There are two types of memory used when allocating memory for audio objects.
- Scratch Memory: Scratch memory is non persistent memory that is used by an audio object only during an audio interrupt. Data in the scratch memory is not guaranteed to remain unchanged from one audio interrupt to the next. Up to and including Deep Purple, each object is restricted to one memory record. Developers can determine the size, alignment and latency level required.
- Coefficient Memory: Coefficient memory is any other type of persistent memory that is required by the audio object. There is no limit to the number of records developers can create. Developers can configure the size, alignment and latency levels required for each record and they can be different for every record.
Audio Buffers: The audio buffers provided in the calc function are intended to be read and write only, i.e. they should not be used for intermediate calculations. If intermediate buffers are required, scratch memory must be requested. The reason for this is that it is not guaranteed that the buffer per channel will be unique for unconnected pins. For unconnected pins on the input side, xAF provides a single buffer (filled with zeros) that is shared by all audio objects in an xAF instance. It is expensive (MIPS-wise) to clear this buffer each time, so it is important not to write data to this buffer and leave it untouched, as it will be read by all audio objects with unconnected pins. For unconnected output pins, xAF allocates a single “dummy” buffer for all unconnected pins, rather than a unique buffer per channel.
For audio objects that support in-place processing and all pins are connected, xAF will assign the same input and output buffer per channel, but if there are unconnected pins, the input and output buffers will be different, so the audio object developer should not blindly rely on the input and output buffers being the same or different. It is highly recommended to implement proper checks if the algorithm requires any of the above input/output buffer constellations.