method of claim 1 .

26 . A software utility configured for carrying out the method steps as claimed in claim 1 .

27 . A jukebox including a data processor, said data processor being directed in its operations by a software utility as claimed in claim 26 .

28 . A method for determining the key of an audio signal substantially as hereinbefore described and with reference to the accompanying drawings.

29 . An apparatus for determining the key of an audio signal substantially as hereinbefore described and with reference to the accompanying drawings.