Interoperable vocoder
AssigneeDigital Voice Systems, Inc.
InventorJohn C. Hardwick
Life of this patent
Estimating the term…
Abstract
Encoding a sequence of digital speech samples into a bit stream includes dividing the digital speech samples into one or more frames and computing a set of model parameters for the frames. The set of model parameters includes at least a first parameter conveying pitch information. The voicing state of a frame is determined and the first parameter conveying pitch information is modified to designate the determined voicing state of the frame, if the determined voicing state of the frame is equal to one of a set of reserved voicing states. The model parameters are quantized to generate quantizer bits which are used to produce the bit stream.
Claims35
A speech coder configured to encode a sequence of digital speech samples into a bit stream, the speech coder being operable to:
- divide the digital speech samples into one or more frames;
- compute model parameters for multiple frames, the model parameters including at least a first parameter conveying pitch information;
- determine the voicing state of a frame;
- modify the first parameter conveying pitch information to designate the determined voicing state of the frame if the determined voicing state of the frame is equal to one of a set of reserved voicing states;
- and
- quantize the model parameters to generate quantizer bits which are used to produce the bit stream.
A speech coder configured to encode a sequence of digital speech samples into a bit stream, the speech coder being operable to:
- divide the digital speech samples into one or more frames;
- determine whether the digital speech samples for a frame correspond to a tone signal;
- and
- compute model parameters for multiple frames, the model parameters including at least a first parameter representing the pitch and spectral parameters representing the spectral magnitude at harmonic multiples of the pitch;
- if the digital speech samples for a frame are determined to correspond to a tone signal, assign values to the pitch parameter and the spectral parameters to approximate the detected tone signal;
- and
- quantize the model parameters, including the pitch parameter and the spectral parameters to which values are assigned to approximate the detected tone signal if the digital speech samples for the frame are determined to correspond to the tone signal, to generate quantizer bits which are used to produce the bit stream.
The speech coder of claim 21 wherein the produced bit stream is interoperable with the standard vocoder used for APCO Project 25.
A speech decoder configured to decode digital speech samples from a sequence of bits, the speech decoder being operable to:
- divide the sequence of bits into individual frames, each frame containing multiple bits;
- form quantizer values from a frame of bits, the formed quantizer values including at least a first quantizer value representing the pitch and a second quantizer value representing the voicing state;
- determine if the first and second quantizer values belong to a set of multiple reserved quantizer values;
- reconstruct speech model parameters for a frame from the quantizer values, the speech model parameters representing the voicing state of the frame being reconstructed from the first quantizer value representing the pitch if the first and second quantizer values are determined to belong to the set of reserved quantizer values;
- and
- compute a set of digital speech samples from the reconstructed speech model parameters.
A speech decoder configured to decode digital speech samples from a sequence of bits, the speech decoder being operable to:
- divide the sequence of bits into individual frames that each contain multiple bits;
- reconstruct speech model parameters from a frame of bits, the reconstructed speech model parameters for a frame including one or more spectral parameters representing the spectral magnitude information for the frame;
- determine from the reconstructed speech model parameters whether the frame represents a tone signal;
- modify the spectral parameters if the frame represents a tone signal, such that the modified spectral parameters better represent the spectral magnitude information of the determined tone signal;
- and
- generate digital speech samples from the reconstructed speech model parameters and the modified spectral parameters.
Dependencies are inferred from the claim text.