Speech enhancement with gain limitations based on speech activity

A method for enhancing a signal for use in speech processing, the signal being divided into data frames and representing background noise information and periods of articulated speech information, the method comprising the steps of:

• making a determination whether the signal of a data frame represents articulated speech information;
• determining a gain value and wherein, for a given data frame, the lower limit for gain values is a function of a lower limit for an a priori signal to noise ratio, the lower limit for the a priori signal to noise ratio for the data frame determined with use of a first order recursive filter which combines a lower limit for an a priori signal to noise ratio determined for a previous data frame and a preliminary lower limit for the a priori signal to noise ratio of the data frame;
• and
• applying the gain value to the signal, wherein a lower limit for gain values applied for a data frame determined to represent articulated speech is lower than a lower limit for gain values applied for a data frame determined to represent background noise only.

A method of encoding a speech signal, the speech signal representing background noise and periods of articulated speech, the speech signal being divided into a plurality of data frames, the method comprising the steps of:

• applying a transform to the speech signal of a data frame to generate a plurality of sub-band speech signals;
• making a determination whether the speech signal corresponding to the data frame represents articulated speech;
• applying individual gain values to individual sub-band speech signals, wherein a lower limit for gain values applied for a data frame determined to represent articulated speech is lower than a lower limit for gain values applied for a data frame determined to represent background noise only;
• applying an inverse transform to the plurality of sub-band speech signals to produce a data frame of an enhanced speech signal;
• multiplying a less current portion of a data frame of the enhanced speech signal with a synthesis window to produce a multiplied less current portion of the data frame;
• multiplying a more current portion of the data frame of the enhanced speech signal with an inverse analysis window to produce a multiplied more current portion of the data frame;
• adding the multiplied less current portion of the data frame to a multiplied more current portion of a previous data frame of the enhanced speech signal to produce a resulting data frame for use in speech compression;
• and
• applying a speech compression process to resulting data frames of the enhanced speech signal.

A method for enhancing a signal for use in speech processing, the signal being divided into data frames and representing background noise information and periods of articulated speech information, the method comprising the steps of:

• making a determination whether the signal of a data frame represents articulated speech information;
• determining a gain value, wherein the gain value is limited to be no lower than
• a first limit value, when the data frame is determined to represent
• articulated speech, and
• a second limit value, when the data frame is determined to represent background noise only,
• wherein the first value is lower than the second value, wherein each of the limit values is a function of a limited a priori signal to noise ratio, and wherein the limited a priori signal to noise ratio for a data frame is determined with use of a first order recursive filter which combines a limited a priori signal to noise ratio determined for a previous data frame and a preliminary lower limit for the a priori signal to noise ratio of the data frame;
• and
• applying the gain value to the signal.