摘要:
Various strategies for rate/quality control and loss resiliency in an audio codec are described. The various strategies can be used in combination or independently. For example, a real-time speech codec uses intra frame coding/decoding, adaptive multi-mode forward error correction [“FEC”], and rate/quality control techniques. Intra frames help a decoder recover quickly from packet losses, while compression efficiency is still emphasized with predicted frames. Various strategies for inserting intra frames and signaling intra/predicted frames are described. With the adaptive multi-mode FEC, an encoder adaptively selects between multiple modes to efficiently and quickly provide a level of FEC that takes into account the bandwidth currently available for FEC. The FEC information itself may be predictively encoded and decoded relative to primary encoded information. Various rate/quality and FEC control strategies allow additional adaptation to available bandwidth and network conditions.
摘要:
Various strategies for rate/quality control and loss resiliency in an audio codec are described. The various strategies can be used in combination or independently. For example, a real-time speech codec uses intra frame coding/decoding, adaptive multi-mode forward error correction [“FEC”], and rate/quality control techniques. Intra frames help a decoder recover quickly from packet losses, while compression efficiency is still emphasized with predicted frames. Various strategies for inserting intra frames and signaling intra/predicted frames are described. With the adaptive multi-mode FEC, an encoder adaptively selects between multiple modes to efficiently and quickly provide a level of FEC that takes into account the bandwidth currently available for FEC. The FEC information itself may be predictively encoded and decoded relative to primary encoded information. Various rate/quality and FEC control strategies allow additional adaptation to available bandwidth and network conditions.
摘要:
A method of compensating for jitter in a packet stream is described. The method comprises placing undecoded frames extracted from packets in the packet stream into a jitter buffer while decoding frames from the jitter buffer and placing the decoded frames into a sample buffer at a rate determined using an average playout delay. The average playout delay is the running average of the playout delay calculated for each packet as each packet becomes available. The playout delay for each packet is the sum of a sample buffer delay and a jitter buffer delay. As each packet is received, the average playout delay is adjusted based on a comparison of the playout delay associated with the received packet to the current average playout delay.
摘要:
This document describes tools capable of enabling and/or adaptively generating comfort noise. The tools may do so by receiving some background noise, analyzing that noise, and generating comfort noise based on the received background noise. In some embodiments, for example, the tools build and continuously adapt a history based on segments of background noise as they are received from the sender. The tools may use this history to generate comfort noise that is pleasing, relatively accurate, and/or dynamically changing responsive to changes in a speaker's background noise.
摘要:
To reduce audio glitch rendering buffer of an audio application is pre-filled with natural sounding audio rather than zeros. For every frame of audio sent for rendering, the rendering buffer is also pre-filled or the signal is stretched in the buffer in anticipation of a glitch. If the glitch does not occur, then the stretched signal is overwritten and the end user does not notice it. If the glitch does occur, then the rendering buffer is already filled with a stretched version of the previous audio and may result in sound that is acceptable. After recovery from the glitch, any new data is smoothly merged into the fake audio that was generated before.
摘要:
A method and system of performing postfiltering in the frequency domain to improve the quality of a speech signal, especially for synthesized speech resulting from codecs of low bit-rate, is provided. The method comprises LPC tilt computation and compensation methods and modules, a formant filter gain computation method and module, and an anti-aliasing method and module. The formant filter gain calculation employs an LPC representation, an all-pole modeling, a non-linear transformation and a phase computation. The LPC used for deriving the postfilter may be transmitted from an encoder or may be estimated from a synthesized or other speech signal in a decoder or receiver. The invention may be implemented in a linked decoder and encoder. A separate LPC evaluation unit that is responsible for processing and or deriving the LPC may be implemented within the invention.
摘要:
To reduce audio glitch rendering buffer of an audio application is pre-filled with natural sounding audio rather than zeros. For every frame of audio sent for rendering, the rendering buffer is also pre-filled or the signal is stretched in the buffer in anticipation of a glitch. If the glitch does not occur, then the stretched signal is overwritten and the end user does not notice it. If the glitch does occur, then the rendering buffer is already filled with a stretched version of the previous audio and may result in sound that is acceptable. After recovery from the glitch, any new data is smoothly merged into the fake audio that was generated before.
摘要:
Detecting at least one of an echo detector and a noise detector based on analysis of audio streams transmitted to and received from each endpoint of a conference. When certain characteristics of the respective audio streams for a given endpoint are classified as significant against certain criteria, a determination is made as to whether that endpoint is a source of echo and/or noise. Subsequent actions are taken to alert users and/or prevent broadcast of impaired signals.
摘要:
Detecting at least one of an echo detector and a noise detector based on analysis of audio streams transmitted to and received from each endpoint of a conference. When certain characteristics of the respective audio streams for a given endpoint are classified as significant against certain criteria, a determination is made as to whether that endpoint is a source of echo and/or noise. Subsequent actions are taken to alert users and/or prevent broadcast of impaired signals.
摘要:
A method and system of performing postfiltering in the frequency domain to improve the quality of a speech signal, especially for synthesized speech resulting from codecs of low bit-rate, is provided. The method comprises LPC tilt computation and compensation methods and modules, a formant filter gain computation method and module, and an anti-aliasing method and module. The formant filter gain calculation employs an LPC representation, an all-pole modeling, a non-linear transformation and a phase computation. The LPC used for deriving the postfilter may be transmitted from an encoder or may be estimated from a synthesized or other speech signal in a decoder or receiver. The invention may be implemented in a linked decoder and encoder. A separate LPC evaluation unit that is responsible for processing and or deriving the LPC may be implemented within the invention.