Rate control strategies for speech and music coding

#This invention is related, in general, to the art of coding digital signals, and more particularly, to a method and a system of controlling coding modes of multimode coding systems for coding speech and music signals.

#In current multimedia applications, audio data streams carry both speech and music signals. Even within a signal type, there are distinct categories of signals. For example, during certain types of speech, the audio signal exhibits a highly periodic signal structure. This type of signal is called voiced signal. On the other hand, a speech signal may exhibit a random structure. Such a signal lacks periodic structure, or pitch, and is termed an unvoiced signal. At certain points in a speech signal, the signal may show only continuous background noise or silence. Such a signal is termed a silence signal. In addition to the above types of speech signals, there also exist transition regions in a typical speech signal wherein the signal is changing from one type, such as unvoiced, to another, such as voiced. In such a region, the signal typically demonstrates one or more large signal spikes on top of a background signal.

#Humans have a finite perceptual capability with respect to audio signals, and errors or noise in signals of different types may be perceived more or less strongly depending upon the base signal type. This is true not only for speech signals but also for other audio signal types such as music signals.

#While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:

#FIG. 1 is a schematic diagram illustrating exemplary network-linked hybrid speech/music coding systems wherein embodiments of the invention may be employed;

#FIG. 2 is a simplified block diagram illustrating the functional modules according to an embodiment of the invention;

#The present invention provides a method and a system for use in a multimode coding system receiving a sequence of audio frames for controlling the coding mode of the system for a current audio frame in the sequence according to the characteristics of the current audio frame, the statistical characteristics of the sequence of audio frames, and the status of a bit-stream buffer provided for buffering the encoded bit-streams generated from the audio frames.

#Before describing embodiments of the invention in detail, it will be helpful to note the following concepts and definitions:

#Frame: a frame is a collection of signal samples. The size of a frame is predefined. Without any loss of generality, the invention will be described assuming a frame size of 20 milliseconds. Any other suitable frame size may alternatively be used.