Software based audio timing and synchronization

• US 10,602,468 B2
• Filed: 04/04/2019
• Issued: 03/24/2020
• Est. Priority Date: 02/21/2014
• Status: Active Grant

• Current Assignee: WISA Technologies Incorporated
• Original Assignee: Summit Wireless Technologies Inc.
• Inventors: Boehlke, Kenneth A., Davis, Harold T.
• Primary Examiner(s): Patel, Jay P
• Application Number:
  US16/375,392
• Publication Number:
  US 20190297589A1
• Time in Patent Office: 355 Days
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04N 21/43076 of the same content streams on multiple devices, e.g. when family members are watching the same movie on different devices
• CPC Class Codes: H04N 21/43637 involving a wireless protocol, e.g. Bluetooth, RF or wireless LAN [IEEE 802.11] arrangements for wireless networking or broadcasting of information in indoor or near-field type systems H04B10/114
• CPC Class Codes: H04R 2227/003 Digital PA systems using, e.g. LAN or internet
• CPC Class Codes: H04R 2420/07 Applications of wireless loudspeakers or wireless microphones
• CPC Class Codes: H04R 27/00 Public address systems circuits for preventing acoustic reaction H04R3/02; circuits for distributing signals to loudspeakers H04R3/12; monitoring or testing arrangements for public address systems H04R29/007; amplifiers H03F
• CPC Class Codes: H04R 5/04 Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments combinations of amplifiers H03F3/68; stereophonic systems H04S
• CPC Class Codes: H04W 56/001 Synchronization between nodes

Abstract

Synchronization of plural outputs of data transported by a wireless network is facilitated by band limiting a sample clock signal controlling a rate at which data is processed by the network'"'"'s devices and/or band limiting wall time data controlling the real time for presenting a datum.

Claims

1. An audio system comprising:

(a) a first listener including;

(i) a wall clock maintaining a wall time for occurrence of an event, said wall time updated by data transmitted by a master clock and received by said first listener;

(ii) a sample clock recoverer retrieving a sample clock from data received by said first listener from a talker, said sample clock regulating a processing rate for a datum included in said data received from said talker; and

(iii) a frequency filter bandlimiting said sample clock output by said sample clock recoverer, wherein said frequency filter comprises an estimator connected to receive said sample clock output by said sample clock recoverer; and

(iv) said estimator determining a frequency coefficient and a delay coefficient, said estimator settling the frequency coefficient and the delay coefficient, said estimator tracking and adjusting the frequency coefficient.

2. The audio system of claim 1 wherein the estimator measures the timing relationship between an internal counter of an audio subsystem processor and a time synchronization function.

3. The audio system of claim 2 wherein the estimator measures the timing relationship between the internal counter and the time synchronization function by multiplying the internal counter by the frequency coefficient then adding the delay coefficient to the result.

4. The audio system of claim 1 wherein the estimator adjusts the frequency coefficient and the delay coefficient.

5. The audio system of claim 4 wherein the estimator performs a delta ratio calculation on the time synchronization function and the internal counter and adaptively filters the result.

6. The audio system of claim 5 further comprising multiplying the output of the adaptive filter by the internal counter, then subtracting the result by the time synchronization function, then passing the result of the subtraction through an adaptive filter.

7. The audio system of claim 1 wherein the estimator tracks changes to the frequency coefficient and adjusts the frequency coefficient to eliminate frequency error.

8. The audio system of claim 1 wherein the estimator multiplies the internal counter by the frequency coefficient, adds the delay coefficient to the result of the multiplication, subtracts the time synchronization function from the result of the addition, divides the result of the subtraction by the internal counter, performs an AEC limiting function on the result of the division, adds the frequency coefficient to the result of the AEC limiting function, then stores the result of that addition as the frequency coefficient.

9. An audio system comprising:

(a) a first listener including;

(i) a wall clock maintaining a wall time for occurrence of an event, said wall time updated by a data transmitted by a master clock and received by said first listener;

(ii) a frequency filter bandlimiting said updating data received from said master clock and said wall time, wherein said frequency filter comprises an estimator connected to receive said updating data by said sample clock recoverer; and

(iii) said estimator determining a frequency coefficient and a delay coefficient, said estimator settling the frequency coefficient and the delay coefficient, said estimator tracking and adjusting the frequency coefficient; and

(audio echo cancellation function)

(iv) a sample clock recoverer retrieving a sample clock from data received by said first listener from a talker, said sample clock regulating a processing rate for a datum included in said data received from said talker.

10. The audio system of claim 9 wherein the estimator measures the timing relationship between an internal counter of an audio subsystem processor and a time synchronization function.

11. The audio system of claim 10 wherein the estimator measures the timing relationship between the internal counter and the time synchronization function by multiplying the internal counter by the frequency coefficient then adding the delay coefficient to the result.

12. The audio system of claim 9 wherein the estimator adjusts the frequency coefficient and the delay coefficient.

13. The audio system of claim 12 wherein the estimator performs a delta ratio calculation on the time synchronization function and the internal counter and adaptively filters the result.

14. The audio system of claim 13 further comprising multiplying the output of the adaptive filter by the internal counter, then subtracting the result by the time synchronization function, then passing the result of the subtraction through an adaptive filter.

15. The audio system of claim 9 wherein the estimator tracks changes to the frequency coefficient and adjusts the frequency coefficient to eliminate frequency error.

16. The audio system of claim 9 wherein the estimator multiplies the internal counter by the frequency coefficient, adds the delay coefficient to the result of the multiplication, subtracts the time synchronization function from the result of the addition, divides the result of the subtraction by the internal counter, performs an AEC limiting function on the result of the division, adds the frequency coefficient to the result of the AEC limiting function, then stores the result of that addition as the frequency coefficient.

17. A method for canceling audio echo in a network comprising the steps of:

(a) generating a filtered time synchronization function for the network; and

(b) settling a frequency coefficient and a delay coefficient for the network; and

(c) tracking the frequency coefficient and adjusting the frequency coefficient to compensate for drift within the network.

18. A method for canceling audio echo in a network comprising the steps of:

(a) measuring the timing relationship between an internal counter of an audio subsystem processor and a time synchronization function; and

(b) settling a frequency coefficient and a delay coefficient for the network; and

(c) tracking the frequency coefficient and adjusting the frequency coefficient to compensate for drift within the network.

19. A method for canceling audio echo in a network comprising the steps of:

(a) measuring a timing relationship between an internal counter of an audio subsystem processor and a time synchronization function; and

(b) settling a frequency coefficient and a delay coefficient for the network; and

(c) tracking the frequency coefficient and adjusting the frequency coefficient to compensate for drift within the network while constraining a frequency slew rate to be under an AEC limit.

20. A method for canceling audio echo in a network comprising the steps of:

(a) generating a filtered time synchronization function for the network; and

(b) performing a delta ratio calculation on the time synchronization function and an audio network internal counter, adaptively filtering the result of the delta ratio calculation, multiplying the output of the adaptive filtering by the internal counter, then subtracting the result of the multiplication by the time synchronization function, then adaptively filtering the result of the subtraction; and

(c) tracking the frequency coefficient and adjusting the frequency coefficient to compensate for drift within the network.

21. A method for canceling audio echo in a network comprising the steps of:

(a) generating a filtered time synchronization function for the network; and

(b) settling a frequency coefficient and a delay coefficient for the network; and

(c) multiplying an internal counter by the frequency coefficient, adding the delay coefficient to the result of the multiplication, subtracting the time synchronization function from the result of the addition, dividing the result of the subtraction by the internal counter, performing an AEC limiting function on the result of the division, adding the frequency coefficient to the result of the AEC limiting function, then storing the result of that addition as the frequency coefficient.

23. The method of claim 21 wherein the jitter reduction is performed by using N number of frequency samples to settle the frequency coefficient and the delay coefficient.

22. A method for reducing frequency error to zero in an audio network comprising the steps of:

(a) tracking a frequency coefficient and adjusting the frequency coefficient to compensate for drift; and

(b) determining a filtered time synchronization function for the audio network; and

(c) reducing jitter in the audio network by settling the frequency coefficient and the delay coefficient of the audio network.

24. The method of claim 22 wherein N is 1024.

26. The method of claim 24 wherein the frequency coefficient and the delay coefficient were obtained at the same time.

27. The method of claim 24 wherein the N filter length is a length sufficient to meet a preferred jitter reduction.

28. The method of claim 26 wherein the preferred jitter reduction is 32.

29. The method of claim 24 further comprising adjusting the frequency coefficient to compensate for changes in the oscillator of a Wi-Fi radio subsystem.

25. A method for seeding a delay coefficient and a frequency coefficient in an audio system to cancel audio echo comprising the steps of:

(a) determining a filtered time synchronization function by obtaining the frequency coefficient and the delay coefficient and measuring the coefficients against an internal counter; and

(b) processing and outputting the frequency coefficient and delay coefficient until a transient response of N filter length has settled; and

(c) adjusting the frequency coefficient to compensate for frequency drift.