Audio decoding device and compensation frame generation method

• US 8,725,501 B2
• Filed: 07/14/2005
• Issued: 05/13/2014
• Est. Priority Date: 07/20/2004
• Status: Active Grant

• Current Assignee: III Holdings 12, LLC (Intellectual Ventures LLC)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Ehara, Hiroyuki
• Primary Examiner(s): Desir, Pierre-Louis
• Assistant Examiner(s): KOVACEK, DAVID M
• Application Number:
  US11/632,770
• Publication Number:
  US 20080071530A1
• Time in Patent Office: 3,225 Days
• Field of Search: 704/200, 704/201, 704211-228, 704E19001-E19049, 704E21001-E2102, 375240-241, 455130-140
• US Class Current: 704/226
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation

Abstract

There is disclosed an audio decoding device capable of improving audio quality of a decoded signal by considering the energy change of a past signal in eracure concealment processing. In this device, an energy change calculation unit (143) calculates an average energy of an audio source signal of one-pitch cycle from the end of the ACB vector outputted from an adaptive codebook (106). Moreover, the energy change calculation unit (143) calculates a ratio of the average energy of the current sub-frame and the sub-frame immediately before and outputs the ratio to an ACB gain generation unit (135). The ACB gain generation unit (135) outputs a conceal processing ACB gain defined by the ACB gain decoded in the past or information on the energy change ratio outputted from the energy change calculation unit (143) to a multiplier (132).

Claims

1. A speech decoding apparatus configured as a circuit comprising:

an adaptive codebook that generates an excitation signal;

an average amplitude calculator that calculates an average amplitude for one pitch period from an end of the excitation signal stored in the adaptive codebook;

a memory that holds the calculated average amplitude;

an energy change rate calculator that calculates a ratio of a first average amplitude and a second average amplitude as an energy change rate, and smoothes the energy change rate over time, the first average amplitude being calculated by the average amplitude calculator with resect to a resent calculation target period the second average amplitude being calculated by the average amplitude calculator with respect to a calculation reference period earlier than the present calculation target period, and the second average amplitude being stored in the memory;

a decider that decides to set one of the smoothed energy change rate acquired in the energy change rate calculator and an adaptive codebook gain decoded before the present calculation target period as an adaptive codebook gain for processing

a generator that generates a signal for a lost frame by multiplying the excitation signal by the adaptive codebook gain for processing set by the decider with respect to the lost frame; and

a noise applier that applies noise to a high-frequency band of the generated signal,

wherein the noise applier determines voiced stationarity based at least on whether fluctuation of a decoding pitch period before the lost frame is large or small, and sets the high-frequency band as a frequency band to apply noise to when the voiced stationarity is determined to be low, or limits the frequency band to apply noise to, to a higher frequency part in the high-frequency band, when the voiced stationarity is determined to be high.

2. The speech encoding apparatus of claim 1, wherein the noise applier broadens the frequency band to which the noise is applied to a lower frequency band, in accordance with a consecutive number of lost frames.

3. A communication terminal apparatus comprising a speech decoding apparatus, the speech decoding apparatus being configured as a circuit comprising:

an adaptive codebook that generates an excitation signal;

an average amplitude calculator that calculates an average amplitude for one pitch period from an end of the excitation signal stored in the adaptive codebook;

a memory that holds the calculated average amplitude;

an energy change rate calculator that calculates a ratio of a first average amplitude and a second average amplitude, as an energy change rate, and smoothes the energy change rate over time, the first average amplitude being calculated by the average amplitude calculator with respect to a present calculation target period, the second average amplitude being calculated by the average amplitude calculator with respect to a calculation reference period earlier than the present calculation target period, and the second average amplitude being stored in the memory;

a decider that decides to set one of the smoothed energy change rate acquired in the energy change rate calculator and an adaptive codebook gain decoded before the present calculation target period as an adaptive codebook gain for processing;

a generator that generates a signal for a lost frame by multiplying the excitation signal by the adaptive codebook gain for processing set by the decider with respect to the lost frame; and

a noise applier that applies noise to a high-frequency band of the generated signal,

wherein the noise applier determines voiced stationarity based at least on whether fluctuation of a decoding pitch period before the lost frame is large or small, and sets the high-frequency band as a frequency band to apply noise to when the voiced stationarity is determined to be low, or limits the frequency band to apply noise to, to a higher frequency part in the high-frequency band, when the voiced stationarity is determined to be high.

4. A base station apparatus comprising a speech decoding apparatus, the speech decoding apparatus being configured as a circuit comprising:

an adaptive codebook that generates an excitation signal;

an average amplitude calculator that calculates an average amplitude for one pitch period from an end of the excitation signal stored in the adaptive codebook;

a memory that holds the calculated average amplitude;

an energy change rate calculator that calculates a ratio of a first average amplitude and a second average amplitude, as an energy change rate, and smoothes the energy change rate over time, the first average amplitude being calculated by the average amplitude calculator with respect to a present calculation target period, the second average amplitude being calculated by the average amplitude calculator with respect to a calculation reference period earlier than the present calculation target period, and the second average amplitude being stored in the memory;

a decider that decides to set one of the smoothed energy change rate acquired in the energy change rate calculator and an adaptive codebook gain decoded before the present calculation target period as an adaptive codebook gain for processing;

a generator that generates a signal for a lost frame by multiplying the excitation signal by the adaptive codebook gain for processing set by the decider with respect to the lost frame; and

a noise applier that applies noise to a high-frequency band of the generated signal,

wherein the noise applier determines voiced stationarity based at least on whether fluctuation of a decoding pitch period before the lost frame is large or small, and sets the high-frequency band as a frequency band to apply noise to when the voiced stationarity is determined to be low, or limits the frequency band to apply noise to, to a higher frequency part in the high-frequency band, when the voiced stationarity is determined to be high.

5. A speech decoding method comprising:

an average amplitude calculating step of calculating an average amplitude for one pitch period from an end of an excitation signal stored in an adaptive codebook;

a holding step of holding the calculated average amplitude;

an energy change rate calculating step of calculating a ratio of a first average amplitude and a second average amplitude, as an energy change rate, and smoothing the energy change rate over time, the first average amplitude being calculated in the average amplitude calculating step with respect to a present calculation target period, the second average amplitude being calculated in the average amplitude calculating step with respect to a calculation reference period earlier than the present calculation target period and held;

a deciding step of deciding to set one of the smoothed energy change rate acquired in the energy change rate calculating step and an adaptive codebook gain decoded before the present calculation target period, as an adaptive codebook gain for processing

a generating step of generating a signal for a lost frame by multiplying the excitation signal by the adaptive codebook gain for processing determined in the deciding step with respect to the lost frame; and

a noise applying step of applying noise to a high-frequency band of the generated signal,

wherein, in the noise applying step, voiced stationarity is determined based at least on whether fluctuation of a decoding pitch period before the lost frame is large or small, and the high-frequency band is set as a frequency band to apply noise to when the voiced stationarity is determined to be low, or the frequency band to apply noise to is limited to a higher frequency part in the high-frequency band, when the voiced stationarity is determined to be high.