Leland Stanford Junior University

Liquid Audio, Inc.

Scott Nathan Levine

Tony S Verma

An audio encoding system includes quantization, phase matching, compressed domain processing and other improvements enabling high fidelity, low bit rate encoding systems to be formed. In a preferred embodiment a novel transient detector is used to divide an audio source into transient, low frequency non-transient and high frequency non-transient regions. Low frequency non-transients are sinusoid modeled and the residual is low frequency noise modeled. Transients are transform coded and high frequency non-transients and transform coded residual is high frequency noise modeled. The preferred embodiment also includes novel sinusoid, transform coded and noise quantization, among other methods for providing high fidelity data reduction and for interfacing sinusoid modeling and transform coding. Compressed domain time compression and expansion are further achieved with no detrimental effect on transients.

Audio encoding apparatus and methods

An audio signal analyzer and encoder is based on a model that considers audio signals to be composed of deterministic or sinusoidal components, transient components representing the onset of notes or other events in an audio signal, and stochastic components. Deterministic components are represented as a series of overlapping sinusoidal waveforms. To generate the deterministic components, the input signal is divided into a set of frequency bands by a multi-complementary filter bank. The frequency band signals are oversampled so as to suppress cross-band aliasing energy in each band. Each frequency band is analyzed and encoded as a set of spectral components using a windowing time frame whose length is inversely proportional to the frequency range in that band. Low frequency bands are encoded using longer time frames than higher frequency bands. Transient components are represented by parameters denoting sinusoidal shaped waveforms produced when the transient components are transformed into a real valued frequency domain waveform. Stochastic or noise components are represented as a series of spectral envelopes. The parameters representing the three signal components compose a stream of compressed encoded audio data that can be further compressed so as to meet a specified transmission bandwidth limit by the deleting the least significant bits of quantized parameter values, reducing the update rates of parameters, and/or deleting the parameters used to encode higher frequency bands until the bandwidth of the compressed audio data meets the bandwidth requirement. Signal quality degrades in a graduated manner with successive reductions in the transmitted data rate.

System and method for multiresolution scalable audio signal encoding

An audio effects processing system and method performs audio effects processing on a subband-by-subband basis using less memory and computational resources than audio effects produced through post processing of a fullband audio signal. The input fullband audio signal is split into subbands and the compressed subbands may be stored in memory of the system as compressed audio subband data or may be generated by real time processing of a fullband audio signal. The system stores in memory a set of prototype subband effects filters, the set including echo, flange, chorus, and reverberation effects filters. A subband filter customization procedure allows a sound system designer to build customized versions of the prototype subband effects filters. One or more of the customized subband effects filters are applied to one or more of the subbands comprising the compressed audio subband data. The compressed audio subband data is then processed through a synthesis filter bank which decompresses and decodes the compressed audio subband data to produce a decompressed decoded audio output signal with the audio effects incorporated in it. The system uses less memory and computational resources by applying the customized subband effects filters to less than a full set of subbands comprising the compressed audio subband data without suffering any psychoacoustical loss. Each subband is processed separately and independent of the other subbands. By computing effects separately for each subband, different effects can be performed on different frequency regions. This allows different effects to be placed on the subbands, providing the ability to create a multiband audio effects processor.

Growing community of inventors

Palo Alto, CA, United States of America

Scott Nathan Levine