Method and apparatus for extending the bandwidth of a speech signal

A bandwidth extension module suitable for use in artificially extending the bandwidth of a lowband speech signal, comprising:

• means for band-pass filtering the lowband speech signal to obtain a band-pass signal;
• means for pitch-synchronously modulating said band-pass signal about at least one carrier frequency to obtain a highband speech signal component;
• means for determining a highband speech signal based on said highband speech signal component;
• means for combining said lowband speech signal with said highband speech signal to obtain a bandwidth-extended speech signal.

A computer-readable storage medium comprising computer-readable program code which, when interpreted by a computing apparatus, causes the computing apparatus to execute a method of artificially extending the bandwidth of a lowband speech signal, the computer-readable program code comprising:

• first computer-readable program code for causing the computing apparatus to obtain a band-pass signal by band-pass filtering the lowband speech signal;
• second computer-readable program code for causing the computing apparatus to obtain a highband speech signal component by pitch-synchronously modulating said band-pass signal about at least one carrier frequency;
• third computer-readable program code for causing the computing apparatus to determine a highband speech signal based on said highband speech signal component;
• fourth computer-readable program code for causing the computing apparatus to obtain a bandwidth-extended speech signal by combining said lowband speech signal with said highband speech signal.

A bandwidth extension module suitable for use in artificially extending the bandwidth of a lowband speech signal, comprising:

• a band-pass filter configured to produce a band-pass signal from the lowband speech signal;
• at least one carrier frequency modulator, each said carrier frequency modulator configured to pitch-synchronously modulate said band-pass signal about a respective carrier frequency, the at least one carrier frequency modulator collectively producing a highband speech signal component;
• a synthesis filter configured to determine a highband speech signal based on said highband speech signal component;
• a summation module configured to combine said lowband speech signal with said highband speech signal to obtain a bandwidth-extended speech signal.

An excitation signal generator, comprising:

• a bandpass filter configured to produce a band-pass signal from the lowband speech signal;
• a modulator bank comprising a plurality of carrier frequency modulators, each of said carrier frequency modulators configured to frequency shift the band-pass signal to a respective carrier frequency associated with the respective carrier frequency modulator, thereby to produce a respective one of a plurality of modulated signals;
• a summation module configured to combine the modulated signals into an excitation signal for use in generating a highband speech signal that complements the lowband speech signal in a highband frequency range;
• the carrier frequency associated with a given one of the carrier frequency modulators being selected based on a pitch of the lowband speech signal to ensure pitch-synchronicity between the bandpass signal and the respective modulated signal produced by the given one of the carrier frequency modulators.

A bandwidth extension module, comprising:

• an input for receiving a first speech signal having first frequency content in a first frequency range;
• a processing entity comprising:
• a band-pass filter configured to produce a band-pass signal from the first speech signal;
• at least one carrier frequency modulator, each said carrier frequency modulator configured to pitch-synchronously modulate said band-pass signal about a respective carrier frequency, the at least one carrier frequency modulator collectively producing a highband speech signal component;
• a synthesis filter configured to determine a highband speech signal based on said highband speech signal component;
• and
• a summation module configured to combine said first speech signal with said highband speech signal to obtain said second speech signal;
• an output for producing a second speech signal having second frequency content in a second frequency range that includes an additional frequency range outside the first frequency range;
• and
• wherein when the first frequency content contains harmonics in the first frequency range obeying a harmonic relationship, said processing entity is configured to cause the second frequency content to contain harmonics in the first frequency range and in the additional frequency range that collectively obey said harmonic relationship.