Method and system for comparing audio signals and identifying an audio source
A method for defining an index of a match between a content of two audio sources, comprising: sampling audio from a first source and a second source generating a first and second set of samples; selecting a sequential number of samples N belonging to the first set of samples and N samples belonging to the second set; transferring the first and second sequences of N samples to the frequency domain, generating a first and second sequences of N/2 frequency intervals; for the first sequence, calculating the sign of the derivative; for the second sequence, calculating the sign and the absolute value of the derivative, and a total sum of the absolute values of the derivative and a partial sum of the absolute values of the derivative; the ratio between the partial sum and the total sum being an index of the match of the audio sources.
1. A method for defining an index of a match between a content of two audio sources, comprising the steps of:
a) defining a set of sampling parameters;
b) sampling audio from a first source according to said sampling parameters, generating a first set of samples, and audio from a second source according to said sampling parameters, generating a second set of samples;
c) selecting a sequential number of samples N which belong to said first set of samples and an identical number of samples N to be compared which belong to said second set of samples;
d) transferring said first sequence of N samples to the frequency domain, generating a first sequence of N/2 frequency intervals, and transferring said second sequence of N samples to the frequency domain, generating a second sequence of N/2 frequency intervals;
for said first sequence of N/2 frequency intervals, calculating the sign of the derivative;
e) for said second sequence of N/2 frequency intervals, calculating the sign of the derivative and the absolute value of the derivative and calculating a total sum constituted by the sum of the absolute values of the derivative in each frequency interval comprised between a lower limit and an upper limit;
f) for said second sequence of N/2 frequency intervals, calculating a partial sum constituted by the sum of the absolute values of the derivative in each frequency interval comprised between a lower limit and an upper limit, wherein the sign of the derivative in the frequency interval that belongs to said second sequence coincides with the sign of the derivative of the corresponding frequency interval in said first sequence;
g) using the ratio between said partial sum and said total sum as an index of the match of said content of said audio sources.
2. The method according to claim 1 , wherein said sampling parameters include: the sampling frequency and the number of bits per sample.
3. The method according to claim 2 , wherein said sampling frequency is equal to 6300 Hz.
4. The method according to claim 2 , wherein said number of bits per sample is equal to 16.
5. The method according to claim 1 , wherein said first audio source is an ambient sound recording.
6. The method according to claim 1 , wherein said second sound source is a radio or television station.
7. A system for comparing a content of two audio sources, comprising:
a) sampling means for sampling audio from a first source according to sampling parameters, generating a first set of samples, and audio from a second source according to said sampling parameters, generating a second set of samples;
b) means for transforming in the frequency domain a sequential number of samples N which belong to said first set of samples and an equal number of samples N to be compared, which belong to said second set of samples, generating a first sequence of N/2 frequency intervals and a second sequence of N/2 frequency intervals;
c) means for calculating, for each frequency interval of said first sequence, the sign of the derivative and for calculating, for said first sequence of N/2 frequency intervals, the sign of the derivative, the absolute value of the derivative and a total sum constituted by the sum of the absolute values of the derivative in each frequency interval comprised between a lower limit and an upper limit;
d) means for calculating, for said second sequence of N/2 frequency intervals, a partial sum constituted by the sum of the absolute values of the derivative in each frequency interval comprised between a lower limit and an upper limit, if the sign of the derivative in the frequency interval that belongs to said second sequence coincides with the sign of the derivative of the corresponding frequency interval in said first sequence;
e) means for determining the ratio between said partial sum and said total sum in order to obtain an index of the match of said content of said audio sources.
8. The system according to claim 7 , wherein said sampling parameters include: the sampling frequency and the number of bits per sample.
9. The system according to claim 8 , wherein said sampling frequency is 6300 Hz.
10. The system according to claim 8 , wherein said number of bits per sample is 16.
11. The system according to claim 7 , further comprising interface means for recording the data of a radio or television station.
12. The system according to claim 7 , further comprising a portable data acquisition device for said first audio source.
13. A portable device for recording ambient sounds for a system according to claim 7 .