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General Information
Audio Weaver is able to process signals at different sampling rates all within the same layout. This was seen with control signals but the feature is much more powerful. Audio Weaver is able to handle multirate processing in two different ways:
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In single block time processing all of the audio modules execute within a single thread at the same rate. In multiple block time processing there are multiple threads on the target processors and different block times execute within separate interrupt levels. Each approach is described in turn.
Single Block Time Processing
A module has an associated block size and sampling rate. We’ve been treating these wire properties as separate information but when combined they yield the block time, also referred to as block rate, of a module. For example, consider the system shown below.
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The Rebuffer module is useful for frequency domain processing when it is necessary to have a certain amount of overlap between blocks. The inverse of the Rebuffer module is the BlockExtract module. This module extracts a subset of samples and reduces the block size.
Multiple Block Time Processing
In some applications processing needs to be performed at multiple block times. Consider a system that has low latency processing with a block size of 32 samples combined with frequency domain processing at a block size of 256 samples. At a 48 kHz sampling rate, the 32 sample processing would occur every 2/3 millisecond while the 256 sample processing would occur every 5 1/3 millisecond. In Audio Weaver, this ratio of block rates is called the clockDivider. In the example above, the clockDivider would be 1 for the 32 sample processing, and 8 for the 256 sample processing.
Note: even though it’s a single AWD layout that can have multiple clockDividers, behind the scenes there is a distinct sublayout created for all the processing for each unique clockDivider.
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Here, the all the highlighted modules are processing at the 1/8th block rate. To achieve this system, the clockDivider field of the Sine1 module must be set to ‘8A’ in the Build tab of the Module Properties menu. All the modules downstream of the Sine1 module will then inherit this clockDivider and run at that same block rate.
Multithread Processing
Some systems are able to run multiple threads or processes in parallel. For example, a quad-core Cortex A target may be able to assign individual threads to execute on different CPU’s, allowing them to be processed concurrently. In systems that can support this type of processing (see the AWE Core OS product), the Buffer Up V2 and Buffer Down V2 modules can be used to create new sublayouts without having to change the block rate of the processing.
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Similar to multirate processing, all source modules can also be configured to run on a specific LayoutSubID by modifying the clockDivider property on the Build tab of the Module Properties menu.
Limitations
One feature of Audio Weaver is that the smallest possible block time in the system corresponds to the fundamental block size of the target system. This means that the smallest block time in the layout occurs at the input pin of the system. Audio Weaver buffers can only BufferUp to larger block times from the input block rate. When using a platform with a fundamental block size of 32 samples, it is not possible, for example, to BufferDown to a 1 sample block size for stream processing.
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