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miniDSP Low cost, modular Digital Signal Processor (DSP) kits for the DIYer from miniDSP.

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Old 30th November 2012, 12:08 AM   #1
DrNick is offline DrNick  United Kingdom
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Location: Glossop
Default Signal levels shown in MiniDSP software look too low - is it working?

I have been putting together a sub using a minidsp and a BK electrics amp. I've had hissing problems so I decided to measure the voltages everywhere, feeding sine waves generated by my PC through a digital input to my main amp, an Arcam AVR300, and then taking the lfe channel output to the minidsp. I directly measured the voltages at the input and output of the minidsp with a multimeter. I found that the voltages on the output of the miniDSP match very closely to those of the input, *but* the displayed level shown in the software looks way off. I have posted a spreadsheet of the measurements here.

If a 537 mV input signal shows up as -16.9 dB, this implies that the reference potential that would give zero dB, the maximum input, would be 3.7 V. I'm using the equation below to work this out, where V is the input signal 0.537 V, Lv is the signal level in dB, and V0 is the calculated reference voltage level. If anyone can see why this might be wrong, I'd be very grateful?

Click the image to open in full size.

I'm a bit worried that my unit is faulty, so if anyone has data they can compare to, please shout! I have the unit set to the 0.9V sensitivity for these measurements.
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Old 9th December 2012, 12:23 AM   #2
Davey is online now Davey  United States
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Location: Bremerton, WA.
Your unit is not faulty. The meters on the plugins indicate with a 3db (RMS) discrepancy. Full scale inputs and outputs near the 0.9 VRMS level will indicate -6db on the meters.
If your meters are indicating higher levels than that, you're clipping.

Cheers,

Dave.
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Old 10th December 2012, 08:12 AM   #3
DrNick is offline DrNick  United Kingdom
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That is good to know, thanks!
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