Time-scale modification of data-compressed audio information
A data-compressed audio waveform is temporally modified without requiring complete decompression of the audio signal. Packets of compressed audio data are first unpacked, to remove scaling that was applied in the formation of the packets. The unpacked data is then temporally modified, using one of a number of different approaches. This modification takes place while the audio information remains in a data-compressed format. New packets are then assembled from the modified data, to produce a data-compressed output stream that can be subsequently processed in a conventional manner to reproduce the desired sound. The assembly of the new packets employs a technique for inferring an auditory model from the original packets, to requantize the data in the output packets.
1. A method for temporally modifying an audio waveform comprising:
receiving input data associated with the audio waveform;
obtaining input samples, wherein the input samples are in a data compressed format;
selecting input samples for creating output samples, wherein the output samples are in a data compressed format; and
creating output data associated with a temporally modified audio waveform using the output samples.
2. The method of claim 1 wherein creating output data includes the selective omission of a number of samples.
3. The method of claim 2 wherein the number of omitted samples is based at least in part on the content of data in an input packet.
4. The method of claim 1 wherein creating output data includes shifting frequencies associated with one or more samples.
5. The method of claim 1 wherein creating output data includes the duplication of one or more samples.
6. The method of claim 1 wherein obtaining input samples includes undoing magnitude scaling.
7. The method of claim 1 wherein creating output data includes rescaling one or more samples.
8. The method of claim 1 wherein the input data is in MPEG format.
9. The method of claim 1 wherein the temporal modification is temporal compression of the audio waveform.
10. The method of claim 1 wherein the temporal modification is temporal expansion of the audio waveform.
11. The method of claim 1 wherein selecting input samples includes dividing the input samples into groups of consecutive input samples.
12. The method of claim 1 wherein the output samples are groups of consecutive input samples copied a plurality of times.
13. The method of claim 1 further comprising forming a hypotheses of quantization levels.
14. The method of claim 1 wherein the input data is compressed in a format which divides samples into different subbands in the spectral range of the audio waveform.
15. The method of claim 1 wherein the input data is compressed in accordance with a perceptual model.
16. The method of claim 1 wherein selecting input samples includes dividing the input samples into groups of consecutive input samples such that the size of the groups is a higher valued divisor of 72/N where N:1 temporal compression is being performed.
17. The method of claim 1 further comprising:
low pass filtering and downsampling the input sample from selected input frequency subband i to obtain the output sample for output frequency subband 2i; and
high pass filtering and downsampling the input sample from selected input frequency subband i to obtain the output sample for output frequency subband (2i+1).
18. The method of claim 1 further comprising:
upsampling and low pass filtering the input sample from selected input frequency subband 2i;
upsampling and high pass filtering the input sample from selected input frequency subband (2i+1); and
summing the two upsampled and filtered results to obtain the output sample for output frequency subband i.
19. A system for temporally modifying an audio waveform, including:
a processor; and
a memory coupled with the processor, wherein the memory is configured to provide the processor with instructions which when executed cause the processor to:
receive input data associated with the audio waveform;
obtain input samples, wherein the input samples are in data compressed format;
select input samples for creating output samples, wherein the output samples are in data compressed format; and
create output data associated with a temporally modified audio waveform using the output samples.
20. A computer program product for temporally modifying an audio waveform, the computer program product being embodied in a tangible computer readable medium and comprising computer instructions, that when executed by a processor and memory, perform the steps, comprising:
receiving input data associated with the audio waveform;
obtaining input samples, wherein the input samples are in data compressed format;
selecting input samples for creating output samples, wherein the output samples are in data compressed format; and
creating output data associated with a temporally modified audio waveform using the output samples.