I guess we generally assume that “unity” means that voltage going in is the same as the voltage coming out, but who can say what these people are talking about. Apparently their website is lying about the max input on the rear panel inputs which then makes you wonder if any of those specs can be trusted. What’s the actual max input on the front panel ones or the mic inputs? What’s the maximum from the line outs. That also says +18dbu, but is actually also only +10?!?
Please reply to this person at Presonus and tell them for me that the should be ashamed of themselves for trying to pass of a unit with +10dbu max “line” input as anything other than a toy and that they should be flat out sued for actual misinformation on their spec sheet.
Just to be that guy, (since [MENTION=89697]ecc83[/MENTION] kinda went there) the idea of a “maximum rms” in this context is meaningless. The limit is the voltage rail and that is all about the actual instantaneous voltage at any given point, and has nothing to do with average level. With real world signals we can’t make any meaningful assumptions about the relationship between rms and p2p, so when talking about this kind of headroom limit, we really should talk in p2p, I think.
Err? No Ash'. I quoted voltages in rms because that is the way signal and other voltages are 'usually' specified. 'RMS' in in fact usually assumed and not given.
There has grown up a tendency in audio circles to quote "peak" signal levels and this is rather meaningless. The terms "peak" "average" "rms" "peak to peak" have precise meanings in electrical and electronic engineering but are bandied about willy-nilly in audio writings.
The term "rms" simply means that voltage that would produce the same heating effect in a resistor as DC. Thus our mains supply is nominally 230V rms but if you put 230V DC from batteries into your kettle it would make your cuppa just as quickly. The relationship between 'peak' and rms depends upon the waveform. For pure sine divide peak (or 1/2 pk-pk) by 1.414 but for a square wave the peak and rms value is identical. Other waveforms will have other relationships.
I will agree this is all a mess. For the representation of signals in a DAW we are only interested in the peak value, how close it comes to 0dBfs. Often it is said we should be recording at -18dBfs as an "AVERAGE" level but average in this context simply means "as our eye/brain" interprets the visual display over a short time period. The meters are still reading the peak of the signal (as the software computes it).
I also agree that signal levels are, in general limited by supply rails but not always! A 'pro' balanced output will use two amplifiers of opposite polarity and deliver twice the supply limited voltage (rms!) If the output comes from a transformer you can have just about any signal voltage you fancy!
A word is perhaps moot here about "true rms" digital test meters? They only read rms for power frequencies, up to 400Hz, 1kHz if you are lucky! Do not trust them to give an accurate reading for audio signals or noise.
They also have a VERY limited HF response. Most are 6dB down by 2kHz and some by 1kHz. Digital meters are superbly accurate, even the £20 ones and have a high input impedance and are in many ways the best things to come into electronics testing since bread-come-cut but, if you want to calibrate your Revox B77...FIRST calibrate your DMM!
(I see Mary Whitehouse lives on in the forum censor!)
Dave.