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6. Distribution & DSP issues

6.2 Interconnected DSP distribution

DSP MAC operations are performed at a bit depth higher than the 24 bit sampling bit depth to keep the accumulated quantization noise of rounding errors - generated with every MAC operation - below 24-bits. As most systems utilize multiple DSP chips, most DSP manufacturers support internal audio connections between DSP chips at a bit depth of 32 bits or more - reserving 8 or more bits for headroom and quantization noise to preserve a minimum resolution of 24 bits. If there is only one DSP device in the system, 24-bits are enough to connect to A/D converters and A/D converters in the system without loss of resolution.

If multiple DSP devices have to be connected in a system using external digital audio formats, 24-bit formats can be used, but this will increase the system’s quantization noise above the 24-bit LSB level of -144dB. This is not a big problem if the signal path crosses such a connection only once - for example to connect to a digital speaker processor or a digital effect. But if a signal path uses the connection multiple times - for example in cascaded mixing consoles or in distributed free configuration DSP systems, the quantization noise might increase towards audible levels (above -120dBFS, inside the audio universe dynamic range as presented in chapter 4.2). To support high resolution interconnection of devices, some devices offer 32-bit interconnection, such as the CL and Rio series supporting Dante 32-bit mode(*6A).

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