While measuring the Motu M2 in loopback, I inadvertently used a TS-XLR cable on the M2 input.
The connection was TRS -> XLR -> TS.
TS connectors have only 2 contacts, one among them being the sleeve. They are the equivalent of an RCA connector with different mechanical interface.
TRS have 3 contacts. They are the equivalent of an XLR connector with different mechanical interface.
Basically I was connecting the balanced output to an unbalanced input, shorting the 'cold' wire to ground.
While it's accepted to connect unbalanced to balanced, the reverse is not a good idea.
- first it's shorting one output to ground, never a good idea, even if properly designed hardware should survive this.
- second its distorting the signal. A lot. in the case of the Motu M2, harmonic 2 goes from -120 dB to -90 dB, harmonic 3 from -108 dB to -80 dB, ...
Since a picture always explains more than a lot of text, here you are:
The connection was TRS -> XLR -> TS.
TS connectors have only 2 contacts, one among them being the sleeve. They are the equivalent of an RCA connector with different mechanical interface.
TRS have 3 contacts. They are the equivalent of an XLR connector with different mechanical interface.
Basically I was connecting the balanced output to an unbalanced input, shorting the 'cold' wire to ground.
While it's accepted to connect unbalanced to balanced, the reverse is not a good idea.
- first it's shorting one output to ground, never a good idea, even if properly designed hardware should survive this.
- second its distorting the signal. A lot. in the case of the Motu M2, harmonic 2 goes from -120 dB to -90 dB, harmonic 3 from -108 dB to -80 dB, ...
Since a picture always explains more than a lot of text, here you are: