Signal encoding and decoding system using auditory parameters and bark spectrum

• US 5,864,794 A
• Filed: 10/09/1997
• Issued: 01/26/1999
• Est. Priority Date: 03/18/1994
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation), Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Tasaki, Hirohisa
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): Chawan, Vijay B.
• Application Number:
  US08/947,765
• Time in Patent Office: 474 Days
• Field of Search: 395/2.2, 395/2.14
• US Class Current: 704/200.1
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 2021/02168 the estimation exclusively taking place during speech pauses
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: G10L 21/0264 characterised by the type of parameter measurement, e.g. correlation techniques, zero crossing techniques or predictive techniques
• CPC Class Codes: G10L 25/27 characterised by the analysis technique

Abstract

A signal encoding system A1 includes a bark spectrum calculating device 2 for calculating a bark spectrum as a parameter based on an auditory model, a bark spectrum encoding device 3 for encoding the bark spectrum, a sound source calculating device 4 and a sound source encoding device 5. The bark spectrum calculating device 2 includes a power spectrum calculating device 6, a critical band integrating device 7, an equal loudness compensating device 8 and a loudness converting device 9. These devices are formed by engineering the functions and effects which are similar to those of the auditory model. The decoding process perform the conversion in the opposite direction. As a result, the signals can be encoded and decoded through less calculation in a manner well matching the human auditory characteristics. When speech signals are to be encoded, it can be realized through less calculation and memory while suppressing noise components other than the speech signal.

Claims

1. A signal encoding system comprising:

auditory model parameter calculating means for calculating a parameter based on an auditory model to form an output auditory model parameter; and

auditory model parameter encoding means for encoding the auditory model parameter to form an output encoded auditory model parameter wherein the auditory model parameter calculating means comprises;

power spectrum calculating means for calculating the power spectrum of an input signal;

critical band integrating means for multiplying the power spectrum calculated by the power spectrum calculating means by a critical band filter function to calculate a pattern of excitation;

equal loudness compensating means for multiplying the pattern of excitation calculated by the critical band integrating means by a compensation factor representing the relationship between the magnitude and equal loudness of a sound for every frequency to calculate a compensated excitation pattern; and

loudness converting means for converting the power scale of the compensated excitation pattern calculated by the equal loudness compensating means into a sone scale to calculate a Bark spectrum.

2. A signal encoding system as defined in claim 1, further comprising:

sound-existence judging means for judging an input signal with respect to whether it represents speech activity or non-speech activity;

probable noise parameter calculating means for calculating the average auditory model parameter of noise from a plurality of said auditory model parameters to form an output probable noise parameter when the input signal represents non-speech activity; and

noise removing means for removing a component corresponding to said probable noise parameter from said auditory model parameter when the input signal represents speech activity.

3. A signal encoding system as defined in claim 1, further comprising:

sound-existence judging means for judging an input signal with respect to whether it represents speech activity or non-speech activity; and

probable noise parameter calculating means for calculating the average auditory model parameter of noise from a plurality of said auditory model parameters to form an output probable noise parameter when the input signal represents non-speech activity.

9. A signal encoding system as defined in claim 2, further comprising:

sound-existence judging means for judging the input signal with respect to whether it represents speech activity or non-speech activity;

probable noise parameter calculating means for calculating the average auditory model parameter of noise from a plurality of said auditory model parameters to form an output probable noise parameter when the input signal represents non-speech activity; and

noise removing means for removing a component corresponding to said probable noise parameter from said auditory model parameter when the input signal represents speech activity.

4. A signal encoding system which encodes an input signal, the signal encoding system comprising:

auditory model parameter calculating means for calculating a parameter based on an auditory model to form an output auditory model parameter;

auditory model parameter encoding means for encoding the auditory model parameter to form an output encoded auditory model parameter;

auditory model parameter decoding means for decoding the encoded auditory model parameter to form an output decoded auditory model parameter;

converter means for converting said decoded auditory model parameter into a parameter representing the form of a frequency spectrum to form an output frequency spectrum parameter;

a sound source codebook storing a plurality of sound source codewords; and

sound source codeword selecting means for calculating a weight factor from said encoded auditory model parameter and for calculating a weighted distance between each of the sound source codewords in said sound source codebook multiplied by said frequency spectrum parameter and the input signal in a frequency band using said weight factor to select and output one of said sound source codewords having the minimum weighted distance.

5. A signal encoding system as defined in claim 4 wherein it uses a bark spectrum as an auditory model parameter.

6. A signal encoding system as defined in claim 5, further comprising:

sound-existence judging means for judging the input signal with respect to whether it represents speech activity or non-speech activity;

probable noise parameter calculating means for calculating the average auditory model parameter of noise from a plurality of said auditory model parameters to form an output probable noise parameter when the input signal represents non-speech activity; and

noise removing means for removing a component corresponding to said probable noise parameter from said auditory model parameter when the input signal represents speech activity.

7. A signal encoding system as defined in claim 5 wherein the auditory model parameter calculating means comprises:

power spectrum calculating means for calculating the power spectrum of an input signal;

critical band integrating means for multiplying the power spectrum calculated by the power spectrum calculating means by a critical band filter function to calculate a pattern of excitation;

equal loudness compensating means for multiplying the pattern of excitation calculated by the critical band integrating means by a compensation factor representing the relationship between the magnitude and equal loudness of a sound for every frequency to calculate a compensated excitation pattern; and

loudness converting means for converting the power scale of the compensated excitation pattern calculated by the equal loudness compensating means into a sone scale to calculate a bark spectrum.

8. A signal encoding system as defined in claim 5, further comprising:

sound-existence judging means for judging the input signal with respect to whether it represents speech activity or non-speech activity; and

probable noise parameter calculating means for calculating the average auditory model parameter of noise from a plurality of said auditory model parameters to form an output probable noise parameter when the input signal represents non-speech activity and wherein the auditory model parameter calculating means comprises;

power spectrum calculating means for calculating the power spectrum of the input signal;

critical band integrating means for multiplying the power spectrum calculated by the power spectrum calculating means by a critical band filter function to calculate a pattern of excitation;

equal loudness compensating means for multiplying the pattern of excitation calculated by the critical band integrating means by a compensation factor representing the relationship between the magnitude and equal loudness of a sound for every frequency to calculate a compensated excitation pattern;

removing a noise component corresponding to said probable noise parameter from a compensated excitation pattern to calculate a compensated excitation pattern without noise when the input signal represents speech activity; and

loudness converting means for converting the power scale of the compensated excitation pattern without noise into a sone scale to calculate a bark spectrum.

10. A signal encoding system as defined in claim 4, further comprising:

sound-existence judging means for judging the input signal with respect to whether it represents speech activity or non-speech activity; and

probable noise parameter calculating means for calculating the average auditory model parameter of noise from a plurality of said auditory model parameters to form an output probable noise parameter when the input signal represents non-speech activity and wherein the auditory model parameter calculating means comprises;

power spectrum calculating means for calculating the power spectrum of the input signal;

critical band integrating means for multiplying the power spectrum calculated by the power spectrum calculating means by a critical band filter function to calculate a pattern of excitation;

equal loudness compensating means for multiplying the pattern of excitation calculated by the critical band integrating means by a compensation factor representing the relationship between the magnitude and equal loudness of a sound for every frequency to calculate a compensated excitation pattern;

removing a noise component corresponding to said probable noise parameter from a compensated excitation pattern;

removing a noise component corresponding to said probable noise parameter from a compensated excitation pattern to calculate a compensated excitation pattern without noise when the input signal represents speech activity; and

loudness converting means for converting the power scale of the compensated excitation pattern without noise into a sone scale to calculate a bark spectrum.

11. A signal encoding system as defined in claim 4 wherein the auditory model parameter is a bark spectrum, the frequency spectrum parameter being a frequency spectrum amplitude value, said conversion means being operative to represent the frequency spectrum amplitude value using an approximate formula with a central frequency spectrum amplitude value of the same order as that of the bark spectrum and solving simultaneous equations between the bark spectrum and the central frequency spectrum amplitude value through said approximate formula, thereby converting the bark spectrum into the central frequency spectrum amplitude value, and said central frequency spectrum amplitude value and said approximate formula being used to calculate the frequency spectrum amplitude value.

12. A signal decoding system comprising:

auditory model parameter decoding means for decoding a auditory model parameter encoded from a parameter based on an auditory model to form a decoded auditory model parameter;

converting means for converting said auditory model parameter into a parameter representing the form of a frequency spectrum to form an output frequency spectrum parameter; and

synthesis means for generating a decoded signal from said frequency spectrum parameter wherein said converting means comprises;

loudness inverse-conversion means for converting the sone scale of the Bark spectrum into the power scale to calculate a compensated excitation pattern;

equal loudness inverse-compensation means for multiplying said compensated excitation pattern by the inverse number of a compensation factor representing the relationship between the magnitude and equal loudness of a sound for every frequency to calculate an excitation pattern;

power spectrum conversion means for calculating a power spectrum from said excitation pattern and a critical band filter function; and

square root means for calculating a square root for each component in said power spectrum to calculate a frequency spectrum amplitude value.

13. A signal decoding system as defined in claim 12 wherein a bark spectrum is used as an auditory model parameter.

14. A signal decoding system as defined in claim 13 wherein a frequency spectrum amplitude value is used as a frequency spectrum parameter.

15. A signal decoding system as defined in claim 12 wherein a frequency spectrum amplitude value is used as a frequency spectrum parameter.

16. A signal decoding system as defined in claim 12 wherein the auditory model parameter is a bark spectrum, the frequency spectrum parameter being a frequency spectrum amplitude value, said conversion means being operative to represent the frequency spectrum amplitude value using an approximate formula with a central frequency spectrum amplitude value of the same order as that of the bark spectrum and solving simultaneous equations between the bark spectrum and the central frequency spectrum amplitude value through said approximate formula, thereby converting the bark spectrum into the central frequency spectrum amplitude value, and said central frequency spectrum amplitude value and said approximate formula being used to calculate the frequency spectrum amplitude value.