Codec conditioning system and method

• US 20070239295A1
• Filed: 02/23/2007
• Published: 10/11/2007
• Est. Priority Date: 02/24/2006
• Status: Abandoned Application

• Current Assignee: DTS, Inc. (Xperi Inc.)
• Original Assignee: DTS, Inc. (Xperi Inc.)
• Inventors: Thompson, Jeffrey, Reams, Robert, Warner, Aaron
• Application Number:
  US11/710,070
• Publication Number:
  US 20070239295A1
• Time in Patent Office: Days
• US Class Current: 700/94
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding

Abstract

An audio processing application is provided which utilizes an audio codec encode/decode simulation system and a psychoacoustic model to estimate audible quantization noise that may occur during lossy audio compression. Mask-to-noise ratio values are computed for a plurality of frequency bands and are used to intelligently process an audio signal specifically for a given audio codec. In one exemplary embodiment, the mask-to-noise ratio values are used to reduce the extent of perceived artifacts for lossy compression, such as by modifying the energy and/or coherence of frequency bands in which quantization noise is estimated to exceed the masking threshold.

Claims

1. A system for audio signal processing, comprising:

a reference audio codec simulation system receiving a source audio signal and simulating a coding and decoding system to generate a coded audio signal potentially including one or more coding artifacts;

a delay system delaying the source signal; and

a conditioning system receiving the source signal and the coded signal and generating a conditioned output signal that reduces the one or more coding artifacts when the conditioned output signal is subsequently coded and decoded.

2. The system of claim 1 wherein the conditioning system comprises a time domain to frequency domain conversion system.

3. The system of claim 1 wherein the conditioning system comprises an auditory model that generates a spectral masking curve.

4. The system of claim 3 wherein the spectral masking curve includes one or more frequency bands.

5. The system of claim 4 wherein the one or more frequency bands are comprised of one or more Barks.

6. The system of claim 1 wherein the conditioning system comprises a subtractor generating a noise spectrum.

7. The system of claim 1 wherein the conditioning system comprises a threshold system comparing the signal to a mask-to-noise ratio and attenuating the signal where quantization noise exceeds masking criteria.

8. The system of claim 1 wherein the conditioning system comprises a threshold system comparing one or more frequency bands of the signal to one or more frequency bands of a mask-to-noise ratio and attenuating the signal in frequency bands where quantization noise exceeds masking criteria.

9. The system of claim 1 wherein the conditioning system comprises a multiplier that multiplies the signal by a mask-to-noise ratio to attenuate the signal by an amount that a noise component of the reference signal exceeds a masking criteria.

10. The system of claim 1 wherein the conditioning system comprises conditioning means for receiving the reference signal and the delayed signal and generating a conditioned output signal that excludes the one or more coding artifacts when the conditioned output signal is coded and decoded.

11. A system for signal coding, comprising:

a reference codec system receiving a signal and generating a reference signal simulating a coded and decoded signal including one or more coding artifacts;

a delay system delaying the signal; and

a conditioning system receiving the reference signal and the delayed signal and generating a conditioned output signal that excludes the one or more coding artifacts when the conditioned output signal is coded and decoded, the conditioning system further comprising;

a time domain to frequency domain conversion system converting the reference signal and the delayed signal from a time domain to a frequency domain;

a perceptual model that generates a spectral masking curve of the delayed signal;

a subtractor generating a noise spectrum from the frequency domain reference signal and the frequency domain delayed signal;

a divider dividing the spectral masking curve with the noise spectrum to generate a mask-to-noise ratio; and

a threshold system comparing the frequency domain delayed signal to the mask-to-noise ratio and attenuating the frequency domain delayed signal where quantization noise exceeds the mask-to-noise ratio.

12. A method for signal coding, comprising:

receiving a signal and generating a reference signal simulating a coded and decoded signal that includes one or more coding artifacts;

delaying the signal; and

generating a conditioned output signal using the reference signal and the delayed signal that excludes the one or more coding artifacts when the conditioned output signal is coded and decoded.

13. The method of claim 12 wherein generating the conditioned output signal comprises performing a time domain to frequency domain conversion of the delayed signal and the reference signal.

14. The method of claim 12 wherein generating the conditioned output signal comprises processing the delayed signal using a perceptual model that generates a spectral masking curve.

15. The method of claim 12 wherein generating the conditioned output signal comprises generating a noise spectrum using the delayed signal and the reference signal.

16. The method of claim 12 wherein generating the conditioned output signal comprises comparing the delayed signal to a mask-to-noise ratio and attenuating the delayed signal where quantization noise exceeds masking criteria.

17. The method of claim 12 wherein generating the conditioned output signal comprises comparing one or more frequency bands of the delayed signal to one or more frequency bands of a mask-to-noise ratio and attenuating the delayed signal in frequency bands where quantization noise exceeds masking criteria.

18. The method of claim 12 wherein generating the conditioned output signal comprises multiplying the delayed signal by a mask-to-noise ratio to attenuate the delayed signal by an amount that a noise component of the reference signal exceeds a masking criteria.

19. The method of claim 12 wherein generating the conditioned output signal comprises a conditioning step for receiving the reference signal and the delayed signal and generating a conditioned output signal that excludes the one or more coding artifacts when the conditioned output signal is coded and decoded.