DSP Library
Philosophy
Tiliqua’s DSP library is designed as a suite of DSP components - independent ‘cores’ which can be connected together in different ways in order to build a custom DSP pipeline. It makes heavy use of Amaranth streams (lib.stream) for connecting components and lib.fixed for fixed-point types. lib.stream makes it possible to chain DSP components together in different ways (without components needing to know implementation details of each other), and lib.fixed makes it easier to write common numeric operations in Amaranth.
Note
Streams are an Amaranth construct describing a stream of data that is accompanied by a valid/ready handshake. This is a simple protocol used commonly in digital logic. For more details, see Data streams in the Amaranth documentation.
Interconnect
Building a custom DSP pipeline with the components provided here is often an act of figuring out how to massage the input and output ports of each component such that the design does what you want. In simple cases, like oscillators or filters, DSP components will often have a self.i stream for incoming and self.o stream for outgoing samples - these can be chained together in any order using wiring.connect(). In more complex cases, like delay lines, components may expose a memory bus (for writes to external memory), multiple input or output ports, or global registers. It is important to read the documentation of each component and take a look at some of the example cores in order to understand how each component can be used, and how exactly input and output samples are synchronized.
As of now, input and output ports of DSP components generally take on one of the following shapes:
stream.Signature(fixed.SQ): A stream of audio samples, one at a time.
stream.Signature(ArrayLayout(N, fixed.SQ)): A stream of N audio samples, one 1D array at a time. This is used for multi-channel, time-synchronized inputs and outputs – like Tiliqua’s 4 inputs or 4 outputs, or thetiliqua.dsp.MatrixMixcomponent. These can be split into streams of single samples usingtiliqua.dsp.Splitortiliqua.dsp.Merge(see Stream utilities).
stream.Signature(StructLayout({...})): A stream of N different types of data, one set at a time. This is often used when each audio sample needs a piece of metadata alongside it (e.g. realtime tweakable filters liketiliqua.dsp.SVF).
stream.Signature(Block(...)): Some components can only operate on blocks of samples, liketiliqua.dsp.fft.FFT- see Block-based Processing for details.
The art is in knowing exactly which components can be used in translating between the interface styles. For example, tiliqua.dsp.fft.ComputeOverlappingBlocks can help going from a sample stream to a block stream. tiliqua.dsp.Split for going from an ArrayLayout to independent sample streams. Depending on the application, often StructLayout streams will need some manual handshaking logic. There is no one right answer for every adaptation, especially in cases where you have some control signals alongside synchronized audio streams.
A few components have auxiliary interfaces to the outside world. Examples are tiliqua.dsp.DelayLine, which may have a bus port to talk to external memory (for storing audio samples), or usb_audio components which require a connection to a USB PHY to service their audio in/out streams.
‘Basic’ and ‘Specialized’ components
DSP cores are split into 2 types, ‘Basic’ and ‘Specialized’. Basic cores do not require qualified access - after a statement like from tiliqua import dsp, these can be accessed through dsp.Split or similar. ‘Specialized’ cores need qualified access and may be accessed through dsp.fft.STFTProcessor or similar.