System for sampling rate conversion in digital audio applications

• US 6,661,357 B2
• Filed: 11/27/2002
• Issued: 12/09/2003
• Est. Priority Date: 07/31/2001
• Status: Expired due to Fees

• Current Assignee: Wind River Systems Incorporated (Aptiv PLC)
• Original Assignee: Wind River Systems Incorporated (Aptiv PLC)
• Inventors: Bland, Dennis
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Mai, Lam T.
• Application Number:
  US10/305,534
• Publication Number:
  US 20030076247A1
• Time in Patent Office: 377 Days
• Field of Search: 341/61, 341/50, 341/123, 704/219, 704/223, 704/224
• US Class Current: 341/61
• CPC Class Codes: G10L 19/0204 using subband decomposition

Abstract

A method for upsampling a digital audio signal is described. The method includes receiving a first digital audio signal including samples and having a first sampling rate. The method also includes outputting at least one sample from the first digital audio signal as part of a second digital audio signal, the second digital audio signal having a desired second sampling rate, the second sampling rate being higher than the first sampling rate. The method also includes incrementing a counter for each sample from the first digital audio signal that is output as part of the second digital audio signal. The method also includes, when the counter exceeds a threshold number, inserting at least one synthetic sample as part of the second digital audio signal. The method also includes repeating the outputting, incrementing, and inserting until all the samples in the first digital audio signal have been output.

Claims

1. A system, comprising:

a processor;

at least one storage system coupled to the processor;

an audio output control mechanism stored in the at least one storage system and configured to receive a first digital audio signal having samples;

an audio input control mechanism stored in the at least one storage system and configured to receive a third digital audio signal having samples;

an upsampling mechanism stored in the at least one storage system and configured to

(a) determine a first sampling rate of the first digital audio signal,

(b) output at least one sample from the first digital audio signal as part of a second digital audio signal, the second digital audio signal having a second sampling rate, the second sample rate being higher than the first sampling rate,

(c) increment a first counter for each sample from the first digital audio signal that is output as part of the second digital audio signal,

(d) insert at least one synthetic sample as part of the second digital audio signal when the first counter exceeds a first threshold number,

(e) repeat (b), (c) and (d) until all samples in the first digital audio signal have been output; and

a downsampling mechanism stored in the at least one storage system and configured to

(f) determine a third sampling rate of the third digital audio signal,

(g) output at least one sample from the third digital audio signal as part of a fourth digital audio signal, the fourth digital audio signal having a fourth sampling rate, the fourth sample rate being lower than the third sampling rate,

(h) increment a third counter for each sample from the third digital audio signal that is output as part of the fourth digital audio signal,

(i) skip at least one sample from the third digital audio signal when the third counter exceeds a second threshold number,

(j) repeat (g), (h) and (i) until all samples in the third digital audio signal have been outputted or skipped.

2. The system of claim 1, further comprising:

an upsampling data structure stored in the storage system, accessible by the upsampling mechanism, and including

a first variable to store the first threshold number,

a second variable to store a value used to increment the first counter,

a third variable to store the first counter,

a fourth variable to store a second counter to track the samples of the first digital audio signal, and

a fifth variable to store a third counter to track the samples of the second digital audio signal.

3. The system of claim 2, wherein the value used to increment the first counter is a function of the ratio of the first sampling rate and the second sampling rate.

4. The system of claim 2, wherein the upsampling data structure further includes at least one scale factor.

5. The system of claim 2, wherein the upsampling data structure is stored in the at least one storage system as one of a list and a table.

6. The system of claim 1, wherein the first digital audio signal is stored in the at least one storage system.

7. The system of claim 1, further comprising an operating system stored in the at least one storage system and configured to control the operation of the processor.

8. The system of claim 1, further comprising:

an audio output device coupled to the processor;

wherein the audio output control mechanism is further configured to control the audio output device.

9. The system of claim 8, wherein the second digital audio signal is output to the audio output control mechanism, and provided by the audio output control mechanism to the audio output device.

10. The system of claim 1, further comprising:

a downsampling data structure stored in the storage system and including

a sixth variable to store the second threshold number,

a seventh variable to store a value used to increment the third counter,

an eighth variable to store a number of samples to skip,

a ninth variable to store the third counter, and

a tenth variable to store a fourth counter to track the samples of the third digital audio signal.

11. The system of claim 10, wherein the value used to increment the third counter is a function of the ratio of the third sampling rate and the fourth sampling rate.

12. The system of claim 10, wherein the downsampling data structure is stored in the at least one storage system as one of a list and a table.

13. The system of claim 10, wherein the fourth digital audio signal is stored in the at least one storage system.

14. The system of claim 10, wherein the third digital audio signal is stored in the at least one storage system.

15. The system of claim 10, further comprising:

an audio input device coupled to the processor;

wherein the third digital audio signal is received by the audio input device and provided to the audio input control mechanism.

16. A system, comprising:

a processor;

an audio output system coupled to the processor; and

an upsampling software facility configured to

(a) determine a first sampling rate of a first digital audio signal,

(b) output at least one sample from the first digital audio signal as part of a second digital audio signal, the second digital audio signal having a second sampling rate, the second sample rate being higher than the first sampling rate,

(c) increment a first counter for each sample from the first digital audio signal that is output as part of the second digital audio signal,

(d) insert at least one synthetic sample as part of the second digital audio signal when the first counter exceeds a threshold number,

(e) repeat (b), (c) and (d) until all samples in the first digital audio signal have been output;

wherein the processor is configured to execute the upsampling software facility and provide the second digital audio signal to the audio output system.

17. The system of claim 16, wherein the audio output system includes an audio output device.

18. The system of claim 17, wherein the audio output device is at least one of a speaker or headphones.

19. A system, comprising:

a processor;

an audio input system coupled to the processor; and

a downsampling software facility configured to

(a) determine a first sampling rate of the first digital audio signal,

(b) output at least one sample from the first digital audio signal as part of a second digital audio signal, the second digital audio signal having a second sampling rate, the second sample rate being lower than the first sampling rate,

(c) increment a first counter for each sample from the first digital audio signal that is output as part of the second digital audio signal,

(d) skip at least one sample from the first digital audio signal when the first counter exceeds a threshold number,

(e) repeat (b), (c) and (d) until all samples in the first digital audio signal have been outputted or skipped;

wherein the processor is configured to receive the first digital audio signal from the audio input system and execute the downsampling software facility.

20. The system of claim 19, wherein the audio input system includes an audio input device.