Apparatus and Methods for Encoding Digital Audio Data with a Reduced Bit Rate

• US 20070276661A1
• Filed: 04/24/2007
• Published: 11/29/2007
• Est. Priority Date: 04/24/2006
• Status: Active Grant

• Current Assignee: Nero AG
• Original Assignee: Nero AG
• Inventors: Dimkovic, Ivan, Pascutto, Gian
• Granted Patent: US 7,647,222 B2
• Time in Patent Office: Days
• US Class Current: 704/229
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components

Abstract

A method and an apparatus for encoding digital audio data with reduced bit rates, the apparatus having a provider of psycho-acoustically quantized digital audio data with a bit rate being higher than the reduced bit rate. The apparatus further has an identifier for identifying a frequency band according to a selection criterion, the selection criterion being such that an impact on the quality of the digital audio data when the data in the identified frequency band is replaced by generated noise is smaller than the impact on the quality of the digital audio data, which would arise when the data in a different frequency band is replaced by generated noise. The apparatus further has a replacer for replacing data in the identified frequency band of the digital audio data by a noise synthesis parameter.

Claims

1. An apparatus for encoding digital audio data with a reduced bit rate, comprising:

a provider of psycho-acoustically quantized digital audio data with a bit rate being higher than the reduced bit rate;

an identifier for identifying the frequency band according to a selection criterion, the selection criterion being such that an impact on the quality of the digital audio data when the data in the identified frequency band is replaced by generated noise is smaller than the impact on the quality of the digital audio data, which would arise when data in a different frequency band is replaced by generated noise, and

a replacer for replacing data in the identified frequency band of the digital audio data by a noise synthesis parameter, the noise synthesis parameter requiring a smaller amount of data than the data in the identified frequency band, the digital audio data comprising the reduced bit rate.

2. The apparatus of claim 1, wherein the provider is adapted for providing psycho-acoustically quantized digital audio data per frequency band, the frequency band being determined by a filter in a filter bank.

3. The apparatus of claim 1, further comprising an entropy encoder for encoding the digital audio data comprising the reduced bit rate.

4. The apparatus of claim 1, wherein the psycho-acoustically encoded digital data includes entropy encoded quantized spectral data and wherein the provider includes an entropy decoder for entropy decoding the psycho-acoustically encoded digital audio data for providing the psycho-acoustically quantized spectral data and wherein the identifier and the replacer are operative to process the entropy decoded psycho-acoustically quantized digital audio data.

5. The apparatus of claim 1, wherein the provider includes a noise substitution process for replacing spectral data in a pre-selected frequency band by an inserted parameter of the noise substitution process, the pre-selected frequency bands being identified by a pre-selection criterion, the noise substitution process being carried out instead psycho-acoustically quantizing the digital audio data.

6. The apparatus of claim 5, wherein the provider includes a pre-analyzer for analyzing digital audio data according to the pre-selection criterion for pre-selecting the frequency band for insertion of a noise substitution parameter.

7. The apparatus of claim 1, wherein the identifier includes a post-analyzer for analyzing psycho-acoustically quantized data in a frequency band according to the selection criterion for identifying the frequency band for psycho-acoustically quantized data replacements.

8. The apparatus of claim 5, wherein the pre-analyzer or the post-analyzer are operative to utilize the pre-selection criterion or the selection criterion, the pre-selection criterion being different from the selection criterion, the pre-selected frequency band being different from the identified frequency bands.

9. The apparatus of claim 8, wherein the pre-analyzer utilizes the pre-selection criterion and the post-analyzer utilizes the selection criterion corresponding to one of or a combination of the group of a lowest tonality, a lowest or highest signal-to-noise ratio, a lowest or highest signal-to-mask ratio, a lowest energy, a highest central frequency, a best stability in the time domain or a lowest variability in the time domain.

10. The apparatus of claim 1, further comprising a sequence controller for controlling the identifier and the replacer, the sequence controller comparing the reduced bit rate with a target bit rate, adapting the selection criterion such that more frequency bands are identified for replacement by noise synthesis parameters when the reduced bit rate is higher than the target bit rate.

11. The apparatus of claim 1, wherein the replacer is adapted for replacing data of a plurality of frequency bands and for replacing data of consecutive frequency bands by a noise synthesis parameter.

12. The apparatus of claim 1, wherein the provider is operative to provide psycho-acoustically quantized data from encoded digital audio data, the encoded digital audio data being encoded according to ISO/IEC 14496.

13. The apparatus of claim 3, being adapted for encoding digital audio data with reduced bit rate according to ISO/IEC 14496.

14. A method for encoding digital audio data with a reduced bit rate, comprising the steps of:

providing psycho-acoustically quantized digital audio data with a bit rate being higher than the reduced bit rate;

identifying the frequency band according to a selection criterion, the selection criterion being such that an impact on a quality of the digital audio data when the data in the identified band replaced by generated noise is smaller than the impact on the quality of the digital audio data, which would arise when data in a different frequency band is replaced by generated noise, and

replacing data in the identified frequency band of the digital audio data with noise synthesis parameter, the noise synthesis parameter requiring a smaller amount of data than the data in the identified frequency band, the digital audio data comprising the reduced bit rate.

15. A computer program comprising program codes for performing a method for encoding digital audio data with a reduced bit rate, comprising the steps of:

providing psycho-acoustically quantized digital audio data with a bit rate being higher than the reduced bit rate;

identifying the frequency band according to a selection criterion, the selection criterion being such that an impact on a quality of the digital audio data when the data in the identified band replaced by generated noise is smaller than the impact on the quality of the digital audio data, which would arise when data in a different frequency band is replaced by generated noise, and replacing data in the identified frequency band of the digital audio data with noise synthesis parameter, the noise synthesis parameter requiring a smaller amount of data than the data in the identified frequency band, the digital audio data comprising the reduced bit rate, when the program code runs in a computer.