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7. Level issues

7.4 Clip level mismatch

If analogue devices are used before or after a networked audio system’s analogue inputs and outputs, such as external analogue pre-amplifiers or power amplifiers, then the corresponding terminals must be connected. If the clip levels of these terminals don’t match, the level difference can reduce the system’s dynamic range (in other words: waste it). As most analogue devices use buffer amp circuits to provide inputs and outputs that are independent of the connected terminal’s impedance, clip levels are a fixed value - they can not be changed by the system designer or sound engineer without opening the device cabinet to perform a hardware modification.

To illustrate how clip level mismatches cause the dynamic range to be decreased, figure 706 a, b and c present the connection of the analogue input of three different power amplifiers to a Yamaha DME24N analogue output, with different clip levels of the power amplifiers input as listed in table 701.

table 701: clip levels of the Yamaha DME24N and three different power amplifiers

device terminal clip level
Yamaha DME24N output +24 dBu
power amplifier P1 input +24 dBu
power amplifier P2 input +27 dBu
power amplifier P3 input +21 dBu

Clip level mismatches cause a system’s dynamic range to be limited by as much as several dB’s - raising the system’s noise floor by several dB’s. Specially for systems with high power loudspeakers this can be a problem - as the noise floor below 100dBFS becomes audible for the audience situated close to the speakers. If the mismatch causes a clipping risk - as in figure 706c where the power amplifier clip level is lower than the system output’s clip level - the system designer or sound engineer has to manually limit the system’s output level in the digital domain.

In every networked audio system design, it is advised to check the clip level specifications at every line input (eg. wireless receivers) and output (eg. power amplifiers) of the system to know if any digital gain should be designed into the DSP processes to prevent mismatch clipping. Some devices offer internal DIP switches or jumpers with a choice of multiple clipping values. For high power high quality applications, it might be worth while to consider an external passive analogue attenuator if an internal option is not available.

>>7.5 Double A/D-D/A pass signal paths

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