Method and System for Frequency Domain Postfiltering of Encoded Audio Data in a Decoder

• US 20110125507A1
• Filed: 07/14/2009
• Published: 05/26/2011
• Est. Priority Date: 07/18/2008
• Status: Abandoned Application

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Yu, Rongshan
• Application Number:
  US13/054,518
• Publication Number:
  US 20110125507A1
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

A decoder configured to generate decoded audio data (e.g., decoded speech data) and including a postfilter coupled and configured to filter encoded audio data in the frequency domain, methods for frequency domain postfiltering of encoded audio data in a decoder, and methods for decoding encoded audio data in a decoder including by postfiltering encoded audio data in the frequency domain in the decoder. In some embodiments, the decoder is configured to decode input encoded audio without performing any time-to-frequency domain transform on encoded audio data to prepare data for postfiltering. Typically, the postfiltering improves the quality of the decoded audio signal by attenuating spectral valley regions thereof to remove excess quantization noise present in the encoded input audio while preserving formants of the decoded audio signal to avoid introducing unnecessary distortion.

Claims

1. A decoder configured to generate decoded audio data in response to input audio indicative of encoded input audio data, said decoder including:

a postfilter coupled and configured to filter encoded audio data in the frequency domain, wherein the decoder is configured to decode the encoded input audio data without performing any time-to-frequency domain transform on encoded audio data to prepare data for filtering in the postfilter.

2. The decoder of claim 1, wherein the postfilter is a frequency domain adaptive postfilter.

3. The decoder of claim 1, also including:

a first subsystem coupled to receive the input audio and configured to generate partially decoded audio data in response to the input audio, and wherein the postfilter is coupled and configured to filter the partially decoded audio data in the frequency domain.

4. The decoder of claim 1, wherein the input audio is indicative of the encoded input audio data and quantization noise, the decoded audio data are indicative of a decoded audio signal, and the postfilter is configured to filter the encoded audio data so as to improve quality of the decoded audio signal by attenuating spectral valley regions thereof to remove at least some of the quantization noise while preserving formants of the decoded audio signal.

5. The decoder of claim 1, wherein the encoded input audio data include LPC residual data, and the postfilter is coupled and configured to receive the LPC residual data and to filter the LPC residual data in the frequency domain.

6. The decoder of claim 1, wherein the encoded input audio data include quantized LPC residual data, and wherein said decoder also includes a subsystem including a dequantizer, the subsystem is configured to generate dequantized LPC residual data in response to the input audio, and the postfilter is coupled to the subsystem and configured to receive the dequantized LPC residual data and to filter said dequantized LPC residual data in the frequency domain.

7. The decoder of claim 1, wherein the encoded input audio data include quantized LPC residual data, and the decoder also includes:

a first subsystem configured to extract the quantized LPC residual data from the input audio,

and wherein the postfilter is a combined dequantizing and postfiltering subsystem of the decoder, coupled and configured to generate dequantized, postfiltered LPC residual data in response to the quantized LPC residual data including by filtering said quantized LPC residual data in the frequency domain.

8. The decoder of claim 1, wherein the postfilter has a transfer function G·

H(e<sup>j{acute over (ω

)}</sup>), where ω

is the frequency, and where;

9. The decoder of claim 8, wherein the gain filter G is:

G(e<sup>j{acute over (ω

)}</sup>)=G=[1/∫

₀^π

|H(e^jω

)|dω

]^1/2.

10. The decoder of claim 8, also including a subsystem configured to generate a dequantized, transformed LPC residual in response to the input audio, and wherein the postfilter is coupled to the subsystem and configured to multiply each data value associated with the frequency ω

of the dequantized, transformed LPC residual by the value |G·

H(e<sup>j{acute over (ω

)}</sup>)|.

11. A decoder configured to generate decoded audio data in response to input audio indicative of encoded input audio data generated in a transform predictive coder having a native frequency domain, said decoder including:

a postfilter coupled and configured to filter encoded audio data in the native frequency domain of the transform predictive coder.

12. The decoder of claim 11, wherein the postfilter is a frequency domain adaptive postfilter.

13. The decoder of claim 11, also including:

a first subsystem coupled to receive the input audio and configured to generate partially decoded audio data in response to the input audio, and wherein the postfilter is coupled and configured to filter the partially decoded audio data in the native frequency domain of the transform predictive coder.

14. The decoder of claim 11, wherein the input audio is indicative of the encoded input audio data and quantization noise, the decoded audio data are indicative of a decoded audio signal, and the postfilter is configured to filter the encoded audio data so as to improve quality of the decoded audio signal by attenuating spectral valley regions thereof to remove at least some of the quantization noise while preserving formants of the decoded audio signal.

15. The decoder of claim 11, wherein the encoded input audio data include LPC residual data, and the postfilter is coupled and configured to receive the LPC residual data and to filter the LPC residual data in the frequency domain.

16. The decoder of claim 11, wherein the encoded input audio data include quantized LPC residual data, and wherein said decoder also includes a subsystem including a dequantizer, the subsystem is configured to generate dequantized LPC residual data in response to the input audio, and the postfilter is coupled to the subsystem and configured to receive the dequantized LPC residual data and to filter said dequantized LPC residual data in the frequency domain.

17. The decoder of claim 11, wherein the encoded input audio data include quantized LPC residual data, and the decoder also includes:

a first subsystem configured to extract the quantized LPC residual data from the input audio,

and wherein the postfilter is a combined dequantizing and postfiltering subsystem of the decoder, coupled and configured to generate dequantized, postfiltered LPC residual data in response to the quantized LPC residual data including by filtering said quantized LPC residual data in the frequency domain.

18. The decoder of claim 11, wherein the postfilter has a transfer function G·

H(e<sup>j{acute over (ω

)}</sup>), where ω

is the frequency, and where;

19. The decoder of claim 18, wherein the gain filter G is:

G(e<sup>j{acute over (ω

)}</sup>)=G=[1/∫

₀^π

|H(e^jω

)²dω

]^1/2.

20. The decoder of claim 18, also including a subsystem configured to generate a dequantized, transformed LPC residual in response to the input audio, and wherein the postfilter is coupled to the subsystem and configured to multiply each data value associated with the frequency ω

of the dequantized, transformed LPC residual by the value |G·

H(e<sup>j{acute over (ω

)}</sup>)|.