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Old 11-09-2010, 11:26 AM   #51
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Join Date: Aug 2006
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Originally Posted by Fabian View Post
...could someone please explain what the "Maximum Input Level" and output levels below really mean in relation to Reapers metering? Thanks.

Microphone Inputs	(2) Female XLR Pin 2 Hot
Input Impedance		600 ohms balanced
Phantom Power		+48 Volt
GAIN			+44 dBu
EIN			-115dB A-weighted @44dB gain (150 Ohm source impedance)
Maximum Input Level	+6.5dBu
Excellent post.

dBu is typically calibrated so that 0dBu equals -18dBFS on a digital meter.

That means that +6.5dBu is equivalent to about -11.5dBFS on a digital meter.

IOW, your interface is designed to operate within spec at up to -11.5dB on REAPER's input meters.(see note*)

So what does that really mean for your studio practice? Who knows. The manufacturer is telling you that the device is meant to perform within spec at levels up to around -11.5dBFS. Beyond that, it doesn't say. Maybe it will hard-clip everything. More likely, it will handle short peaks and transients just fine with a slight worsening of THD performance that becomes more egregious the more sustained the signal above threshold is. Performance losses may be somewhat frequency- or dynamics-dependent above threshold.

The point of the post that spawned this thread was not to tell you good or bad, just to suggest that you can side-step all this stuff by simply recording at lower levels. Alternately, everyone can post all their specs and argue over whether which levels should be good enough and we can all speculate about what probably happens above that 6.5dBu threshold...

*Note, AGAIN, that analog calibration is not an exact science, and there are sometimes slight differences between American and European definitions, etc. So, AGAIN, we're talking about blurry areas, not bright-line definitions. Which is exactly the problem, that all the digital literature and discussion ignores the messier realities of analog input and output stages, and "analog"-sounding plugins and processors, and also the potential undetected problems of inter-sample clipping caused by digital processing such as steep filters etc. Not to mention the generally iffy quality of digital peak detection.

EDIT: BTW, the really telling one on your spec above is the +13bDu max LINE INPUT level. That means, that even using an outboard preamp and feeding signal "straight to the converters", the interface is STILL only spec'd to handle up to -5dBFS or so, which is EXACTLY what I've been getting at. Even if you fed a signal straight into that interface with no gain, and your meters showed no clipping, the input stage itself is distorting above -5dBFS. Note also that even the output stage shows a max line level of +16dBu (-2dBFS). So, again, you have distortion even if the digital meters show zero clipping. There's no such thing as all-digital!!!

Last edited by yep; 11-09-2010 at 11:33 AM.
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