Audio time stretch method and associated apparatus

1. A method for audio time stretch implemented by an executable program stored in a non-transitory computer-readable storage medium to instruct a microprocessor of an apparatus for audio time stretch, comprising:

receiving a plurality of first audio data and a plurality of second audio data;

calculating an energy level according to amplitudes of the first data;

selectively performing a waveform search for the first audio data according to the energy level for waveform similarities;

duplicating a section of an audio data to extend an audio output according to a search result where an audio repository is smaller than a water level;

wherein the step of selectively performing the waveform search comprises:

selecting a plurality of third audio data from the first audio data as removable audio data according to waveform similarities in the first audio data; and

selecting a plurality of fourth audio data from the first audio data as addible audio data according to waveform similarities in the first audio data.

2. The method according to claim 1 , further comprising:

performing the waveform search when the energy level is smaller than a threshold; and

stopping the waveform search when the energy level is greater than the threshold.

3. The method according to claim 2 , further comprising:

updating the threshold according to the energy level of said plurality of second audio data; and

selectively performing the waveform search for the second audio data according to whether amplitudes of the second audio data are smaller than the updated threshold.

4. The method according to claim 1 , wherein the step of selectively performing the waveform search further comprises:

setting a removable flag as an enable value for the removable audio data in the first audio data.

5. The method according to claim 4 , further comprising:

checking a repository; and

removing the removable audio data from the first audio data when the repository is greater than said water level and the removable flag matches the enable value.

6. The method according to claim 5 , wherein the step of selectively performing the waveform search comprises:

setting an addible flag as an enable value for the addible audio data in the first audio data.

7. The method according to claim 6 , wherein the step of duplicating audio data comprises:

checking a repository; and

duplicating the addible audio data when the addible flag matches the enable value.

8. An apparatus, including a non-transitory computer-readable storage medium with an executable program stored thereon, wherein said executable program instructs to perform audio time stretch, comprising:

an energy level module, for calculating an energy level according to amplitudes of a plurality of first audio data and a plurality of second audio data;

a determining module, coupled to the energy level module, for determining whether to perform a waveform search among the first audio data according to the energy level to output a determination result; wherein said determining module duplicates a section of an audio data to extend an audio output according to a search result where an audio repository is smaller than a water level; and

a waveform search module, coupled to the determining module;

wherein the waveform search module selects a plurality of third audio data from the first audio data as removable audio data according to waveform similarities in the first audio data, and the waveform search module selects a plurality of fourth audio data as addible audio data from the first audio data according to waveform similarities in the first audio data.

9. The apparatus according to claim 8 , wherein said waveform search module selectively performs the waveform search according to the determination result.

10. The apparatus according to claim 9 , further comprising:

a threshold module, for providing a threshold;

wherein, the determining module compares the energy level with the threshold, and the waveform search module performs the waveform search among the first audio data when the energy level is smaller than the threshold and stops the waveform search when the energy level is greater than the threshold.

11. The apparatus according to claim 10 , wherein when the energy level module calculates a second energy level according to amplitudes of said plurality of second audio data, the threshold module updates the threshold according to the energy level, and the determining module compares the second energy with the updated threshold to determine whether the waveform search module performs the waveform search among the second audio data.

12. The apparatus according to claim 9 , further comprising a flag register for recording a removable flag; wherein, the removable flag is set as an enable value for the removable audio data.

13. The apparatus according to claim 12 , further comprising a buffer control module for checking an audio repository; wherein, the buffer control module removes the removable audio data from the first audio data when the audio repository is greater than a water level and the removable flag matches the enable value.

14. The apparatus according to claim 9 , further comprising a flag register for recording an addible flag; wherein, the addible flag is set as an enable value for the addible audio data.

15. The apparatus according to claim 14 , further comprising a buffer control module for checking an audio repository; wherein, the buffer control module inserts the addible audio data to the first audio data when the audio repository is smaller than a water level and the addible flag matches the enable value.

16. The method according to claim 1 , wherein the waveform search comprises a waveform similarity based synchronized overlap-add (WSOLA) algorithm.

17. The apparatus according to claim 8 , wherein the waveform search comprises a waveform similarity based synchronized overlap-add (WSOLA) algorithm.