MOTU 828 mk3's DAC : 0 dBfs = how many dBu / dBV?

[bejj]

Hi
(I didn't find the answer in the MOTU specifications).

When playing a sine wave at 0 dBfs (full scale) to the XLR main output, which voltage (RMS) does it give? i.e. which dBu or dBV level does it give (NB: 0 dBV = 1.0 Vrms)

Of course this depends of the internal DAC (digital to analog converter) inside the MOTU.

Does one of you have this info?

Thanks!

[mikehalloran]

You can never match dBFS and dBu.

http://www.sengpielaudio.com/calculator ... al%20level.

[bejj]

You can never match dBFS and dBu.

Let's do this experiment:

• I play a 24-bit 96 Khz WAV file that is a 1Khz sinusoid peaking at 0 dBfs on the output of my MOTU 828 mk3. This is possible, is that right?
• Then the DAC (Digital to Analog converter) of the MOTU will convert this signal to an audio analog signal.
• We can measure this analog signal with an oscilloscope:
  
  
• This analog signal is a sinusoid, it has a peak voltage, let's say it is 0.500 V peak, i.e. a RMS of 0.354 V (there is a ratio of sqrt(2) between peak and RMS for a sine wave)
• Then we can convert this to dBV: dBV = 20*log10(0.354 / 1.00) = -9.02 dBV

So it is 100% technically possible to analyse what a 0 dBfs sine wave (digital) will produce when it will be converted to an analog signal after the DAC.

Has anyone done this measurement?