I've always wondered about this.

My Microphone (Audio Technica 4033) has a 0db/-10 db switch on the back.

My ART Tube Pre-amp (which I put before the MOTU and after the Mic) has a +20db switch on the input.

My MOTU 828mkII Audio Interface has trim pots for the two mic/guitar inputs which have their own preamps, and the other 8 inputs on the back don't have trim pots, because they don't have preamps.

All of the motu's inputs can be +4/-10 switched.

Exactly how should I set this up levels wise?

d

This post has been edited by Dominic Betmead: Tue 8 Feb 2005, 12:28

The -10dB PAD switch on the AT4033 is used when the mic is placed in front of very loud sounds, say as overheads for drum miking. When recording vocals or acoustic guitar etc it is better to leave it on normal.
The tube preamp will have some sort of adjustable input gain, usually between 50 to 70dB of amplification for microphone inputs. This gain is used to get the mic signal up to line level (the level of the MOTU audio interface). The setting for the gain will depend on how loud the sound source and how sensitive the mic is. You will need to use either the meters on the preamp or within your sequencer/audio recorder to set this.
i assume the +20dB switch on the preamp is additional gain for especially weak sound sources or, more likely, it is only applied to instrument inputs to bring them up to line level.
On the MOTU you would plug the outputs of the ART into standard line inputs, not a mic or instrument in, and set this to the same setting as the ART (either -10 or +4, you will need to look it up in the ART manual).
+4 and -10 are different line level specifications. +4 is used in professional environments, -10 is semi-professional. As long as your gear is set to the same it doesn't matter either way. The only problem is when you go out of a +4 into a -10. This can lead to overloading and distortion.
Hope this helps

That's great thankyou.

I think i see now. A +4 output is boosted, but a +4 input is attenuated.

Kind of. It definitely seems that way when you hook it up to a -10 source or destination. Just an additional note to clarify this: +4 is equivalent to 1.228 Volts. Whenever a signal of this strength is input into a device set to +4, it will display 0 on the meters. -10 is equivalent to 0.316 Volts. In a device set to -10 this voltage will display 0 on the meters. It is really that simple, the confusion sets in when the two are mixed. So bottomline: try and keep all devices matched.
Hope this clarifies it. The whole thing is rather technical, but it pays to get your head around it. (Oh no, I am lecturing again...)
Kwasi