System and method of processing compressed audio data
View Patent ↗A system and method of synchronizing to a frame sequence in an input signal includes tolerating data errors within certain error thresholds. In an embodiment, a Hamming distance between data included in a frame alignment word field and an expected value is compared to a predetermined Hamming distance to determine a synchronization event.
1. A method of processing compressed audio data, the method comprising:
receiving a compressed audio data signal communicated in a plurality of frames, each of the plurality of frames having a frame alignment word (FAW) field and a control word;
incrementing a control word counter value when the control word is received; and
determining a synchronization event indicating a synchronization with the plurality of frames of the received compressed audio data signal when each frame of a predetermined number of sequential frames of the plurality of frames that is received has a FAW field that includes data that is within a predetermined Hamming distance from a predetermined expected value and when the control word counter value satisfies a control word counter threshold value, but not when the data exceeds the predetermined Hamming distance from the predetermined expected value.
2. The method of claim 1 , wherein the predetermined Hamming distance is two, and wherein the predetermined number of sequential frames is ten.
3. The method of claim 2 , wherein the tenth frame of the plurality of frames received before determining the synchronization event has a FAW field that includes data that has a Hamming distance of zero from the predetermined expected value.
4. The method of claim 3 , wherein the ninth frame of the plurality of frames received before determining the synchronization event has a FAW field that includes data that has a Hamming distance of one from the predetermined expected value.
5. The method of claim 4 , wherein at least eight sequential frames of the nine frames received prior to determining the synchronization event have a control word that includes data that matches a first data pattern.
6. The method of claim 5 , wherein each frame of the plurality of frames is a NICAM frame, wherein the control word comprises a c 1 bit, a c 3 bit and a c 4 bit, and wherein the first data pattern comprises the data included in the control word corresponding to the c 1 bit, the c 3 bit, and the c 4 bit of the control word of the eighth frame received prior to the determining of the synchronization event.
7. The method of claim 1 , wherein the synchronization event comprises a NICAM sound output.
8. The method of claim 1 , wherein the synchronization event comprises setting a register bit value.
9. The method of claim 1 , wherein a last frame received prior to determining the synchronization event has a payload data field that includes data, and wherein the synchronization event comprises sending the data from the payload data field of the last frame to a descrambler.
10. A non-transitory computer readable memory comprising instructions executable by a processor to implement:
a shift register to receive an input data stream comprising a plurality of frames, each of the plurality of frames having a frame alignment word (FAW) field and a control word;
a counter that is incremented when each control word is detected; and
detection logic coupled to the shift register to synchronize and maintain synchronization to the plurality of frames of the input data stream when a first frame of the plurality of frames that is received has a first FAW field that includes data that matches a predetermined expected FAW and when each frame received after the first frame of the plurality of frames has a FAW field that includes data that does not exactly match the predetermined expected FAW and wherein each frame received after the first frame of the plurality of frames has a FAW field that includes data that is a Hamming distance of not more than two from the predetermined expected FAW and when the counter satisfies a control word threshold.
11. The non-transitory computer readable memory of claim 10 , wherein the detection logic releases synchronization when a predetermined number of sequential frames are received, wherein each of the predetermined number of sequential frames has a control word that includes data that does not match a first data pattern.
12. The non-transitory computer readable memory of claim 11 , wherein each frame of the plurality of frames is a near instantaneous companded audio multiplex (NICAM) frame.
13. The non-transitory computer readable memory of claim 12 , wherein the control word includes a c 1 , c 3 and c 4 bit, and wherein the first data pattern comprises logical values corresponding to the c 1 , c 3 and c 4 bits.
14. A frame sequence detector comprising:
an input to receive an input data stream comprising a plurality of frames, each of the plurality of frames having a control word field and frame alignment word field; and
a processor to determine a synchronization event in response to an error characteristic of the data included in the control word field of a predetermined number of sequentially received frames, and in response to a control word count satisfying a threshold.
15. The detector of claim 14 , wherein the synchronization event indicates synchronizing to the plurality of frames of the input data stream.
16. The detector of claim 15 , wherein the error characteristic comprises at least three bits of the data included in the control word field of each of the predetermined number of sequentially received frames matching an expected value.
17. The detector of claim 16 , wherein the predetermined number of sequentially received frames is eight.
18. The detector of claim 14 , wherein the input data stream comprises digital audio data.
19. The detector of claim 18 , wherein the input data stream is a near instantaneous companded audio multiplex (NICAM) frame sequence.
20. The detector of claim 14 , wherein the synchronization event indicates a loss of synchronization to the plurality of frames.
21. The detector of claim 20 , wherein the error characteristic comprises at least one bit of a predetermined selection of bits of the data included in the control word field of each of the sequentially received frames not matching an expected value.
22. The detector of claim 21 , wherein the predetermined number of sequentially received frames is eight.
23. The detector of claim 22 , wherein the input data stream is a near instantaneous companded audio multiplex (NICAM) frame sequence.
24. The detector of claim 23 , wherein the predetermined selection of bits is the c 1 , c 3 and c 4 bit of the control word field of each NICAM frame.