Method and apparatus for sample rate pre-and post-processing to achieve maximal coding gain for transform-based audio encoding and decoding

• US 6,384,759 B2
• Filed: 02/02/2001
• Issued: 05/07/2002
• Est. Priority Date: 12/30/1998
• Status: Expired due to Term

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Snyder, James H.
• Primary Examiner(s): Young, Brian
• Assistant Examiner(s): Nguyen, John B
• Application Number:
  US09/773,492
• Publication Number:
  US 20010005173A1
• Time in Patent Office: 459 Days
• Field of Search: 341/123, 341/110, 341/122, 341/144, 341/155, 341/61, 341/143, 704/205, 704/500, 395/2.39, 395/2.14, 348/390
• US Class Current: 341/123
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering

Abstract

The invention relates to a method and apparatus for achieving maximal coding gain for audio transmission. More particularly, at a chosen sample rate and frequency range value, an audio input signal is downsampled to the sample rate, encoded and transmitted at a given bit rate. At the receiving end, the downsampled signal is decoded and upsampled to the original or other suitable sample rate. The upsampled signal is then audibly output. Since resampling ratios using “small” numbers prove to be more computationally efficient, this method and apparatus supports resampling ratios which imply both standard and non-standard sampling ratios in the codec.

Claims

1. A method for preparing audio signals for encoding and transmitting in a multi-media communication network, comprising:

receiving an input audio signal;

downsampling the input audio signal at a first communications device from an original sampling rate to a predetermined intermediate sampling rate, the downsampled signal including a resampling ratio,

resampling the downsampled signal to a predetermined sampling rate , based on the resampling ratio, for subsequent output.

2. The method of claim 1, further comprising:

storing the encoded signal.

3. The method of claim 1, wherein the audio signal is downsampled to a standard sampling rate.

4. The method of claim 1, wherein the audio signal is downsampled to a non-standard sampling rate.

5. The method of claim 1, wherein the audio signal is upsampled to a standard sampling rate.

6. The method of claim 1, wherein the audio signal is upsampled to a non-standard sampling rate.

7. The method of claim 1, further comprising determining the sampling rate and a maximum frequency range algorithmically or according to a table.

8. The method of claim 1, wherein the transmitting includes transmitting at least one of a given bit rate, a frequency range, and a desired distortion level that is predetermined.

9. The method of claim 1, further comprising:

creating a header for the encoded signal that includes a downsampling ratio;

transmitting the header with the encoded signal to the second communications device.

10. The method of claim 1, wherein the input audio signal is downsampled by using computationally efficient integers for downsampling.

11. The method of claim 1, wherein resampling the downsampled audio signal comprises using computationally efficient small integers for resampling.

12. The method of claim 1, wherein the input audio signal is a baseboard input signal.

13. The method of claim 1, wherein the downsampled signal includes side channel information that includes the resampling ratio.

14. The method of claim 1, wherein the downsampled signal has a bit stream that includes at least one data packet that includes the resampling ratio.

15. An apparatus for resampling audio signals and transmitting the audio signals in a multi-media communications network, comprising:

a first terminal including a downsampler that receives an input audio signal and downsamples the input audio signal from an original sampling rate to a predetermined intermediate sampling rate, the downsampled signal including a resampling ratio; and

a second terminal including a resampler that resamples the downsampled signal to a predetermined sampling rate, based on the resampling ratio, for subsequent output.

16. The apparatus of claim 15, further comprising:

a memory for storing the encoded signal.

17. The apparatus of claim 15, wherein the audio signal is downsampled to a standard sampling rate.

18. The apparatus of claim 15, wherein the audio signal is downsampled to a non-standard sampling rate.

19. The apparatus of claim 15, wherein the audio signal is upsampled to a standard sampling rate.

20. The apparatus of claim 15, wherein the audio signal is upsampled to a non-standard sampling rate.

21. The apparatus of claim 15, further comprising a determination device that determines the sampling rate and a maximum frequency range algorithmically or according to a table.

22. The apparatus of claim 15, further comprising a transmitter that transmits the audio signal from the first terminal to the second terminal at a bit rate, in a frequency range, and at a distortion level, at least one of the bit rate, the frequency range, and the distortion level being fixed.

23. The apparatus of claim 15, further comprising an encoder that creates a header for the downsampled signal, and a transmitter that transmits the header with the downsampled signal.

24. The apparatus of claim 15, wherein the downsampler uses computationally efficient small integers for downsampling.

25. The apparatus of claim 15, wherein the resampler uses computationally efficient small integers for resampling.

26. The apparatus of claim 15, wherein the input audio signal is a baseboard input signal.

27. The apparatus of claim 15, wherein the downsampled signal includes side channel information that includes the resampling ratio.

28. The apparatus of claim 15, wherein the downsampled signal includes a bit stream that includes at least one data package that includes the resampling ratio.