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Old 01-24-2008, 04:16 AM
Carl Kolchak Carl Kolchak is offline
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Default Mbox Mini - Operating Levels & I/O confusion, Anyone help?

Hi, I've re-posted this from a week or so ago elsewhere in the forum. I'm hoping this time it might get spotted by someone else with an Mbox mini who can say whether or not this is normal behavior.

Anyway, I've been trying out an Mbox mini and I'm finding the "Getting Started" manual to be woefully lacking in useful info.

When hooked up to calibrated monitors, running an old session the output level is reduced - O.K. the device seems to be outputting at the consumer -10db operating level (patching it into the desk seems to confirm this).

Why is the operating level not mentioned anywhere in the "Getting Started" manual?

Page 37 of the "Getting Started" Manual states:

"The Mon Out (Monitor Outputs) on the back of the
Mbox 2 Mini support 1/4-inch plugs. These connections
can be balanced or unbalanced TRS (Tip-Ring-
Sleeve) style connectors, or unbalanced connectors."

Which would infer that the outputs are balanced (and possibly running at the pro +4 operating level).

However, this is completely contradicted on the specifications tab of the Mbox mini Product Page , stating that both the Monitor outputs and the Line/DI inputs are unbalanced (and logically one could deduce at the consumer -10db operating level).

A quick glance at the back of the unit reveals that all the 1/4-inch connectors are of the T/R/S/ variety - though not necessarily fully wired.

Re. input levels:

I've yet to find a consumer device running at the -10db operating level that doesn't cause the signal to clip, even with the Mbox gain controls turned all the way down.

Cassette decks with a well recorded tape cause regular clipping, and forget about hooking up a CD player with any modern "Mastered to 0dBFS" material.

In DI mode, some monophonic synths just about get away with it, but hit a chord and it's full code. The same goes for Bass guitar.


I fed a 1k tone at -18dBFS (peak) out of the Right monitor out, in to a track monitoring input 1 (panned hard Left) expecting to receive a signal still at -18dBFS.

The signal registered as :

Input 1 = -12.6dBFS

-32.5dBFS with -20dB Pad engaged

-15.1dBFS with -20dB Pad engaged and input gain dialed up to "Unity Gain" marker.


Input 2 = -12dBFS

-32dBFS with -20dB Pad engaged

-15.5dBFS with -20dB Pad engaged and input gain dialed up to "Unity Gain" marker.

Which leads me to guess that the pre-amps cannot be completely bypassed.


I also notice that on the specifications tab of the Mbox mini Product Page , though nowhere in the manual, it states:

"Input Impedance (pad off): Inputs are DI only"

So does that mean the pads need to be engaged all the time for line level signals regardless of operating level?


The other quirk is that the mix control, when dialed all the way to input (fully Left) sums any signal to Mono.

That's fair enough, as the Mini doesn't feature the mono switch that the bigger Mboxes have, and the mini seems to be more aimed at single source recordings. You can always dial the mix control over to PT (fully Right) and set a lower buffer if your need to monitor in stereo.

I was just a little surprised that there is no mention of this.


So, any other Mini users - I'd be interested to hear your thoughts. I've seen other posts relating to low level output, and one regarding overcooked input sensitivity after a firmware update, so it appears I'm not alone here.


And Digi Admin.....

Please pipe up and set me straight on these issues (and revise the Manual for future releases).

1. What is the operating level supposed to be?

2. Are the I/O Balanced or Unbalanced?

3. Are the -20dB Pads supposed to be engaged for all Line level duties, and off for DI?

4. Are those marks on the front panel pre-amp dials supposed to represent unity gain?



Somewhat confused, though otherwise happy with the unit as a more flexible "Mbox Micro" mobile editing setup.

Cheers!
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