Plot your signal path. The signal path of a DSP circuit begins at the input point. Depending on the type of signal you wish to process, the input point can be line-level or audio. Stereo systems, digital musical instruments and instrument amplifier line-out jacks send a line-level signal. Line-level signals are less powerful than audio signals. RCA jacks and 1/4-inch instrument jacks can both carry line-level signals. Audio signals, such as those sent from a guitar or microphone are more powerful. If you are processing an audio signal, the signal path must incorporate an analog to digital converter. You can plot a signal filter to sit in the signal path in between the input point and the analog to digital converter.
Select a sample rate for your digital hardware data converter. The value for this component is set in Hz. For example, in a digital delay unit where a signal is passed through a 300-tap filter and is subjected to a sample rate of 48kHz, the minimum delay time yielded is 3.123 milliseconds.
Select a chip speed. The data memory, signal memory and compute engine components of a DSP circuit are stored in chips, which are integrated into the circuit. The speed of the chip determines the speed and clarify of processing. Low chip speeds can cause signal latency. This is a phenomenon whereby the time it takes for a signal to be processed is noticeably too long. A real world example of this is when a keyboard is routed through a DSP unit with low chip speed. You hit a note and there is an audible gap in between striking the note and hearing the audio. Chips with higher speeds are more expensive.
Make a basic sketch of your circuit. Begin by drawing a basic outline of each component you wish to incorporate into your DSP circuit. There are five main components to a DSP circuit: Input, program memory, data memory, compute engine and output. The program memory stores the data that is used to process the signal. The data memory stores the information to be processed, chiefly the audio or line-level signal. The compute engine performs the processing. The output sends the digitally processed signal outbound to an external application such as mix console.