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
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.
1. Audio encoder for encoding an audio signal, comprising:
a time warper;
a time-frequency converter for performing a time/frequency conversion of a time-warped audio signal into a spectral representation;
a quantizer for quantizing audio values, wherein the quantizer is configured to quantize to zero audio values below a quantization threshold;
a noise filling calculator for estimating a measure of an energy of audio values quantized to zero for a time frame of the audio signal to acquire a noise filling measure;
an audio signal analyzer for analyzing, whether the time frame of the audio signal comprises a harmonic or speech characteristic;
a manipulator for manipulating the noise filling measure depending on a harmonic or a speech characteristic of the audio signal to acquire a manipulated noise filling measure; and
an output interface for generating an encoded signal for transmission or storage, the encoded signal comprising the manipulated noise filling measure;
wherein the manipulator is configured to apply a normal noise level when the signal does not comprise an harmonic or speech characteristic and when no time warp is applied, and to manipulate the noise filling level to be lower than in the normal case when a pitch contour was found, which indicates a harmonic content, and the time warp is active.
2. The audio encoder in accordance with claim 1 ,
in which the audio signal analyzer comprises a pitch trigger for generating an indication of a pitch, when a pitch is found in the time frame of the audio signal, and
in which the manipulator is configured for reducing the noise filling measure, when a pitch is found.
3. Audio encoder in accordance with claim 1 ,
in which the audio signal analyzer comprises a voiced/unvoiced detector for detecting, whether at least a portion of the time frame is voiced,
in which the manipulator is configured for reducing the noise filling measure or for zeroing the noise filling measure, when the portion is detected to be voiced, and
in which the manipulator is configured to not manipulate or to manipulate the noise filling measure to a smaller degree, when the portion is detected to be unvoiced.
4. Method for encoding an audio signal, comprising:
time warping an audio signal;
performing a time/frequency conversion of a time-warped audio signal into a spectral representation;
quantizing audio values, wherein values below a quantization threshold are quantized to zero;
estimating a measure of an energy of audio values quantized to zero for a time frame of the audio signal;
analyzing, whether the time frame of the audio signal comprises a harmonic or speech characteristic;
manipulating the noise filling measure depending on a harmonic or a speech characteristic of the audio signal to acquire a manipulated noise filling measure such that a normal noise level is applied when the signal does not comprise an harmonic or speech characteristic and when no time warp is applied, and such that the noise filling level is manipulated to be lower than in the normal case when a pitch contour was found, which indicates a harmonic content, and the time warp is active; and
generating an encoded signal for transmission or storage, the encoded signal comprising the manipulated noise filling measure.
5. A non-transitory computer-readable medium having program code stored thereon, wherein the program code, when executed by a computer, performs the method of claim 4 .