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[Dinogi]

I was reading some downloaded manuals and noticed this on the specification page of one particular product.
The name or manufacturer doesn’t really matter, the device I refer to costs a good chunk of money, gets great reviews, and apparently does what it does very well.
I was just curious about an engineers take on why a designer/manufacturer would reference to dBm, instead of dBu or even dBV.
It’s a unit of measurement I have not previously run across in the dBu world I inhabit.
A quick wiki just said something about absolute power referenced to a milli-watt , but I couldn’t glean anything directly related to audio.
Dean 

[mbrebes]

It's an old standard from the days of transformers and terminating with 600 ohm resistors.  .775V into a 600 ohm resistor is 1 mW or 0dBm.  dBu is the scale that is referenced to .775V without the load restriction.  Hope that helps.

[Dinogi]

Now I feel stupid. I'd not thought about it from the old school telephone company 600-600 ohm perspective. So essentially although a bit archaic, dBm is still a valid unit that is interchangeable with dBu from a practical standpoint. At least as far as comparing specs. I now recall the u in dBu meaning unreferenced or unloaded. Am I getting this right??
My whole now moot, point actually was to poke fun at the quirky nature of design engineers. It reminded me of the Nagra recorders we used in filmmaking for several decades. The designer was unquestioningly brilliant but perhaps a bit mad. Used dual banana plugs for headphones instead of ¼ inch and if I remember correctly even reversed the gender of the xlr connections on some models. He was able to ignore standards because he designed what was arguably the finest device of its type ever built. By the way, the device I was referring to is the ATI 8MX2 mixer. I was looking for a small preamp/mixer that can cover multiple applications, and was surprised by the use of dBm in their specs.
Thanks
Dean

[John Roberts {JR}]

Now I feel stupid. I'd not thought about it from the old school telephone company 600-600 ohm perspective. So essentially although a bit archaic, dBm is still a valid unit that is interchangeable with dBu from a practical standpoint. At least as far as comparing specs. I now recall the u in dBu meaning unreferenced or unloaded. Am I getting this right??
My whole now moot, point actually was to poke fun at the quirky nature of design engineers. It reminded me of the Nagra recorders we used in filmmaking for several decades. The designer was unquestioningly brilliant but perhaps a bit mad. Used dual banana plugs for headphones instead of ¼ inch and if I remember correctly even reversed the gender of the xlr connections on some models. He was able to ignore standards because he designed what was arguably the finest device of its type ever built. By the way, the device I was referring to is the ATI 8MX2 mixer. I was looking for a small preamp/mixer that can cover multiple applications, and was surprised by the use of dBm in their specs.
Thanks
Dean

Technically 0 dBm, is 1 mWatt so only interchangeable with dBu for the single case of 600 ohm termination. This is archaic and too much info for modern consideration. In practice when people say 0 dBm the 600 ohm termination is implied or ignored and they generally mean the same voltage as 0 dBu.

JR