Music context system, audio track structure and method of real-time synchronization of musical content

1. A method of determining onsets in a digital audio signal having transient parts and relatively stationary parts, the method comprising:

separating transient parts from relatively stationary parts to produce a time domain representation of the transient parts, wherein said relatively stationary parts are frequencies that appear across consecutive sampling windows and transient parts are frequencies that demonstrate significant changes in energy in contiguous sampling windows where each sampling window has a duration of less than about 50 milliseconds;

generating an amplitude envelope of the transient part;

setting a power threshold and detecting localised peaks in the amplitude envelope that exceed the power threshold; and

from the localized peak, iterating backwards in time on a sample-by-sample basis over the duration of the sampling window to find a sampling point at which a measurable characteristic of the digital audio signal, measured during a first period having a first duration extending backwards in time before the sampling point, is maximally different from the measurable characteristic of the digital audio signal measured during a second period also having the first duration, the second period extending forwards in time from the sampling point; and

selecting as the position of the onset, the sampling point that is maximally different.

2. The method of determining the presence of an onset in accordance with claim 1 , wherein the step of identifying the onset corresponds to a largest measured power ratio between adjacent predetermined periods.

3. The method of determining the presence of an onset in accordance with claim 1 , wherein the characteristics includes a standard deviation of the first derivative of the transient signal before and after each sampling point.

4. The method of determining the presence of an onset in accordance with claim 1 , wherein the transient parts occur at relatively high frequencies in the audio signal.

5. The method of determining the presence of an onset in accordance with claim 1 , wherein the amplitude envelope is produced by applying a convolution function.

6. The method of determining the presence of an onset in accordance with claim 1 , wherein the sampling periods is between about ten milliseconds and about fifty milliseconds.

7. A computer program product that, when executed by a processor, causes the processor to execute procedure to determine the presence of an onset in a section of an audio signal, the procedure executing the method of any one of claims 1 to 6 .

8. An audio system comprising:

a processor; arranged:

for a digital audio file containing having transient parts and relatively stationary parts, to separate the transient parts from the relatively stationary parts to produce a time domain representation, wherein said relatively stationary parts are frequencies that appear across consecutive sampling windows and transient parts are frequencies that demonstrate significant changes in energy in contiguous sampling windows where each sampling window has a duration of less than about 50 milliseconds;

to generate an amplitude envelope of the transient parts;

to set a power threshold and detect a localised peak in the amplitude envelope that exceed the power threshold; and

from the localised peak, to iterate backwards in time on a sample-by-sample basis over the duration of the sampling window to find a sample point at which a measurable characteristic of the digital audio signal, measured during a first period having a first duration extending backwards in time before the sampling point, is maximally different from the measurable characteristic of the digital audio signal measured during a second period also having the first duration, the second period extending forwards in time from the sampling point; and

to select as the onset, the sample that is maximally different.

9. The audio system of claim 8 , wherein the first contextual theme is the same as the second contextual theme.

10. The audio system of claim 8 , wherein each onset is associated with an anacrusis that is related to a selected abstract exit point or abstract entry point in each digital audio file and where each anacrusis is a note or sequence of notes that precedes the first downbeat in a bar of music in each audio section, each anacrusis therefore representing the significant audio event.

11. The audio system of claim 8 , further comprising:

a database containing a multiplicity of digital audio files each partitioned into at least one audio section characterized by a contextual theme, each of said at least one audio sections having an onset representative of a significant audio event; and

the processor is arranged to use said identified onset to transition between a first contextual theme to a second contextual theme, the first contextual theme and the second contextual theme associated with at least one of said digital audio files that are stored within the database.

12. The audio system of claim 11 , wherein the processor is arranged to preserve integrity of musical timing in the transition between the first contextual theme and the second contextual theme.

13. The audio system of claim 11 , wherein the first contextual theme is the same as the second contextual theme.

14. The audio system of claim 11 , wherein the digital music files are stored in a database and the processor is arranged remotely to access the database over a network connection, the network connection supporting one of download and streaming of digital music files to the processor of a subscriber device.