0dbfs Sine Wave measurement in DP shows +6dB in mixer??

[Timeline]

Has someone finally admitted here that +18 db is the clip point in MOTU IO's

Admit what? That's the spec of the unit (actually, to be precise, 18dbv is not the clip point. 18dbv is the ceiling. Anything above 18dbv will clip the input). It's also the same spec for the Traveler, 828mkII, 2408mk3, 24i/o and HD192 interfaces. It's very easy to check on input and output. All you need is a test tone generator and an accurate analog VU meter.


Dave

Yes, I have a VTVM, no scope but i have just never seen a published spec on MOTU IO's.

Also, when bridging, OP level seem adequate but looking into into lower impedance loads, levels are pressed. My API 8200's load HD192's easily. A UA 2192 can perform with much better headroom and output by comparison.

I wonder why more expensive IO's have more headroom?

[buzzsmith]

Okay, I'm the first to admit that I'm much more of a musician / arranger / composer than a "technical" engineer, but I like to feel that I've had some success in all of these endeavors, but it never hurts to ask and then learn from those who know more than I...

So this may be a really sophomoric question, in advance of which, I beg your pardon!

When mixing, I always try to avoid the clip light on the Master Fader (generally set to zero)...sometimes I do see the clip lights turn red, but hear no audible "distortion"...having said that, my general procedure is to find the offending combination of tracks that are creating the clip(s) and gently reduce levels in that area. (could be just an aggressive kick drum happening at the exact same time that a vocal got hot)

Am I mixing wrong? Is it OK to let the master fader indicate a clip since I really have 6 db of headroom? Both the Trim plug and Inspector (which seem to report identical mix levels) also will indicate a clip if I exceed zero. (same as the master fader)

I'd like to get "hotter sounding" mixes sometimes, which I know are not purely level issues, but, bottom line, is it acceptable to render a mix to CD when there may be a few indicated clips within DP?

Thanks, in advance, for any clarification!

=buzz=

[Timeline]

Hey Buzzsmith,

Since Dave didn't jump in, here's my experience on that.

The clip light "indicator" represents the last bit available on the MOTU IO when using it as a reference for the output of an IO.

If the mix 'track' faders have no group faders inserted, the clip of each frack fader would represent the highest OP the IO can produce but not the actual distortion point of the IO. One more bit would actually be required but driving an IO to +18 is not really sonically pleasing and the OP can sounds stressed, harmonically strange. That's a whole topic in itself though.

That said, several track faders driving a mix buss or group can produce additive signals that easily distort the OP of an IO but not internally until 32bit flaot is trunked to a fixed BR. When you bounce, you fix the BR. Internally, unbounced, 32B float architecture will perform without distortion regardless of clip light indication as I understand it.

On the plug side of this, I have found some third party 'plugs' may sound distorted because they may conflict with the float methodology in DP and trunk the dynamic range to fixed. I find it most noticable especially when chaining plugs.

Admittedly, this is where I'm not really sure what's going on because there is no published MOTU spec or explanation that I'm aware of on the type of 32-bit float 'math methods' used and the effects between them. I would guess MOTU communicates with third party plug makers but some of these makers would rather adhere to other math methods used by other software like Nuendo or logic. I would like to understand these standards better, if any.

As far as levels, I would run everything around the '0' indicators of the last fader befor the OP and if you want more apparent level, use a limiter with L2 or peak clip and drive the sucker.

[Archer]

Thanks for posting all this info Magic Dave!

[buzzsmith]

Gary B...

Thanks for the insight!

=buzz=

[jflandau]

A very helpful topic... thanks, all. That answers one of my questions, as to why the signal that I thought was peaking at -2 was actually coming out at something much lower. I've discovered that putting a MW Compresser, say, across the master fader seems to give a more accurate (if not perfectly so) reading for "true" level if I look at the input level.

Unfortunately, I've got some complicated 24-bit, 48k mixes with loads of automation that I've made to the old, inaccurate norm which need to be mastered. Is there any way of boosting the levels in general without totally redoing the mix? I'm afraid there isn't, but, hey, I'm always willing to learn... How much quality would I be sacrificing mastering the low-ish level signal mixes?

[Kubi]

Assuming your mix isn't, like, -36dB or something ridiculously low like that, you can boost the levels just fine on the Master fader insert with a trim plug. Boost so that the mix peaks around -6 to -4 dB, mastering engineers usually like to have a little headroom.

[Christian]

Magic Dave -

Thanks for posting this information; very helpful!

[jflandau]

Mmmm, about -14, so I guess not so bad as that-- I'll try that, thanks!!

[Timeline]

I would love to see a time where MOTU places "theory of operation" data in the manual that describes the inter-working philosophy of the DP where most of what is discussed in this thread is published.

This was common with older companies like Ampex as was supplying schematics & specifications on hardware. Obviously, those days are long gone as users don't usually do repairs nor could with surface mount designs.

I just see no competitive reason why a complete theory explanation on these concepts should not be published for users. Especially on BR float methodology and gain structure.

It would help us allot I think.

Additionally, thanks Dave for jumping in.

[Christian]

I would agree with the 'schematics' comment by Timeline... Specifically, It would be helpful to understand how the summing process functions in DP.