Signal flow¶
This figure illustrates the conceptual signal flow through the miniDSP ADept, assuming it's being used with phono input:
The signal flow is divided in two: analog and digital. The first stage is an analog gain stage, where relay-switched resistors alter the gain of the signal from the cartridge. The amplified signal is then converted to digital form in the analog-to-digital convertor (ADC).
After the ADC, the digital signal is digitally amplified and has the RIAA equalization curve applied to it. Having digital gain as well as analog gain provides the best overall performance – see Technical details for more information. Finally, the signal is converted from the internal representation to a 24-bit integer format for digital output.
Ideally, we want the audio signal to be as high as possible throughout the audio path without clipping. In the signal flow as shown above, there are two places where clipping can occur:
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In the ADC. If the amplified voltage from the cartridge is too high, the maximum voltage to the ADC will be reached and there will be higher distortion.
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In the digital output stage. The digital output signal is a 24-bit integer format (the same as SPDIF digital signals always are). If the signal is too high to "fit" then clipping is the result.
Between these two locations in the signal flow, there is a digital gain stage and the RIAA EQ. Because of this, it is possible for the digital output to clip even though the analog stage has not, and vice versa – it is frequency-dependent. The ADept provides the necessary means for the user to optimize its gain structure for the cartridge and (to a lesser extent) the records being played.
Info
Clipping in the ADC is not observed as a squaring-off of the waveform. To observe ADC clipping, it is necessary to use a known test signal and a spectrogram to observe the rise in harmonics above the point of clipping. For most users, using the front panel clipping LED is the simple way to monitor for ADC clipping.