Data processing: speech signal processing – linguistics – language – Speech signal processing – Psychoacoustic
Reexamination Certificate
1998-12-24
2001-05-29
Dorvil, Richemond (Department: 2741)
Data processing: speech signal processing, linguistics, language
Speech signal processing
Psychoacoustic
C704S229000, C704S500000
Reexamination Certificate
active
06240379
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to signal processing systems, and relates more particularly to a system and method for preventing artifacts in an audio data encoder device.
2. Description of the Background Art
Implementing an effective and efficient method of encoding audio data is often a significant consideration for designers, manufacturers, and users of contemporary electronic systems. The evolution of modern digital audio technology has necessitated corresponding improvements in sophisticated, high-performance audio encoding methodologies. For example, the advent of recordable audio compact-disc devices typically requires an encoder-decoder (codec) system to receive and encode source audio data into a format (such as MPEG) that may then be recorded onto appropriate media using the compact-disc device.
Many portions of the audio encoding process are subject to strict technological standards that do not permit system designers to vary the data formats or encoding techniques. Other segments of the audio encoding process may not be altered because the encoded audio data must conform to certain specifications so that a standardized decoder device is able to successfully decode the encoded audio data. These foregoing constraints create substantial limitations for system designers that wish to improve the performance of an audio encoder device.
A paramount goal of most audio encoding systems is to encode the source audio data into an appropriate and advantageous format without introducing any sound artifacts generated by the audio encoding process. In other words, an audio decoder must be able to decode the encoded audio data for transparent reproduction by an audio playback system without introducing any sound artifacts created by the encoding and decoding processes.
Digital audio encoders typically process and compress sequential units of audio data called “frames”. A particularly objectionable sound artifact called a “discontinuity” may be created when successive frames of audio data are encoded with non-uniform amplitude or frequency components. The discontinuities become readily apparent to the human ear whenever the encoded audio data is decoded and reproduced by an audio playback system.
Furthermore, to effectively encode audio data, the audio encoder must allocate a finite number of binary digits (bits) to the frequency components of the audio data, so that the encoding process achieves optimal representation of the source audio data. An efficient bit allocation technique that prevents discontinuity artifacts would thus provide significant advantages to an audio decoder device. Therefore, for all the foregoing reasons, an improved system and method are needed for preventing artifacts in an audio data encoder device.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are disclosed for preventing artifacts in an audio data encoder device. In one embodiment of the present invention, an encoder filter bank initially divides frames of received source audio data into frequency sub-bands. In the preferred embodiment, the filter bank preferably generates thirty-two discrete sub-bands per frame, and then provides the sub-bands to a bit allocator.
A psycho-acoustic modeler also receives the source audio data to responsively determine signal-to-masking ratios (SMRs), and then provide the SMRs to the bit allocator. Next, the bit allocator identifies the initial frame of sub-bands received from the filter bank, and then allocates a finite number of available allocation bits to selected sub-bands of the initial frame using a bit allocation process. The bit allocator then advances to a new current frame by moving forward one frame to arrive at the next frame of sub-bands provided from the filter bank.
Next, the bit allocator checks the new current frame for the presence of a significant event. In the preferred embodiment, the bit allocator detects a significant event whenever the difference in signal-to-masking ratios of successive frames (the current frame and the immediately preceding frame) exceeds a selectable threshold value. Other criteria for determining a significant event are likewise contemplated for use with the present invention
If the bit allocator detects a significant event in the current frame, then the bit allocator performs the bit allocation process referred to above. However, if the bit allocator does not detect a significant event in the current frame, then, the bit allocator performs a prebit allocation procedure to form an initial sub-band set for the current frame. In one embodiment, the bit allocator preferably preallocates one bit per sample (from the available allocation bits) to each sub-band that was allocated bits in the immediately preceding frame to form the initial sub-band set for the current frame.
Then, the bit allocator performs the foregoing bit allocation process by allocating one bit per sample from the available allocation bits to the sub-band (from the initial sub-band set) with the highest SMR. Next, the bit allocator subtracts six decibels from the sub-band with the highest SMR that was just allocated the single bit. The bit allocator then determines whether any available allocation bits remain.
If available allocation bits remain, then the bit allocator continues to perform the bit allocation process for the current frame. However, if no available allocation bits remain, then the bit allocator determines whether any unprocessed frames of filtered audio data remain. If frames of filtered audio data remain unprocessed, then the bit allocator returns to process another frame of filtered audio data. However, if no frames of audio data remain, then the bit allocator has completed allocating bits to the audio data, and the foregoing bit allocation process terminates. The present invention thus efficiently and effectively perform a sub-band forcing strategy to implement a system and method for preventing artifacts in an audio data encoder device.
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Dorvil Richemond
Koerner Gregory J.
Simon & Koerner LLP
Sony Corporation
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