Method device and system for an efficient noise injection process for low bitrate audio compression

• US 5,692,102 A
• Filed: 10/26/1995
• Issued: 11/25/1997
• Est. Priority Date: 10/26/1995
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Pan, Davis
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Wieland, Susan
• Application Number:
  US08/548,773
• Time in Patent Office: 761 Days
• Field of Search: 395/2.35, 395/2.39, 395/2.92, 381/41-53
• US Class Current: 704/230
• 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

Abstract

The present invention provides a device, method and system of noise injection to maximize compressed audio quality while enabling bitrate scalability. It includes at least one of an encoder and a decoder. The encoder includes a zero detection unit, coupled to receive a frequency domain quantized signal, for determining a control signal that indicates whether noise injection is implemented and a normalization computation unit, coupled to receive at least unquantized signal values and the control signal, for determining a normalization term in accordance with the control signal. The decoder includes a zero detection unit, coupled to receive a frequency domain quantized signal, for determining a control signal that indicates when noise injection is active and a noise generation and normalization unit, coupled to receive a normalization term and the control signal, for generating, normalizing, and injecting a predetermined noise signal where indicated by the control signal.

Claims

1. A system for efficient noise injection for low bitrate audio compression to maximize audio quality, wherein the system includes at least one of A-B;

A) the encoder including a noise substitution and normalization unit comprising;

1) an encoder zero detection unit, coupled to receive a frequency domain quantized signal, for determining a control signal that indicates whether noise injection is implemented in accordance with a predetermined audio compression scheme;

2) a normalization computation unit, coupled to receive at least unquantized subband values and the control signal from the encoder zero detection unit, for determining an energy normalization term based on the unquantized subband values when the control signal indicates all zero values for predefined regions;

B) the decoder including a noise normalization and injection unit comprising;

1) a decoder zero detection unit, coupled to receive a frequency domain quantized signal, for determining, a control signal that indicates implementation of noise injection is implemented in accordance with a predetermined audio compression scheme when values of the frequency domain quantized signal are zero; and

2) a noise generation and normalization unit, coupled to receive the energy normalization term and the control signal from the decoder zero detection unit, for substituting a predetermined noise signal multiplied by the energy normalization term where indicated by the control signal,

wherein the predetermined audio compression scheme comprises one of A-B;

A) coding an individual quantizer step-size for each pre-defined frequency region; and

B) coding a single global step-size for an entire frame of audio data.

3. The device of claim 1 wherein the noise normalization and injection unit in the decoder is utilized subsequent to bitrate scalability module/modules.

4. The device of claim 1 wherein, in the encoder, the input to the normalization computation unit further includes a quantization step size and the unit substitutes the energy normalization term for the quantizer step size value in accordance with the control signal.

5. The device of claim 1 wherein the device is embodied in least one of:

A) an application specific integrated circuit;

B) a field programmable gate array;

C) a microprocessor; and

D) a computer-readable memory;

arranged and configured for efficient noise injection for low bitrate audio compression to maximize audio quality in accordance with the scheme of claim 1.

10. The method of claim 6 wherein the method is a process whose steps are embodied in least one of:

A) an application specific integrated circuit;

B) a field programmable gate array;

C) a microprocessor; and

D) a computer-readable memory;

arranged and configured for efficient noise injection for low bitrate audio compression to maximize audio quality in accordance with the scheme of claim 4.

2. A device for efficient noise injection for low bitrate audio compression to maximize audio quality, comprising:

at least one of an encoder and a decoder;

A) the encoder including a noise computation and normalization unit comprising;

1) an encoder zero detection unit, coupled to receive a frequency domain quantized signal, for determining a control signal that indicates whether noise injection is implemented in accordance with a predetermined audio-compression scheme;

2) a normalization computation unit, coupled to receive at least unquantized subband values and the control signal from the encoder zero detection unit, for determining an energy normalization term based on the unquantized subband values when the control signal indicates all zero values for predefined regions;

B) the decoder including a noise normalization and injection unit comprising;

1) a decoder zero detection unit, coupled to receive a frequency domain quantized signal, for determining, a control signal that indicates implementation of noise injection according to the predetermined audio compression scheme when values of the frequency domain quantized signal are zero; and

2) a noise generation and normalization unit, coupled to receive the energy normalization term and the control signal from the decoder zero detection unit, for substituting a predetermined noise signal multiplied by the energy normalization term when the control signal indicates all zero values for predefined regions,

wherein the predetermined audio compression scheme comprises one of A-B;

A) coding an individual quantizer step-size for each pre-defined frequency region; and

B) coding a single global step-size for an entire frame of audio data.

6. A method for efficient noise injection for low bitrate audio compression to maximize audio quality, comprising the steps of at least one of A-B:

A) in an encoder, including the steps of;

1) determining, by an encoder zero detection unit, a control signal that indicates whether noise injection is implemented in accordance with a predetermined audio compression scheme;

2) determining, by a noise injection unit, an energy normalization term based at least on unquantized subband values when the control signal indicates all zero values for predefined regions;

B) in a decoder, the steps of;

1) determining, by a decoder zero detection unit, a control signal that indicates implementation of noise injection is implemented in accordance with the predetermined audio compression scheme when values of the frequency domain quantized signal are zero; and

2) substituting, by a noise injection unit, a predetermined noise signal multiplied by the energy normalization term where indicated by the control signal,

wherein the predetermined audio compression scheme comprises one of A-B;

A) coding an individual quantizer step-size for each pre-defined frequency region; and

B) coding a single global step-size for an entire frame of audio data.

7. The method of claim 6 wherein noise normalization and injection is implemented in the decoder subsequent to utilizing bitrate scalability module/modules.

8. The method of claim 6 further including, in the encoder, substituting an energy normalization term for a quantizer step size value where indicated by the control signal.

9. The method of claim 6 wherein the energy normalization term is determined in accordance with an equation of a form:

space="preserve" listing-type="equation">Coded representation=K * log.sub.2 (Σ

(x.sup.2 (n)/y.sup.2 (n)) )

where;

n is the index of samples in the frame,

K is a constant,

x² (n) is the original energy of the signal samples that were quantized to zero, and

y² (n) is the energy of the noise to be substituted for samples quantized to zero,

wherein n ranges from 1 to N, with N=a number of frequency coefficients in one frame of frequency domain signal,

and one of a first predetermined audio compression scheme and a second predetermined compression scheme, wherein;

for the first predetermined audio compression scheme, an energy normalization term is calculated for each pre-defined frequency region whose entire contents is quantized to zero, and for each normalization term, n ranges from a lowest index in the region to the highest index in the region; and

for the second predetermined audio compression scheme, an energy normalization term is calculated once for the whole frame, and n consists only of indices from the set whose corresponding frequency coefficients are quantized to zero.