System and method for processing audio data into a plurality of frequency components
An encoder operable to filter audio signals into a plurality of frequency band components, generate quantized digital components for each band, identify a potential for pre-echo events within the generated quantized digital components, generate an approximate signal by decoding the quantized digital components using inverse pulse code modulation, generate an error signal by comparing the approximate signal with the sampled audio signal, and process the error signal and quantized digital components. The encoder operable to process the error signal by processing delayed audio signals and Q band values, determining the potential for pre-echo events from the Q band values, and determining scale factors and MDCT block sizes for the potential for pre-echo events. The encoder operable to transform the error signal into high resolution frequency components using the MDCT block sizes, quantize the scale factors and frequency components, and encode the quantized lines, block sizes, and quantized scale factors for inclusion in the bitstream.
1. A system having an audio codec, the system comprising:
an input to an audio encoder configured to receive an audio signal;
one or more processors;
a memory storage having instructions stored therein, the instructions executable by the one or more processors to cause the audio encoder to perform operations to:
generate frequency band components corresponding to the audio signal;
generate scale factors to perceptually shape an error signal, the scale factors derived by altering a spectrum of the audio signal and reducing artifacts caused by quantization;
quantize frequency coefficients by use of the generated scale factors applied to the frequency coefficients prior to the quantization or by use of the generated scale factors in computation of error within a vector quantization that performs the quantization;
pack the quantized frequency coefficients into a bitstream to provide an encoded bitstream;
output the encoded bitstream from the audio encoder, the encoded bitstream including components to produce a signal representative of the audio signal; and
an audio decoder that decodes the encoded bitstream without using scale factors such that scale factors are only generated and used by the audio encoder.
2. The system of claim 1 , wherein the operations include a normalization of the generated frequency coefficients in one or more frequency bands and an application of the scale factors to the normalized generated frequency coefficients.
3. The system of claim 1 , wherein quantization of the frequency coefficients by use of the generated scale factors in the computation of error includes:
a use of the scale factors in computation of a signal-to-noise ratio per frequency band, the audio signal having been transformed to a signal spectrum with the signal spectrum divided into a number of frequency bands; and
a maximization of the signal-to-noise ratio in assignment of pulses to frequency coefficients in each frequency band.
4. The system of claim 1 , wherein, with the audio signal having been transformed to a signal spectrum with the signal spectrum divided into a number of frequency bands, generation of the scale factors includes generation of a scale factors per frequency band.
5. The system of claim 1 , wherein generation of the frequency coefficients corresponding to the audio signal includes an application of a window to a block of time samples of the audio signal and a computation of a frequency transform on the block of time samples to generate a spectrum representation of the block.
6. The system of claim 5 , wherein generation of the scale factors includes a computation of a curve.
7. The system of claim 5 , wherein generation of the scale factors includes an encoding of the block.
8. The system of claim 5 , wherein generation of the scale factors includes an identification of a noise artifact.
9. The system of claim 1 wherein generation of the bitstream includes a bitmask.
10. The system of claim 1 , wherein, with the audio signal having been transformed to a signal spectrum with the signal spectrum divided into a number of frequency bands, use of the generated scale factors includes an application of the generated scale factors to all of the frequency bands.
11. The system of claim 1 , wherein a portion of the audio signal is included in the encoded bitstream.
12. A method comprising:
receiving an audio signal at an input to an audio encoder;
generating frequency band components corresponding to the audio signal using a processor;
generating scale factors to perceptually shape an error signal using the processor, the scale factors derived by altering a spectrum of the audio signal and reducing artifacts caused by quantization;
quantizing frequency coefficients using the processor by use of the generated scale factors applied to the frequency coefficients prior to the quantization or by use of the generated scale factors in computation of error within a vector quantization that performs the quantization;
packing the quantized frequency coefficients into a bitstream to provide an encoded bitstream;
outputting the encoded bitstream from the audio encoder, the encoded bitstream including components to produce a signal representative of the audio signal; and
providing the encoded bitstream to an audio decoder that is configured to decode the encoded bitstream without using scale factors such that scale factors are only generated and used by the audio encoder.
13. The method of claim 12 , further comprising normalizing the generated frequency coefficients in one or more frequency bands and applying the scale factors to the normalized generated frequency coefficients.
14. The method of claim 12 wherein quantizing the frequency coefficients by use of the generated scale factors in the computation of error includes:
using the scale factors in computation of a signal-to-noise ratio per frequency band after the audio signal has been transformed to a signal spectrum with the signal spectrum divided into a number of frequency bands; and
maximizing the signal-to-noise ratio in assignment of pulses to frequency coefficients in each frequency band.
15. The method of claim 12 , further comprising transforming the audio signal to a signal spectrum with the signal spectrum divided into a number of frequency bands and generating scale factors for each frequency band.
16. The method of claim 12 , wherein generating the frequency coefficients corresponding to the audio signal includes applying a window to a block of time samples of the audio signal and computing a frequency transform on the block of time samples to generate a spectrum representation of the block.
17. The method of claim 16 , wherein generating the scale factors includes computing a curve.
18. The method of claim 16 , wherein generating the scale factors includes encoding the block.
19. The method of claim 16 , wherein generating the scale factors includes identifying a noise artifact.
20. The method of claim 12 generating the bitstream includes a bitmask.