Film-Tech Forum ARCHIVE: Light 'buzzing' while showing live satellite broadcasts

This is topic Light 'buzzing' while showing live satellite broadcasts in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Steve R Pike (Member # 6238) on 05-14-2014, 01:33 PM:

Hello, firstly let me give you a list of the tech gear we are using:

Icecrypt S4000HDPVR (Satellite Box)
Denon AVR 1908 (Receiver)
Christie CP-2000-S with CineIPM 2K(Projector)
Dolby CP650 (Sound Processor)

For some of our live transmissions, there appears to be a faint 'buzz' in the background. It may be down to the live broadcast picking up sounds like air con or other sounds from the performance venue, however it appears to happen on two separate broadcasts (National Theatre Live and RSC Live). MET Opera doesn't seem to have this issue.

A HDMI is plugged into the Denon receiver from the Icecrypt box. Then a HDMI comes out of the Denon and into the CineIPM on the Christie projector.

Cables then go out of the Denon and into a patching bay called a 'DAP-1' (with Project Research Ltd on the front)

That's the setup. We have no issues with picture, but only with sound with the slight buzz in the background.

Does anyone have the same setup and/or know how to stop this buzzing? The Denon also always displays 'NEO: 6C' - in the past it has displayed Dolby Pro Logic. But the manual doesn't give me much guidence on how to set it to Dolby Pro Logic (if that would make the issue better at all?)

Thanks

Posted by Paul Willmott (Member # 3904) on 05-14-2014, 02:05 PM:

I assume you are using the Denon to get analogue audio. It should be set for Dolby Digital (not prologic) and the Icecrypt should also be set for Dolby Digital output. I'm not sure if this is the problem, but you do need these settings to get the correct 5.1 sound.

Posted by Geoff Newitt (Member # 6663) on 05-14-2014, 03:09 PM:

Hi Paul

Are you one of our customers? That is - do you get tuning guides and 'support' from Charlotte Hines and David Newlan at Picturehouse?

If so, ask them to put you in touch with me direct - I'm Picturehouse's Head of Tech, don't mind lending a hand if you're stuck.

Posted by Paul Willmott (Member # 3904) on 05-14-2014, 03:18 PM:

Hi Geoff

It's not me that's stuck but Steve - all ok here at Saffron Screen!

Paul

Posted by Carsten Kurz (Member # 5396) on 05-14-2014, 05:00 PM:

Wondering why the audio is not fed directly through S/P-DIF from the SAT-Box to the CP650? The receiver inbetween will probably have an analog connection to the CP650, and besides that, it adds unnecessary complexity.

- Carsten

Posted by Geoff Newitt (Member # 6663) on 05-15-2014, 09:24 AM:

Ah, yes... Sorry Paul, I'm easily confused!

Steve - obviously that was aimed at you!

Posted by Mike Olpin (Member # 1115) on 05-17-2014, 01:49 PM:

Carsten is correct. You should go directly from the satellite receiver to the sound processor. You are probably picking up a ground loop hum in the A/D conversion. I suspect the analog output from the Dennon is not balanced. If you use consumer grade equipment, you will get consumer grade results. A Dolby DMA 8+ is a professional grade device that will do A/D and provide a balanced analog output.

Posted by Pete Naples (Member # 761) on 05-17-2014, 03:55 PM:

You assume the 'CP650' is actually that, I find most people call them all CP650s, when they are CP650D, CP650SR etc.

Could well be there's no spdif input on it.

Posted by Geoff Newitt (Member # 6663) on 05-26-2014, 01:34 PM:

Plus the Topfield has only an optical spdif, whereas the one on a CP650 is copper. The converter might only be £15, but if you don't have it to hand...

Denon AV receivers have been extensively used in the UK with great success; usefully, they made a couple of models with line level pre-amp outputs. Unbalanced for sure, but very often these were fed via a (sub pass modified) DA20 into CP55 or CP65, so the complete path was unbalanced. I've not really encountered hum or buzz before - convincing people never to turn the 'volume' up beyond 0dB is the usual problem. (To digress, one cinema which kept complaining of distorted sound on satellite shows had the Denon set to +13dB!)

A lot of early UK d-cinemas only had pretty basic DACs, and not all have upgraded despite the falling price of DMA8+/CP750.