Method and apparatus for evaluating an audio decoder

• US 6,138,051 A
• Filed: 01/22/1997
• Issued: 10/24/2000
• Est. Priority Date: 01/23/1996
• Status: Expired due to Fees

• Current Assignee: Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Dieterich, Charles B.
• Primary Examiner(s): CHIN, VIVIAN C
• Application Number:
  US08/787,429
• Time in Patent Office: 1,371 Days
• Field of Search: 381/2, 381/58, 381/60, 381/59, 381/22, 364/400.01, 375/242, 375/224, 375/225, 375/228, 704/201, 700/94, 371/30, 324/542, 324/500, 324/510, 324/527, 379/1, 379/6
• US Class Current: 700/94
• CPC Class Codes: G10L 25/69 for evaluating synthetic or decoded voice signals
• CPC Class Codes: H04B 1/665 using psychoacoustic properties of the ear, e.g. masking effect

Abstract

A method and apparatus for creating a plurality of encoded bitstreams that represent selected waveforms in different ways such that when an audio decoder decodes the bitstream, an audible tone or lack thereof, will signify the failure of the audio decoder. The method employs a waveform having a set of baseline parameters but encodes the waveform in different ways by varying the parameter under test. The method monitors the audio decoder'"'"'s ability to properly decode these alternating waveforms, by listening for an audible tone change or lack thereof. Since the behavior of the selected waveform is predictable, the method provides a set of simple and effective tests for evaluating black box audio decoders which may have no accessible internal nodes.

Claims

1. A method of evaluating an audio decoder, comprising the steps of:

(a) sending an encoded audio bitstream to the audio decoder;

(b) decoding said encoded audio bitstream by the audio decoder; and

(c) observing an auditory sign corresponding to said encoded audio bitstream to evaluate the performance of the audio decoder.

2. The method of claim 1, wherein said encoded audio bitstream comprises an encoded sinewave and wherein said auditory sign comprises an audible tone if the audio decoder correctly decodes the encoded audio bitstream and a silence or noise if the audio decoder incorrectly decodes the encoded audio bitstream.

3. The method of claim 1, wherein said encoded audio bitstream comprises a waveform having a predefined peak amplitude and wherein said waveform is encoded using a set of scalefactors such that said predefined peak amplitude is maintained.

4. The method of claim 1, wherein said encoded audio bitstream comprises a waveform encoded with alternating scfsi values, an initial scfsi value and a second scfsi value.

5. The method of claim 1, wherein said encoded audio bitstream comprises a waveform encoded with alternating quantization levels, a reference quantization level and a test quantization level.

6. The method of claim 1, wherein said encoded audio bitstream comprises a waveform encoded with alternating stereo modes.

7. The method of claim 1, wherein said encoded audio bitstream comprises a anti-mono signal comprising two waveforms of equal amplitude and opposite phase.

8. The method of claim 1, wherein said encoded audio bitstream comprises a waveform encoded with alternating sample rates.

9. The method of claim 1, wherein said encoded audio bitstream comprises a waveform encoded with alternating types of de-emphasis.

10. The method of claim 1, wherein said encoded audio bitstream comprises a waveform encoded with a valid CRC-check word and said waveform encoded with an invalid CRC-check word.

11. The method of claim 1, wherein said sending step (a) comprises the steps of:

(a1) sending an encoded audio bitstream having a waveform which is encoded using a plurality of parameters;

(a2) changing a value of at least one of said plurality of parameters; and

wherein said observing step (c) comprises the step of detecting a change in said auditory sign in response to said change in parameter.

12. An audio bitstream in a computer-readable medium for testing an audio decoder comprising a first waveform encoded with a plurality of parameters for producing an auditory sign, where a value of at least one of said plurality of parameters is changed to evaluate the audio decoder.

13. The audio bitstream of claim 12, wherein said first waveform is encoded with a scfsi parameter having a plurality of scfsi values, where said first waveform is encoded with alternating scfsi values separated by a period of silence.

14. The audio bitstream of claim 12, wherein said plurality of parameters includes a quantization parameter having a plurality of quantization levels, where said first waveform is encoded with alternating quantization levels producing a quantized waveform that is identical in all of said quantization levels.

15. The audio bitstream of claim 12, wherein said plurality of parameters includes a stereo mode parameter having a plurality of stereo modes, where said first waveform is encoded with alternating stereo modes producing an encoded waveform that is identical in all of said stereo modes.

16. The audio bitstream of claim 12, further comprises a second waveform, where said waveforms have equal amplitude and opposite phase, wherein said waveforms are encoded to opposing channels for each of a plurality of frequency ranges such that all of said plurality of frequency ranges are tested.

17. The audio bitstream of claim 12, wherein said plurality of parameters includes a sample rate parameter having a plurality of sample rates, where said first waveform is encoded with alternating sample rates separated by a period of silence.

18. The audio bitstream of claim 12, wherein said first waveform is further encoded with a pre-emphasis parameter having a plurality of de-emphasis types, where said first waveform is encoded with alternating de-emphasis types separated by a period of silence.

19. The audio bitstream of claim 12, wherein said first waveform is further encoded with a CRC-check parameter having a correct CRC-check word, where said first waveform is encoded with alternating correct CRC-check word and an incorrect CRC-check word.

20. An apparatus for testing an audio decoder comprising:

means for generating an encoded audio bitstream;

means, coupled to said generating means, for sending said encoded audio bitstream to the audio decoder; and

means, coupled to the audio decoder, for observing an auditory sign corresponding to said encoded audio bitstream to evaluate the performance of the audio decoder.