Asynchronous Sample Rate Converter vs. regular SRC

A "regular" sample rate converter is synchronous and converts between two fixed sample rates.  For example, converting from 8 kHz to 32 kHz.  Synchronous conversion is most efficient when the rates are related by small integers.  Going from 8 to 32 kHz is a fixed increase of 4x.  Converting an audio file from 44.1 kHz to a fixed output rate of 48 kHz can be accomplished using synchronous conversion but the factors aren't that nice any more.  You need a ratio of 160/147.

There are many applications where you have multiple independent clocks in the system and need to convert everything to a fixed rate.  Consider a USB audio device that receives data from the PC and then converts it to analog.  The PC is sending audio based on its own clock rate while the D/A converter in the USB device has a separate clock.  These clocks are distinct and slowly vary over time.  For this application, you need an asynchronous sample rate converter.  Asynchronous converters can handle slowly varying clocks rates.  (The USB spec provides for several different ways to synchronous clocks. Using a sample rate converter is just one way of doing it.  There are other methods that don't require an asynchronous sample rate converter.)  Mixing independent digital inputs each with their own clock also requires an asynchronous sample rate converter.  Even if both inputs are nominally at 44.1 kHz, since they have separately clocks they won't both be at exactly the same rate.  One may be at 44100 while the other at 44100.02.

Getting back to converting from 44.1 to 48 kHz, this is actually easier using an asynchronous sample rate converter.  The ratio of 160/147 is no problem.

DSP Concepts has an asynchronous sample rate converter optimized for the Cortex-M3 and -M4 processors.  The converter is optimized for audio applications and has extremely low distortion and noise components.  All processing is done with at least 32-bits of precision.

A "regular" sample rate converter is synchronous and converts between two fixed sample rates.  For example, converting from 8 kHz to 32 kHz.  Synchronous conversion is most efficient when the rates are related by small integers.  Going from 8 to 32 kHz is a fixed increase of 4x.  Converting an audio file from 44.1 kHz to a fixed output rate of 48 kHz can be accomplished using synchronous conversion but the factors aren't that nice any more.  You need a ratio of 160/147.

There are many applications where you have multiple independent clocks in the system and need to convert everything to a fixed rate.  Consider a USB audio device that receives data from the PC and then converts it to analog.  The PC is sending audio based on its own clock rate while the D/A converter in the USB device has a separate clock.  These clocks are distinct and slowly vary over time.  For this application, you need an asynchronous sample rate converter.  Asynchronous converters can handle slowly varying clocks rates.  (The USB spec provides for several different ways to synchronous clocks. Using a sample rate converter is just one way of doing it.  There are other methods that don't require an asynchronous sample rate converter.)  Mixing independent digital inputs each with their own clock also requires an asynchronous sample rate converter.  Even if both inputs are nominally at 44.1 kHz, since they have separately clocks they won't both be at exactly the same rate.  One may be at 44100 while the other at 44100.02.

Getting back to converting from 44.1 to 48 kHz, this is actually easier using an asynchronous sample rate converter.  The ratio of 160/147 is no problem.

DSP Concepts has an asynchronous sample rate converter optimized for the Cortex-M3 and -M4 processors.  The converter is optimized for audio applications and has extremely low distortion and noise components.  All processing is done with at least 32-bits of precision.