7.7.5.3 Sampling Frequencies and Oversampling
The ASRC converts an input audio stream with a sampling frequency defined either internally or externally to an audio stream at a configurable output sampling frequency generated either internally or externally.
Internal input or output sampling frequency is generated by a programmable division of GCLK. The division for input sampling frequency is defined in ASRC_MRx.INRATIO; the division for output sampling frequency is defined in ASRC_MRx.OUTRATIO.
The selection of the external trigger event for the input sampling frequency is made by configuring ASRC_TRIG.TRIGSELINx; the selection of the external trigger event for the output sampling frequency is made by configuring ASRC_TRIG.TRIGSELOUTx
If the input and output ratio are integer multiples, the ASRC behaves as a “synchronous” sample rate conversion.
The ASRC oversamples the incoming signal and then decimates the oversampled signal at the output sampling rate. The total oversampling ratio of the ASRC is 32768.
The input and output audio frequencies do not need to be synchronous.
Input and output sampling rates are defined by a division of the GCLK or by one of the signals in the table below.
| Trigger Index | Trigger Name |
|---|---|
| 0 | Internal trigger, a configurable division of GCLK |
| 1 | I2SMCC0 |
| 2 | I2SMCC1 |
| 3 | PDMC0 |
| 4 | PDMC1 |
| 5 | SSC0 RX |
| 6 | SSC0 TX |
| 7 | SSC1 RX |
| 8 | SSC1 TX |
| 9 | SPDIFTX |
| 10 | SPDIFRX |
| 11 | – |
| 12 | – |
| 13 | – |
| 14 | – |
| 15 | – |