Hysteretic synchronization system for MPEG audio frame decoder
DC CAFCFirst Claim
1. A system for synchronizing a data processing unit to a bitstream having synchronization codes successively spaced by a predetermined interval with data for processing disposed between the synchronization codes, said bitstream having a data header comprising a bitrate and a sampling frequency, said system comprising:
- a detector for detecting said synchronization codes;
a sensor for sensing intervals between successive synchronization codes;
a comparator for comparing said intervals with said predetermined interval;
a controller for determining both;
(A) whether the system is synchronized to the bitstream after the comparator has detected a first predetermined number of said intervals; and
(B) whether the system is unsynchronized to the bitstream after the comparator has detected a second predetermined number of said intervals; and
a header sensor for sensing said data header and calculating said predetermined interval from said information.
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Abstract
An audio decoder decodes audio frames included in a Motion Picture Experts Group (MPEG) bitstream for presentation or playing. Each audio frame includes a synchronization code and a frame header, followed by audio data. The synchronization codes are detected, and it is determined that the decoder is synchronized to the bitstream after a first predetermined number, for example three, of successive valid audio frames have been detected. It is similarly determined that the decoder is unsynchronized to the bitstream after a second predetermined number, which can also be three, of successive invalid audio frames have been detected. Each and every frame is determined to be valid if its header parameters are valid, it passes the CRC error check (optional), no syntax errors are detected and its frame length (interval) is as expected. The proper frame interval can be determined from the information in the header following each valid synchronization code, or can be determined by counting the number of bits between the first and second valid synchronization codes. The decoder can be muted while out of synchronization to minimize distortion of the audio presentation.
45 Citations
29 Claims
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1. A system for synchronizing a data processing unit to a bitstream having synchronization codes successively spaced by a predetermined interval with data for processing disposed between the synchronization codes, said bitstream having a data header comprising a bitrate and a sampling frequency, said system comprising:
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a detector for detecting said synchronization codes; a sensor for sensing intervals between successive synchronization codes; a comparator for comparing said intervals with said predetermined interval; a controller for determining both; (A) whether the system is synchronized to the bitstream after the comparator has detected a first predetermined number of said intervals; and (B) whether the system is unsynchronized to the bitstream after the comparator has detected a second predetermined number of said intervals; and a header sensor for sensing said data header and calculating said predetermined interval from said information. - View Dependent Claims (2, 3, 4)
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5. A system for synchronizing a data processing unit to a bitstream having successively spaced synchronization codes and data disposed between the synchronization codes, the bitstream further comprising a data header following each synchronization code including information from which intervals between successive synchronization codes can be calculated, the system comprising:
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a detector for detecting said synchronization codes; a sensor for sensing intervals between successive synchronization codes; a comparator for comparing said intervals with synchronization code intervals; a controller for determining if the system is synchronized to the bitstream depending on satisfaction of a first predetermined condition and if the system is unsynchronized to the bitstream depending on satisfaction of a second predetermined condition; and a sensor for sensing said data header and calculating intervals between successive synchronization codes from said information. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for synchronizing a data processing system to a bitstream including synchronization codes successively spaced from each other by a predetermined interval, data disposed between the synchronization codes, and a data header including information from which said predetermined interval can be calculated, comprising the steps of:
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(a) detecting said synchronization codes; (b) sensing intervals between successive synchronization codes; (c) comparing said intervals with said predetermined interval; (d) determining that the system is synchronized to the bitstream based on a first predetermined condition; (e) determining that the system is unsynchronized to the bitstream based on a second predetermined condition; and (f) sensing said data header and calculating said predetermined interval from said information between steps (a) and (c). - View Dependent Claims (17, 18, 19)
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20. A method for synchronizing a data processing system to a bitstream including synchronization codes spaced at a predetermined interval, data disposed between the synchronization codes, and a data header including information from which said predetermined interval can be calculated, comprising the steps of:
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(a) detecting said synchronization codes; (b) sensing intervals between successive synchronization codes; (c) comparing said intervals with said predetermined interval; (d) determining system synchronization and unsynchronization based on predetermined conditions, wherein; (e) sensing said header and calculating said predetermined interval from said information between steps (a) and (c). - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29)
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Specification