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Hello Mighty DP Brain Trust,
Setting up 5.1 surround mix and I noticed when I turn on the LFE 120Hz lowpass filter in the panner it flips the phase. Is there a reason it should do this for theatrical presentation? It causes a huge hole in the spectrum. Am I missing something or is this a bug?

Don

[sound of crickets]

Have you tried contacting MOTU since your post?

I just started a TechLink after my last look here.
I was hoping the brain trust had the answer.

Hello,
It gets worse, implementing eVerb or ProVerb on a 5.1 aux channel produces dubious results. For example eVerb will only accept audio on the Rs channel, all others are mute so no reverb created. Also there is no way to de-correlate the separate channel outputs. I'm on the hunt for some good 5.1 verb.

Don

dunno about your phase problem, never encountered that, sorry...

I think IRCAM (Flux) make a surround verb, as does Exponential audio, maybe Waves too?

Hello,
I have another question:
Is there a way to have the sends panning mirror or follow the main panning?

Don

Hello Again,
OK, so I've been running some tests. I have the proton VI playing a 49 Hz sine wave through a 5.1 panner. I recorded the output to check the phase. The LFE channel does indeed flip the phase 180* out when the LPF is turned on.
Another option is to leave it bypassed and insert an EQ with low pass filter on the LFE bus. This only has a 33* phase shift per filter. This does not change when the latency comp engine is turned on or off. When the filter frequency is raised to 5kHz the phase shift at 50 Hz is 24*. I never knew the EQ's shifted the phase. My analog console has very little phase shift in the EQ's. Interesting the things you learn when you start testing.
So it seems my best practice would be to let the mastering guys deal with the full range LFE OR find a better LPF to put on the LFE bus OR use the MOTU bass management function with a trim on the LFE bus inverting the signal back in phase.
I much prefer to leave the L C R speakers full range and only add the LFE when needed.

Sorry I'm rambling, it's been a long day...........

Don T

Don T wrote:Hello,
I have another question:
Is there a way to have the sends panning mirror or follow the main panning?

Don

Not that I know of.

What did MOTU have to say about the phase issue?

Don T wrote:Hello Again,
... I never knew the EQ's shifted the phase. My analog console has very little phase shift in the EQ's. Interesting the things you learn when you start testing.
...........

Don T

Analog eq is basically an AC circuit of capacitors and inductors that works by feeding the signal back on itself (with phase shift, which is caused by the components). This results in the audibly altered frequency response. The phase shift itself is not audible, being too small a unit of time. Digital filters mimic this behaviour.
Crossovers also introduce phase shift. Arguably the most ideal crossover ever manufactured is the Lake Contour Linear Phase system which virtually eliminates phase distortion - designed in Sydney and now owned and used in Lab Gruppen amplifiers (which, in turn, is owned by Music Group/Behringer).

Analog eq is phase shift by nature. The bbc used to call eq's phase distortion units way way back.

Hello Folks,
Well, I've gotten no reply on my 15 day old tech link about this. It's sitting there unread. Are they busy with something over there? I just updated to 9.0.1 but it did not solve the issues.

Don T

I've found that it can be a bit hit-n-miss with the timeliness of responses to Techlinks. If you have been waiting ~2 weeks, I would suggest going in and adding a note to your issue, with a link here.

If that doesn't work, I have used the MOTU contact page to get their attention. Squeaky wheels and all that.

Hello folks,
I have not gotten a reply to my Motu tech link. They are usually pretty good at communication but I must be in the gnore pile.

Just checked and it is STILL unread as of today 9/28/15, original TechLink started 8/5/15

Too late to call today..........