Um400 - SRa combo - anyone hear digital compression in high noise environments ever?

[rianengelen]

Hope to hear some thoughts on this, whether it is actually something I'm hearing is hard to tell, or whether I'm just being pedantic and need to accept the fact that I'm working with a boom on the beach right by extremely noisy ocean surf.

 

Here goes:

 

Running a boom track via a lectro hop to camera on the beach with a lot of ocean surf noise in the background, this surf noise is pretty constant, and would sound very similar to the white noise generated in a building except and obviously a lot louder. In this particular situation it is impossible to use lavaliere mics, which would obviously have worked best.

 

This is the kind of situation where we have to shoot right by the ocean on a noisy, heavy-surf beach, only able to break away for controlled scenes away from this noise when the time allows.

 

Super cardiod mic I'm using: Sennheiser MKH70 - which provides great off-axis rejection of any environmental noise.

 

Im running this in to a Sound Devices 302, 3 channel mixer. The limiter of the 302 is set above my peak, to ensure for the sake of this test it is nothing to do with the 302 limiter.

 

I'm running mic level into a UM400a and transmitting my boom this way to a Sony f800 camera with a Lectro SRa receiver in the WRR slot. 

 

Gain structures all set correctly on the tx and camera. Limiter on camera is on, but only set to start working at a threshold above my peak recording level on camera for this test. Peaking at -12dB on camera with a constant voice.

 

When I listen back to tape after a day of recording, sound is good - especially and obviously all segments shot away from the surf), but in listening back to the recordings done in the noisy surf I wonder if I hear some sort of slight digital compression in the lectro link, almost as if it were a compandor squashing the background noise. This is impossible as there is no companding happening on the Digital Hybrid audio signal to begin with, right? Companding only happens on the rf carrier signal as I understand it... after all analog signal has been converted to digital.

 

Again this is so slight, it is not attributable to any equipment fault, and most likely is me over-analysing. I was wondering if anyone has ever operated this combo in this situation and experienced anything remotely similar? Or am i an idiot and simply hearing the ocean noise grow and dissipate over a constant voice recording, as sets come in?

 

 

[fieldmixer]

post a sample

[JDirckze]

So are you listening back off tape from the camera?

Are you rolling your own recorder at the same time?

I run a nearly Identical setup on the show I'm on at the moment, but haven't done any critical listening back off tape as the headphone output isn't of high enough quality, and I don't have access to an XDCam deck.

Does the same noise happen when running at Line level into your UM400's and SRa?

Edited July 27, 2014 by JDirckze

[LarryF]

Possibly the noise reduction function in the transmitter? That manifests itself as a variable high pass filter on low level noise so if it were happening it would show up as a reduction of the high end on random noise, i.e., the surf. If the noise is moderately loud or greater, the filter moves out of the way. In use, if you think it is removing desired noise, it can be switched off in the menu on the transmitter.

Typically the filter will remove lavaliere hiss and some low level room noise (air handlers, etc.). This strictly a guess as we don't have much surf background in New Mexico to use as a test.

Best Regards,

Larry Fisher

Lectrosonics

[soundtrane]

<This strictly a guess as we don't have much surf background in New Mexico to use as a test.>

 

lol!!

[soundtrane]

<In use, if you think it is removing desired noise, it can be switched off in the menu on the transmitter.>

 

Larry, where in the UM400a is a menu? :~

[LarryF]

<In use, if you think it is removing desired noise, it can be switched off in the menu on the transmitter.>

 

Larry, where in the UM400a is a menu? :~

Boy, I didn't have enough coffee this morning. Back to the intravenous drip.

One, the UM400a doesn't have a menu.

Two, the noise reduction choice is in the receivers anyway.

 

I don't mind blowing it once but twice in the same post? Good grief.

Best Regards,

Larry F

[rianengelen]

JDirckse running mic level into 400a haven't run line. It's not so much noise produced (signal to noise is absolutely great) it may be the attempt to reduce it that I may be hearing. will be doing tests rolling my own recorder at the same time, thanks for the suggestion. that's probably the best way to determine if I am hearing what I think I may be hearing, again only in that worst case scenario where most people wouldn't be recording audio anyway.

[rianengelen]

LarryF thanks for the suggestion will see if switching the noise reduction "off" makes a difference in transparency. Again, it is incredibly slight if at all, and may just be the ocean itself in some of the worst conditions imaginable to record audio.

[soundtrane]

Dear Larry - may you never need an intravenous drip! 

 

Love you man!  

[rianengelen]

Hey All

 

Completed tests... it is indeed the noise reduction on the SRb receiver. You hear it working in the surf conditions, and even with large gusts of wind. Switching noise reduction off increased transparency adequately.

[LarryF]

Hey All

 

Completed tests... it is indeed the noise reduction on the SRb receiver. You hear it working in the surf conditions, and even with large gusts of wind. Switching noise reduction off increased transparency adequately.

Thanks for the update. In those conditions, the noise reduction is not going to do any good on lavaliere hiss or "room noise" since any low level hiss is more than covered up by the surf anyway. Note, we did make it selectable for a reason.

 

There is a psycho-acoustic phenomenon in which low level hiss pre-sensitizes the ear to detect more high frequencies. This plagued Ray Dolby for years as his various processes were accused of removing highs from tape recordings. He finally started demonstrating Dolbyized recordings with some hiss added back in to show they sounded like a straight recording without Dolby. This is not your situation but I just wanted to point out that low level hiss can alter the perception of even critical listeners. This might be part of the reason for "vinyl aficionados".  But that is  a whole 'nother discussion. The ear may be a wonderful instrument but it is not fool proof. All this to say, the receiver noise reduction generally does good things. 

Best Regards,

Larry F

Lectro