Transmission system with speech encoder with improved pitch detection

• US 5,963,895 A
• Filed: 05/10/1996
• Issued: 10/05/1999
• Est. Priority Date: 05/10/1995
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Taori, Rakesh, Kathmann, Eric, Sluijter, Robert J.
• Primary Examiner(s): Dorvil, Richemond
• Application Number:
  US08/645,544
• Time in Patent Office: 1,243 Days
• Field of Search: 395/2.25, 395/2.16, 395/2.17, 395/2.26, 395/2.27, 704/216, 704/207, 704/208, 704/217, 704/218, 704/205, 704/209
• US Class Current: 704/207
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

A transmission system contains a speech coder which utilizes a pitch detector that is arranged to select a characteristic auxiliary signal portion from the signal to be coded in order to improve the quality of the pitch detection. The pitch is found by searching in the speech signal for signal portions that correspond to the characteristics auxiliary signal portion and by calculating the time difference between the respective signal portions.

Claims

1. A transmission system comprising:

a transmitter including an encoder for deriving a coded signal from a quasi-periodic signal, the transmitter being arranged for transmitting the coded signal to a receiver via a transmission medium, the encoder comprising a pitch detector for deriving pitch information from the quasi-periodic signal, wherein the pitch detector comprises selecting means for selecting a characteristic auxiliary portion of an auxiliary signal, that is representative of the quasi-periodic signal, search means for searching for at least a further signal portion of the auxiliary signal that sufficiently corresponds to the characteristic auxiliary signal portion, and means for deriving the pitch information from the instants at which the characteristic auxiliary signal portion and the further signal portion occur.

2. The transmission system as claimed in claim 1, wherein the characteristic auxiliary signal portion comprises a signal portion that has maximum energy over a certain time segment.

3. The transmission system as claimed in claim 2, wherein the duration of the characteristic auxiliary signal portion is smaller than or equal to the briefest occurring pitch period.

4. The transmission system as claimed in claim 2, wherein the search means comprise correlation means for calculating the correlation between the characteristic auxiliary signal portion and the auxiliary signal, the pitch information being represented by the position of the peaks in the correlation function.

5. The transmission system as claimed in claim 1, wherein the duration of the characteristic auxiliary signal portion is smaller than or equal to the briefest occurring pitch period.

6. The transmission system as claimed in claim 3, wherein the search means comprise correlation means for calculating the correlation between the characteristic auxiliary signal portion and the auxiliary signal, the pitch information being represented by the position of the peaks in the correlation function.

7. The transmission system as claimed in claim 1, wherein the search means comprise correlation means for calculating the correlation between the characteristic auxiliary signal portion and the auxiliary signal, the pitch information being represented by the position of the peaks in the correlation function.

8. The transmission system as claimed in claim 7, wherein the pitch detector comprises means for calculating the surface of the peaks in the correlation function, the pitch detector deriving the pitch information from the surface of the peaks of the correlation function plotted against time.

9. The transmission system as claimed in claim 8, wherein the pitch detector comprises expansion means for converting the surface of the peaks of the correlation function into expanded surface values of the peaks of the correlation function.

10. Encoder for deriving a coded signal from a quasi-periodic signal, the encoder comprising a pitch detector for deriving pitch information from the quasi-periodic signal, characterized in that the pitch detector comprises selecting means for selecting a characteristic auxiliary portion of an auxiliary signal, which auxiliary signal is representative of the quasi-periodic signal, search means for searching for at least a further signal portion of the auxiliary signal that sufficiently corresponds to the characteristic auxiliary signal portion, and means for deriving the pitch information from the instants at which the characteristic auxiliary signal portion and the further signal portion occur.

11. The encoder as claimed in claim 10, wherein the characteristic auxiliary signal portion comprises a signal portion that has maximum energy over a certain time segment.

12. Arrangement for calculating the period of a quasi-periodic signal, comprising selecting means for selecting a characteristic auxiliary portion of an auxiliary signal which is representative of the quasi-periodic signal, search means for searching for at least a further signal portion of the auxiliary signal that sufficiently corresponds to the characteristic auxiliary signal portion, and means for deriving the pitch information from the instants at which the characteristic auxiliary signal portion and the further signal portion occur.

13. Coding method for deriving a coded signal from a quasi-periodic signal which comprises:

selecting a characteristic auxiliary portion of an auxiliary signal which auxiliary signal is representative of the quasi-periodic signal, searching at least for a further signal portion of the auxiliary signal that sufficiently corresponds to the characteristic auxiliary signal portion, and deriving pitch information from the instants at which the characteristic auxiliary signal portion and the further signal portion occur.

14. A pitch detector for deriving pitch information from a quasi-periodic signal comprising:

means for deriving from the quasi-periodic signal an auxiliary signal representative of the quasi-periodic signal,

energy measuring means responsive to the auxiliary signal so as to produce a signal E n! calculated as a running energy function of a segment of the auxiliary signal,

selecting means responsive to the auxiliary signal and to the signal E n! thereby to select a characteristic auxiliary portion of the auxiliary signal,

search means responsive to the characteristic auxiliary signal portion and to the auxiliary signal for searching for at least a further signal portion of the auxiliary signal that sufficiently corresponds to the characteristic auxiliary signal portion, and

means coupled to an output of the search means for deriving the pitch information from the instants at which the characteristic auxiliary signal portion and the further signal portion occur.

15. The pitch detector as claimed in claim 14 wherein the search means comprise correlation means for calculating the correlation between the characteristic auxiliary signal portion and the auxiliary signal, the pitch information being represented by the position of peaks in the correlation function.

16. The pitch detector as claimed in claim 15 wherein the pitch information deriving means comprises means for calculating the surface of the peaks in the correlation function, the pitch information being derived from the surface of the peaks of the correlation function plotted against time.

17. The pitch detector as claimed in claim 16 further comprising expansion means coupled to an output of the means for calculating the surface peaks in the correlation function for converting the surface of the peaks of the correlation function into expanded surface values of the peaks of the correlation function.

18. The pitch detector as claimed in claim 15 wherein the pitch information deriving means comprises an integrator coupled to an output of the correlation means.

19. The pitch detector as claimed in claim 14 wherein the selecting means supplies a characteristic auxiliary signal portion that comprises a signal portion that has maximum energy over a certain time segment.

20. The pitch detector as claimed in claim 14 further comprising:

an envelope detector responsive to said auxiliary signal, and

a controllable amplifier having input means that receive said auxiliary signal and an output signal of the envelope detector and supplies to the search means an amplitude controllable auxiliary signal.