System and method of audio detection
View Patent ↗A system and method for detecting a mode of an audio signal is disclosed. The system includes an integrated circuit with an input to receive a signal and an audio processor coupled to the input. The audio processor includes an audio standard detection module, wherein the audio standard detection module detects a characteristic of the received signal that identifies a television audio standard by measuring the energy level of a plurality of different frequency bands of the received signal.
1. An integrated circuit, comprising:
an input to receive a signal; and
an audio processor coupled to the input, the audio processor including an audio standard detection module to detect in less than 13 milliseconds a characteristic of the received signal that identifies a television audio standard by measuring an energy level of a plurality of different frequency bands of the received signal.
2. The integrated circuit of claim 1 , wherein the audio standard detection module has a first mode of operation and a second mode of operation, wherein in the first mode of operation the audio standard detection module is operable to detect the television audio standard, and in the second mode of operation the audio standard detection module is operable to demodulate the received signal.
3. The integrated circuit of claim 2 , wherein in the second mode of operation, the audio processor is configured base on frequency parameters of the the detected television audio standard.
4. The integrated circuit of claim 2 wherein the audio processor includes a channel filter to perform noise reduction of the received signal.
5. The integrated circuit of claim 2 , wherein the television audio standard includes at least one of a Broadcast Television Systems Committee (BTSC) standard, an Electronic Industries Alliance/J (EIA/J) standard, a Near Instantaneous Companded Audio Multiplex L (NICAM L) standard, a NICAM D/K standard, a NICAM I standard, a NICAM B/G, M standard, an A2 D/K (Type 1) standard, an A2 D/K (Type 2) standard, an A2 D/K (Type 3) standard, an A2 B/G standard.
6. The integrated circuit of claim 2 , wherein a frequency of the signal is between 4 and 7 Megahertz.
7. An audio standard detection module, comprising:
an input to receive an audio signal;
a first mixer coupled to the input to frequency shift the audio signal based on a first selected reference frequency to output a first frequency shifted audio signal;
an energy measurement module responsive to the first mixer to measure a first energy level of the frequency shifted audio signal, the energy measurement module including logic to determine an absolute value based on the output of the first mixer; and
decision logic to determine an audio standard for the audio signal based on an output of the energy measurement module.
8. The audio standard detection module of claim 7 , wherein the energy measurement module includes an integrator.
9. The audio standard detection module of claim 7 , wherein the energy measurement module includes a Cascaded Integrator-Comb (CIC) decimator.
10. The audio standard detection module of claim 7 , wherein the energy measurement module includes a channel filter.
11. The audio standard detection module of claim 7 , further comprising:
a second mixer coupled to the first input to frequency shift the audio signal based on a second selected reference frequency to produce a second frequency shifted audio signal.
12. The audio standard detection module of claim 11 , further comprising:
a second energy measurement module responsive to the second mixer to measure a second energy level of the second frequency shifted audio signal.
13. The audio standard detection module of claim 11 , wherein the audio signal is an intermediate frequency audio signal.
14. The audio standard detection module of claim 11 , wherein the audio signal is derived from a signal received via a television tuner.
15. An audio standard decision module, comprising:
an output to provide a plurality of reference frequencies to an energy detection module;
an input to receive a plurality, of measured energy levels corresponding to an input signal from the energy detection module, the plurality of measured energy levels corresponding to the plurality of reference frequencies; and
decision logic to determine a television audio standard based on the plurality of measured energy levels and based on the plurality of reference frequencies, the decision logic including a state machine, wherein the state machine includes a first state to provide a first reference frequency and to wait for a first energy measurement and a second state to store the first reference frequency.
16. The audio standard decision module of claim 15 , wherein the state machine further includes a third state to provide a second reference frequency and to wait for a second energy measurement and a fourth state to replace the stored first reference frequency with the second frequency in response to a determination that the second energy measurement is greater than the first energy measurement.
17. A method of processing a received signal to determine an audio signal standard, the method comprising:
multiplying an inter-carrier signal with a first set of functions to produce a first and a second frequency shifted signal;
filtering the first and the second frequency shifted signals to produce first and second filtered signals;
integrating the absolute value of each of the first and second filtered signals to produce first and second integrated signals;
measuring and storing an energy level of each of the first and the second integrated signals;
multiplying the inter-carrier signal with a second set of functions to produce a third and a fourth frequency shifted signal;
filtering the third and the fourth frequency shifted signals to produce third and fourth filtered signals;
integrating the absolute value of each of the third and the fourth filtered signals to produce third and fourth integrated signals;
measuring and storing an energy level of each of the third and the fourth integrated signals; and
selecting the audio signal standard in less than 13 milliseconds based on an evaluation of the stored energy levels.
18. The method of claim 17 , further comprising:
multiplying an inter-carrier signal with a third set of functions to produce a fifth and a sixth frequency shifted signal;
filtering the fifth and the sixth frequency shifted signals to produce fifth and sixth filtered signals;
integrating the absolute value of each of the fifth and sixth filtered signals to produce fifth and sixth integrated signals;
measuring and storing an energy level of each of the fifth and the sixth integrated signals;
multiplying the inter-carrier signal with a fourth set of functions to produce a seventh and an eighth frequency shifted signal;
filtering the seventh and the eighth frequency shifted signals to produce seventh and eighth filtered signals;
integrating the absolute value of each of the seventh and the eighth filtered signals to produce seventh and eighth integrated signals;
measuring and storing an energy level of each of the seventh and the eighth integrated signals;
multiplying an inter-carrier signal with a fifth set of functions to produce a ninth and a tenth frequency shifted signal;
filtering the ninth and the tenth frequency shifted signals to produce ninth and tenth filtered signals;
integrating the absolute value of each of the ninth and the tenth filtered signals to produce ninth and tenth integrated signals; and
measuring and storing an energy level of each of the ninth and the tenth integrated signals.
19. The method of claim 17 , wherein the first set of functions are sinusoidal functions.
20. The method of claim 17 , wherein the filtering is performed by a low pass filter.
21. A method of detecting an audio signal communicated in accordance with an audio standard, the method comprising:
determining a first energy level of an intermediate frequency audio signal to be demodulated with respect to at least one frequency of a first audio standard of a plurality of detectable audio standards;
determining a second energy level of the intermediate frequency audio signal to be demodulated with respect to at least one frequency of a second audio standard of the plurality of detectable audio standards; and
selecting one of the plurality of detectable audio standards based on the first and second determined energy levels in less than 13 milliseconds.
22. The method of claim 21 , further comprising demodulating the intermediate frequency audio signal using a frequency set associated with the selected one of the plurality of audio standards.
23. The method of claim 21 , wherein the intermediate frequency audio signal is a second intermediate frequency (SIF) audio signal.
24. The method of claim 21 , wherein the time to select one of the plurality of audio standards is substantially fixed regardless of which one of the plurality of audio standards is selected.
25. The method of claim 21 , further comprising:
configuring a audio standard detection module based on a selected audio standard.
26. The method of claim 21 , further comprising:
determining a first frequency corresponding to a highest measured energy level of a plurality of frequency shifted signals derived from the intermediate frequency audio signal;
determining a second frequency corresponding to a second highest measured energy level of the plurality of frequency shifted signals derived from intermediate frequency audio signal; and
wherein the one of the plurality of detectable audio standards is selected based on the first and the second frequency.
27. The method of claim 26 , further comprising:
comparing a first measured energy level to a threshold and comparing a second measured energy level to the threshold.
28. The method of claim 27 , wherein the threshold is approximately half of the second highest measured energy level.