Enhanced control for compression and decompression of sampled signals

• US 7,791,508 B2
• Filed: 02/25/2009
• Issued: 09/07/2010
• Est. Priority Date: 09/17/2007
• Status: Expired due to Fees

• Current Assignee: Altera Corporation (Intel Corporation)
• Original Assignee: Samplify Systems Incorporated
• Inventors: Wegener, Albert W
• Primary Examiner(s): Nguyen, Khai M
• Application Number:
  US12/392,418
• Publication Number:
  US 20090160685A1
• Time in Patent Office: 559 Days
• Field of Search: 341/61, 341/65, 341/67, 341/155
• US Class Current: 341/61
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

Control of signal compression is coordinated by selectively modifying control parameters affecting the bit rate, sample rate, dynamic range and compression operations. Selected control parameters are modified according to a control function. The control function can include a ratio parameter that indicates the relative or proportional amounts of change to the control parameters. Alternatively, the control function can be represented in a lookup table with values for the selected control parameters related by the control function. Downsampling the input signal samples according to a sample rate control parameter is followed by upsampling to the original sample rate. Errors are calculated between the upsampled and original signal samples. Encoding of the downsampled signal samples and the error samples is performed in accordance with a compression control parameter. The sample rate control parameter and compression control parameter are determined based on the control function.

Claims

1. A method for compressing a sampled input signal having a plurality of signal samples with a dynamic range and a sample rate, comprising:

setting a characteristic of a control function in memory;

applying the control function to determine a sample rate control parameter and a compression control parameter in accordance with the characteristic of the control function;

downsampling the signal samples in accordance with the sample rate control parameter to form downsampled signal samples having a reduced sample rate;

upsampling the downsampled signal samples to form upsampled signal samples having the sample rate, wherein the upsampled signal samples are approximations of corresponding signal samples in the plurality of signal samples;

subtracting the upsampled signal samples from the corresponding signal samples to form error samples;

encoding the downsampled signal samples in accordance with the compression control parameter to form encoded downsampled signal samples; and

encoding the error samples in accordance with the compression control parameter to form encoded error samples, wherein the encoded downsampled signal samples and the encoded error samples form a plurality of compressed samples.

2. The method of claim 1, wherein the step of downsampling applies a downsampling Farrow filter to the signal samples to form the downsampled signal samples and the step of upsampling applies an upsampling Farrow filter to the downsampled signal samples to form the upsampled signal samples.

3. The method of claim 1, wherein the step of downsampling applies a downsampling polyphase filter to the signal samples to form the downsampled signal samples and the step of upsampling applies an upsampling polyphase filter to the downsampled signal samples to form the upsampled signal samples.

4. The method of claim 1, further comprising one of the following steps performed in accordance with a dynamic range control parameter:

adjusting the dynamic range of the downsampled signal samples in accordance with the dynamic range control parameter to form modified signal samples prior to the step of encoding, wherein the encoding is applied to the modified signal samples to form the encoded downsampled signal samples; and

adjusting the dynamic range of the signal samples in accordance with the dynamic range control parameter to form adjusted signal samples prior to the step of downsampling, wherein the downsampling is applied to the adjusted signal samples to form the downsampled signal samples.

5. The method of claim 4, further comprising the step of:

applying the control function to determine the dynamic range control parameter.

6. The method of claim 4, further comprising:

encoding the dynamic range control parameter to form an encoded dynamic range control parameter, wherein the compressed samples include the encoded dynamic range control parameter.

7. The method of claim 1, further comprising:

encoding the sample rate control parameter and the compression control parameter to form encoded control parameters, wherein the compressed samples include the encoded control parameters.

8. The method of claim 1, further comprising:

measuring a characteristic of the compressed samples to form a feedback parameter; and

modifying at least one of the sample rate control parameter and the compression control parameter in accordance with the feedback parameter, wherein the sample rate control parameter and the compression control parameter are modified in accordance with the control function.

9. The method of claim 1, wherein the step of downsampling the signal samples applies non-uniform sampling to form the downsampled signal samples having non-uniform sample intervals, wherein the reduced sample rate is an average sample rate for the downsampled signal samples.

10. The method of claim 1, wherein the step of encoding the downsampled signal samples further comprises:

applying Huffman encoding to the downsampled signal samples to form the encoded downsampled signal samples.

11. The method of claim 1, wherein the step of encoding the downsampled signal samples further comprises:

calculating first or higher order derivatives of the downsampled signal samples to produce derivative samples; and

encoding the derivative samples to form the encoded downsampled signal samples.

12. The method of claim 1, further comprising the following steps prior to the step of downsampling:

reordering the signal samples to form at least one set of demultiplexed signal samples; and

inverting selected samples in each set of demultiplexed signal samples to form a corresponding set of demultiplexed input samples, wherein the step of downsampling is applied to each set of demultiplexed input samples to form a corresponding set of downsampled demultiplexed samples.

13. The method of claim 12, wherein the step of encoding the downsampled signal samples further comprises:

applying Huffman encoding to each set of downsampled demultiplexed samples to form a corresponding set of encoded downsampled signal samples included in the compressed samples.

14. The method of claim 12, wherein the step of encoding the downsampled signal samples further comprises:

calculating first or higher order derivatives of each set of downsampled demultiplexed samples to produce a corresponding set of derivative samples; and

encoding each set of derivative samples to form the encoded downsampled signal samples included in the compressed samples.

15. The method of claim 12, wherein the step of upsampling is applied to each set of downsampled demultiplexed samples to form a corresponding set of upsampled demultiplexed samples, wherein the step of subtracting subtracts each set of upsampled demultiplexed samples from the corresponding set of demultiplexed input samples to form a corresponding set of error samples, wherein the step of encoding the error samples is applied to each set of error samples to form the encoded error samples included in the compressed samples.

16. The method of claim 12, further including at least one of a reordering control parameter and an inversion control parameter, wherein the step of reordering is performed in accordance with the reordering control parameter, wherein the step of inverting is performed in accordance with the inversion control parameter.

17. The method of claim 1, wherein the control function includes a ratio parameter that represents a relationship between a first change value corresponding to the sample rate control parameter and a second change value corresponding to the compression control parameter, wherein the step of setting a characteristic of a control function includes setting a value for the ratio parameter, wherein the step of applying the control function determines the sample rate control parameter and the compression control parameter in accordance with the value of the ratio parameter.

18. The method of claim 1, wherein the step of setting a characteristic of a control function further comprises:

representing the control function with a lookup table in memory, wherein the lookup table includes a first set of parameters corresponding to the sample rate control parameter and a second set of parameters corresponding to the compression control parameter; and

selecting a first parameter from the first set and a second parameter from the second set, wherein the step of applying the control function determines the sample rate control parameter in accordance with the first parameter and the compression control parameter in accordance with the second parameter.

19. The method of claim 1, wherein the sampled input signal is an output of an analog to digital converter.

20. The method of claim 1, further comprising:

transferring the compressed sample to an interface or to storage; and

decompressing the compressed samples received from the interface or storage, the decompressing comprising;

decoding the compressed samples including decoding the encoded downsampled signal samples and decoding the encoded error samples to produce decoded downsampled signal samples and decoded error samples, respectively;

upsampling the decoded downsampled signal samples to form reconstructed upsampled signal samples having the sample rate; and

adding the reconstructed upsampled signal samples to the corresponding decoded error samples to form reconstructed signal samples corresponding to the plurality of signal samples.

21. The method of claim 20, wherein the reconstructed signal samples are provided to an input of a digital to analog converter.

22. An integrated circuit device including one or more integrated circuit chips, comprising

a substrate including one or more integrated circuit chips;

memory on the substrate;

logic on the substrate configured to receive as input a characteristic of a control function and set the characteristic in the memory;

a controller on the substrate coupled to the memory to apply the control function to determine a sample rate control parameter and a compression control parameter in accordance with the characteristic of the control function;

a data channel on the substrate carrying a sampled input signal having a plurality of signal samples with a dynamic range and a sample rate;

a downsampler on the substrate coupled to the data channel to downsample the signal samples to form downsampled signal samples having a reduced sample rate, the downsampler responding to the controller to downsample in accordance with the sample rate control parameter;

an upsampler on the substrate coupled to the downsampler to upsample the downsampled signal samples to form upsampled signal samples having the sample rate, wherein the upsampled signal samples are approximations of corresponding signal samples in the plurality of signal samples;

a delay buffer on the substrate coupled to the data channel to store the signal samples for time alignment with the upsampled signal samples to produce time-aligned signal samples;

a subtractor on the substrate coupled to the delay buffer and coupled to the upsampler for subtracting the upsampled signal samples from the corresponding time-aligned signal samples to form error samples; and

an encoder on the substrate coupled to the downsampler to encode the downsampled signal samples and coupled to the subtractor to encode the error samples, the encoder responding to the controller to encode in accordance with the compression control parameter, wherein the encoder produces encoded downsampled signal samples and encoded error samples to form a plurality of compressed samples.

23. The integrated circuit device of claim 22, wherein the downsampler further comprises a downsampling Farrow filter and the upsampler further comprises an upsampling Farrow filter.

24. The integrated circuit device of claim 22, wherein the downsampler further comprises a downsampling polyphase filter and the upsampler further comprises an upsampling polyphase filter.

25. The integrated circuit device of claim 22, further comprising:

an analog to digital converter on the substrate coupled to the data channel to provide the sampled input signal; and

an analog input channel coupled to the analog to digital converter to provide an input analog signal, wherein the analog to digital converter converts the input analog signal to the sampled input signal.