Time warp activation signal provider, audio signal encoder, method for providing a time warp activation signal, method for encoding an audio signal and computer programs

• US 9,502,049 B2
• Filed: 11/11/2014
• Issued: 11/22/2016
• Est. Priority Date: 07/11/2008
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Bayer, Stefan, Disch, Sascha, Geiger, Ralf, Fuchs, Guillaume, Neuendorf, Max, Schuller, Gerald, Edler, Bernd
• Primary Examiner(s): PULLIAS, JESSE SCOTT
• Application Number:
  US14/538,751
• Publication Number:
  US 20150066489A1
• Time in Patent Office: 742 Days
• Field of Search: 704200-232, 704500-504
• US Class Current: 1/1
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• 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
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 21/04 Time compression or expansion
• CPC Class Codes: G10L 21/043 by changing speed
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

An audio encoder has a window function controller, a windower, a time warper with a final quality check functionality, a time/frequency converter, a TNS stage or a quantizer encoder, the window function controller, the time warper, the TNS stage or an additional noise filling analyzer are controlled by signal analysis results obtained by a time warp analyzer or a signal classifier. Furthermore, a decoder applies a noise filling operation using a manipulated noise filling estimate depending on a harmonic or speech characteristic of the audio signal.

Claims

1. Audio encoder for encoding an audio signal, comprising:

a time warper for warping an audio signal using a variable time warping characteristic;

a time/frequency converter for converting a time warped audio signal into a spectral representation comprising a number of spectral coefficients; and

a processor for processing a variable number of spectral coefficients to generate an encoded audio signal,

wherein the processor is configured for variably setting a number of spectral coefficients for a frame of the audio signal based on the time warping characteristic for the frame so that a bandwidth variation represented by the processed number of frequency coefficients from frame to frame is reduced or eliminated.

2. Audio encoder in accordance with claim 1, further comprising a bandwidth extension encoder for encoding a spectral band above a cross-over frequency using parameters derived from a band of the audio signal above the cross-over frequency, wherein the cross-over frequency is a maximum frequency of a target bandwidth for each frame.

3. Audio encoder in accordance with claim 2, in which the audio signal, before being time warped, is sampled using a normal sampling frequency, and in which the processor is configured to use a predetermined number of spectral coefficients derived from the cross-over frequency and the normal sampling frequency, when the local sampling frequency is equal to the normal sampling frequency, or to use a higher number of spectral coefficients compared to the predetermined number of spectral coefficients, when the local sampling frequency is higher than the normal sampling frequency, or to use a lower number compared to the predetermined number of spectral coefficients, when the local sampling frequency is lower than the normal sampling frequency.

4. Audio encoder in accordance with claim 1,

in which the variable time warping characteristic comprises a local sampling frequency for a frame, and

in which the processor is configured to increase a number of spectral coefficients, when the local sampling frequency is increased, or in which the processor is configured for decreasing the number of spectral coefficients, when the local sampling frequency is decreased.

5. Audio encoder in accordance with claim 4, further comprising a bandwidth extension encoder for encoding a spectral band above a cross-over frequency using parameters derived from a band of the audio signal above the cross-over frequency, wherein the cross-over frequency is a maximum frequency of a target bandwidth for each frame.

6. Audio encoder in accordance with claim 5, in which the audio signal, before being time warped, is sampled using a normal sampling frequency, and in which the processor is configured to use a predetermined number of spectral coefficients derived from the cross-over frequency and the normal sampling frequency, when the local sampling frequency is equal to the normal sampling frequency, or to use a higher number of spectral coefficients compared to the predetermined number of spectral coefficients, when the local sampling frequency is higher than the normal sampling frequency, or to use a lower number compared to the predetermined number of spectral coefficients, when the local sampling frequency is lower than the normal sampling frequency.

7. Audio encoder in accordance with claim 1,

in which the processor comprises a quantizer for quantizing the spectral coefficients to acquire quantized spectral coefficients, and an entropy encoder for entropy encoding the quantized spectral coefficients,

wherein the processor comprises a selector for discarding spectral coefficients not comprised in the set number of spectral coefficients before or after quantizing so that the encoded audio signal only comprises the spectral coefficients, which have not been discarded, or

wherein the processor comprises a selector for adding spectral coefficients needed by the set number of spectral coefficients before or after quantizing so that the encoded audio signal additionally comprises the added spectral coefficients.

8. Method for encoding an audio signal, comprising:

time warping an audio signal using a variable time warping characteristic;

converting a time warped audio signal into a spectral representation comprising a number of spectral coefficients; and

processing a variable number of spectral coefficients to generate an encoded audio signal,

wherein a variable number of spectral coefficients for a frame of the audio signal is set based on the time warping characteristic for the frame so that a bandwidth variation represented by the processed number of frequency coefficients from frame to frame is reduced or eliminated.

9. A non-transitory computer readable medium comprising a computer program including program code for performing, when running on a computer, the method of claim 8.