Computationally efficient data rate mismatch compensation for telephony clocks

An apparatus for matching a first audio signal sample rate of a first audio signal, to a second audio signal sample rate of a second audio signal, the first and second audio signal sample rates being different from each other, the apparatus comprising:

• a determiner, configured to determine whether the first signal sample rate is greater than or less than the second signal sample rate;
• a duplicator coupled to the determiner and configured to create copies of a first frame of samples of the first audio signal;
• a window function generator, configured to generate a gradually increasing window function;
• a divider coupled to the window function generator and configured to generate a gradually decreasing window function;
• a first multiplier coupled to the window function generator and to the duplicator, the first multiplier configured to multiply a first copy of the frame of samples of the first audio signal by the gradually increasing window function to provide a first windowed frame;
• a second multiplier coupled to the divider and to the duplicator, the second multiplier configured to multiply a second copy of the frame of samples of the first audio signal by the gradually decreasing window function to provide a second windowed frame;
• and,
• a sample subtractor/generator, configured to add and remove a first sample from the first windowed frame and add and remove a last sample from the second windowed frame;
• and
• a frame adder, configured to combine signals output from the sample subtractor/generator.

An apparatus for matching a first audio signal sample rate of a first audio signal, to a second audio signal sample rate of a second audio signal, the first and second audio signal sample rates being different from each other, the apparatus comprising:

• first and second communications devices, the first and second communications device generating first and second audio signal samples having the corresponding first and second signal sample rates;
• a processor coupled to the first and second communications devices;
• and
• a memory device coupled to the processor by a bus, the memory device storing executable instructions for the processor which when executed cause the processor to:
• determine whether the first signal sample rate is greater than or less than the second signal sample rate;
• if signal sample rates are different, create copies of a first frame of samples of the first audio signal the executable instructions causing the processor to then:
• multiply a first copy of the frame of samples of the first audio signal by a first gradually increasing window function to provide a first windowed frame;
• multiply a second copy of the frame of samples of the first audio signal by a second gradually decreasing window function to provide a second windowed frame;
• if the first signal sample rate was determined to be greater than the second signal sample rate, the executable instructions causing the processor to:
• (1) remove a first sample from the first windowed frame;
• (2) remove a last sample from the second windowed frame;
• and
• (3) sum the first and second windowed frames to create a reduced-sample frame;
• if the first signal sample rate was determined to be less than the second signal sample rate, the executable instructions causing the processor to:
• (1) add a new first sample to the first windowed frame;
• (2) add a new last sample to the second windowed frame;
• (3) add the first and second windowed frames to each other to create an increased-sample frame;
• and;
• transmit either the reduced-sample frame or the increased-sample frame to a communications device configured to create an audible audio signal from audio signal samples.