Methods and apparatus to generate signatures representative of media
Example signature generation methods disclosed herein include transforming a block of signal samples from a time-domain representation to a frequency-domain representation including multiple frequency bands. Disclosed example signature generation methods also include fitting a signature function to at least a subset of the frequency bands. Disclosed example signature generation methods further include generating a set of signature values representative of the block of signal samples, the signature values generated based on a set of angles calculated using the signature function.
1. A signature generation apparatus comprising:
a transformer to transform a block of signal samples from a time-domain representation to a frequency-domain representation including multiple frequency bands;
a curve fitter to fit a signature function to at least a subset of the frequency bands; and
a generator to generate a set of signature values representative of the block of signal samples, the generator to generate the signature values based on a set of angles calculated using the signature function.
2. The apparatus of claim 1 , further including an angle calculator to calculate the set of angles using the signature function, the angle calculator to:
calculate a first one of the set of angles to be between a reference line and a first tangent line that is tangent to the signature function at a first index value in a set of index values over which the signature function is defined; and
calculate a second one of the set of angles to between the reference line and a second tangent line that is tangent to the signature function at a second index value in the set of index values.
3. The apparatus of claim 2 , further including an index selector to:
select the first index value; and
calculate the second index value based on a first value of the signature function at the first index value and a derivative of the signature function at the first index value.
4. The apparatus of claim 3 , wherein:
the index selector is further to calculate a third index value in the set of index values based on a second value of the signature function at the second index value and a derivative of the signature function at the second index value; and
the angle calculator is further to calculate a third one of the set of angles to be between the reference line and a third tangent line that is tangent to the signature function at the third index value.
5. The apparatus of claim 1 , wherein the set of angles are arranged as an order set of tuples, each tuple includes a plurality of angles, and the generator is to generate the set of signature values based on the tuples.
6. The apparatus of claim 5 , wherein the generator is to reduce respective ones of the tuples to respective single values to generate the set of signature values.
7. The apparatus of claim 6 , wherein the single values are binary values.
8. A signature generation method comprising:
transforming, by executing an instruction with a processor, a block of signal samples from a time-domain representation to a frequency-domain representation including multiple frequency bands;
fitting, by executing an instruction with the processor, a signature function to at least a subset of the frequency bands; and
generating, by executing an instruction with the processor, a set of signature values representative of the block of signal samples, the signature values generated based on a set of angles calculated using the signature function.
9. The method of claim 8 , further including calculating the set of angles using the signature function by:
calculating a first one of the set of angles to be between a reference line and a first tangent line that is tangent to the signature function at a first index value in a set of index values over which the signature function is defined; and
calculating a second one of the set of angles to between the reference line and a second tangent line that is tangent to the signature function at a second index value in the set of index values.
10. The method of claim 9 , further including:
selecting the first index value; and
calculating the second index value based on a first value of the signature function at the first index value and a derivative of the signature function at the first index value.
11. The method of claim 10 , further including:
calculating a third index value in the set of index values based on a second value of the signature function at the second index value and a derivative of the signature function at the second index value; and
calculating a third one of the set of angles to be between the reference line and a third tangent line that is tangent to the signature function at the third index value.
12. The method of claim 8 , wherein the set of angles are arranged as an order set of tuples, each tuple includes a plurality of angles, and the generating of the set of signature values is based on the tuples.
13. The method of claim 12 , wherein the generating of the set of signature values includes reducing respective ones of the tuples to respective single values to generate the set of signature values.
14. The method of claim 13 , wherein the single values are binary values.
15. A tangible computer readable storage medium comprising computer readable instructions which, when executed, cause a processor to at least:
transform a block of signal samples from a time-domain representation to a frequency-domain representation including multiple frequency bands;
fit a signature function to at least a subset of the frequency bands; and
generate a set of signature values representative of the block of signal samples, the signature values generated based on a set of angles calculated using the signature function.
16. The storage medium of claim 15 , wherein the instructions, when executed, further cause the processor to calculate the set of angles using the signature function by:
calculating a first one of the set of angles to be between a reference line and a first tangent line that is tangent to the signature function at a first index value in a set of index values over which the signature function is defined; and
calculating a second one of the set of angles to between the reference line and a second tangent line that is tangent to the signature function at a second index value in the set of index values.
17. The storage medium of claim 16 , wherein the instructions, when executed, further cause the processor to:
select the first index value; and
calculate the second index value based on a first value of the signature function at the first index value and a derivative of the signature function at the first index value.
18. The storage medium of claim 17 , wherein the instructions, when executed, further cause the processor to:
calculate a third index value in the set of index values based on a second value of the signature function at the second index value and a derivative of the signature function at the second index value; and
calculate a third one of the set of angles to be between the reference line and a third tangent line that is tangent to the signature function at the third index value.
19. The storage medium of claim 15 , wherein the set of angles are arranged as an order set of tuples, each tuple includes a plurality of angles, and the instructions, when executed, cause the processor to generate the set of signature values based on the tuples.
20. The storage medium of claim 19 , wherein the instructions, when executed, further cause the processor to generate the set of signature values by reducing respective ones of the tuples to respective single values to generate the set of signature values.