Encoding and decoding speech signals

A method of processing an audio signal, the method comprising:

• receiving the audio signal over a communication channel;
• decoding the audio signal with a decoder using a first sampling rate;
• and
• filtering the audio signal using a first cut off frequency, the first cut off frequency being chosen in dependence upon the first sampling rate, wherein the step of filtering is performed before the step of decoding,
• wherein the method further comprises:
• determining the presence of a condition in which the sampling rate of the decoder is to be switched to a second sampling rate at a switching time;
• and
• if the condition has been determined to be present, gradually changing the cut off frequency used in the filtering step from the first cut off frequency to a second cut off frequency, the second cut off frequency being chosen in dependence upon the second sampling rate, such that the audio bandwidth of the decoded and filtered audio signal changes gradually when the sampling rate is switched to the second sampling rate.

Apparatus for transmitting an audio signal over a communication channel, the apparatus comprising:

• an encoder for encoding the audio signal using a first sampling rate;
• filtering means for filtering the audio signal using a first cut off frequency, the first cut off frequency being chosen in dependence upon the first sampling rate, wherein the filtering means are configured to be utilized after the audio signal is encoded;
• transmission means for transmitting the encoded and filtered audio signal over the communication channel;
• and
• determining means for determining the presence of a condition in which the sampling rate of the encoder is to be switched to a second sampling rate at a switching time,
• wherein the apparatus is configured such that if the condition has been determined to be present, the cut off frequency used by the filtering means is gradually changed from the first cut off frequency to a second cut off frequency, the second cut off frequency being chosen in dependence upon the second sampling rate, such that the audio bandwidth of the transmitted signal changes gradually when the sampling rate is switched to the second sampling rate.

Apparatus for processing an audio signal, the apparatus comprising:

• receiving means for receiving the audio signal over a communication channel;
• a decoder for decoding the audio signal using a first sampling rate;
• filtering means for filtering the audio signal using a first cut off frequency, the first cut off frequency being chosen in dependence upon the first sampling rate, wherein the filtering means are configured to be utilized before the audio signal is decoded;
• and
• determining means for determining the presence of a condition in which the sampling rate of the decoder is to be switched to a second sampling rate at a switching time,
• wherein the apparatus is configured such that if the condition has been determined to be present, the cut off frequency used by the filtering means is gradually changed from the first cut off frequency to a second cut off frequency, the second cut off frequency being chosen in dependence upon the second sampling rate, such that the audio bandwidth of the decoded and filtered audio signal changes gradually when the sampling rate is switched to the second sampling rate.