Classification between time-domain coding and frequency domain coding
A method for processing speech signals prior to encoding a digital signal comprising audio data includes selecting frequency domain coding or time domain coding based on a coding bit rate to be used for coding the digital signal and a short pitch lag detection of the digital signal.
1. A method performed by an encoder for processing speech signals prior to encoding a digital signal comprising audio data, comprising:
receiving the digital signal that is to be encoded; and
selecting time domain coding based on
a coding bit rate to be used for coding the digital signal is less than a first bit rate limit; and
detecting that the digital signal comprises a short pitch signal for which the pitch lag is shorter than a pitch lag limit, wherein the pitch lag limit is a minimum allowable pitch for a Code Excited Linear Prediction Technique (CELP) algorithm for coding the digital signal.
2. The method of claim 1 , wherein the minimum allowable pitch is 34 when a sampling rate is 12.8 kHz.
3. The method of claim 1 , wherein the first bit rate limit is 24.4 kbps.
4. The method of claim 1 , further comprising:
selecting frequency domain coding for coding the digital signal based on:
coding bit rate is greater than the first bit rate limit.
5. The method of claim 1 , wherein detecting the digital signal comprises a short pitch signal comprises:
detecting the digital signal comprises the short pitch signal based on a parameter for detecting lack of very low frequency energy or a parameter for spectral sharpness.
6. An encoder for processing speech signals prior to encoding a digital signal comprising audio data, the encoder comprising:
a memory storing computer instructions;
a processor coupled to retrieve and execute the computer instructions to prompt the processor to perform the steps of:
receiving the digital signal that is to be encoded;
selecting time domain coding based on
a coding bit rate to be used for coding the digital signal is less than a first bit rate limit; and
detecting that the digital signal comprises a short pitch signal for which the pitch lag is shorter than a pitch lag limit, wherein the pitch lag limit is a minimum allowable pitch for a Code Excited Linear Prediction Technique (CELP) algorithm for coding the digital signal.
7. The encoder of claim 6 , wherein the minimum allowable pitch is 34 when a sampling rate is 12.8 kHz.
8. The encoder of claim 6 , wherein the first bit rate limit is 24.4 kbps.
9. The encoder of claim 6 , the processor are further configured to perform the steps of:
selecting frequency domain coding for coding the digital signal based on:
detecting the digital signal comprises the short pitch signal,
coding bit rate is intermediate between the first bit rate limit and a second bit rate limit, and
a voicing periodicity is low.
10. The encoder of claim 6 , wherein, detecting the digital signal comprises a short pitch signal comprises:
detecting the digital signal comprises the short pitch signal based on a parameter for detecting lack of very low frequency energy or a parameter for spectral sharpness.