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How Does the Volume Control of the miniDSP 2x4 Affect the Output Clipping Level 8 months 2 weeks ago #64875

  • joegorin
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I am configuring two systems with miniDSP 2x4 to allow use of the volume control. I do not understand how it will affect the noise level and the system clipping level.

Hypothesis 1, "Multiplying DAC": The 0 - 5 V level applied to the volume control pin acts to change the analog gain of the output DAC. This is commonly called a "multiplying DAC." All DACs act to multiply the digital input word by the reference voltage. In a multiplying DAC, the DAC still works well with a very wide range of reference voltages. In this hypothesis, the analog signal at the volume control is quantized to 8 bits, as evidence shows it is, then applied to an 8-b DAC, which is then used as the reference for the output DAC. In this hypothesis, it is likely that reducing the volume control setting reduces the output noise of the DAC, which is highly desirable to keep it from being significant with lower volume settings. But the maximum output level declines. My example would be common: The power amplifier clips around 0.9 Vrms, as does the miniDSP output DAC when the gain is set to maximum, but setting the volume control lower reduces the available power from the power amplifier. This is highly undesirable, and wasteful of the most expensive part of mos audio systems, the available amplifier power. Imagine program material that is, at its maximum, -6 dB compared to the input ADC clipping level. Assume the miniDSP programming has 10 dB net gain at some frequencies. When the volume control is set to the desired level, the DAC clips at a much lower level than the power amplifier.

Hypothesis 2, "Digital Multiply." In this hypothesis, the A/D converted volume control level is applied to a multiplier in front of the DAC. As in Hypothesis 1, noise from the input ADC is attenuated when the volume control is reduced, but the clipping level is not reduced for signals of adequate level, and the output DAC noise, specified as -98 dB below full scale, is not affected.

Is the behavior one of these two possibilities? Which one?

I have searched thoroughly and not found the answer in this forum. Thanks in advance.

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