Film-Tech Forum ARCHIVE: How does one inject pink noise?

This is topic How does one inject pink noise? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=010713

Posted by David E. Nedrow (Member # 4981) on 11-22-2010, 03:51 PM:

There are test points on various bits of the USL JS 105/195 sound processor, through which one is able to inject pink noise.

My question is, how does one actually do that? On visual observation, the test points look like they're single pole. If I have a pink noise generator that puts out a 0 dB signal at line level, how would I input that into, for example, the JEQ-10 house equalizer module? If the test input IS single pole, what is used for the second pole? Chassis?

Posted by Gordon McLeod (Member # 33) on 11-22-2010, 04:27 PM:

the other pole is a e terminal to one on the optical preamp is easiset to reach

Posted by David E. Nedrow (Member # 4981) on 11-22-2010, 05:25 PM:

Thanks, Gordon.

Posted by Tony Bandiera Jr (Member # 2365) on 11-22-2010, 09:00 PM:

David, when injecting pink noise through those points be VERY careful as some of them are "post-fader" which means they will feed signal directly to the amps with no level control between! Very easy to blow out speakers if you aren't careful.

USL still has their plug-in pink noise card, get it if you can, it's not expensive and provides the proper levels to set room SPL correctly.

Posted by Louis Bornwasser (Member # 3063) on 11-23-2010, 03:11 PM:

You know, it might be possible to assemble an adapter card to allow this pink noise gen to work in a Dolby. Voltages and levels are probably similar. Louis

Posted by David E. Nedrow (Member # 4981) on 11-23-2010, 04:24 PM:

quote: Tony
USL still has their plug-in pink noise card, get it if you can, it's not expensive and provides the proper levels to set room SPL correctly.

I've been considering that, but I'm -- hopefully -- getting a new JSD-80 to replace this poor, abused JS 105/195 that I inherited.

I think there may be someone locally who has the USL pink noise card. I'm going to ask our service person if he can get in touch to see if we can borrow it for a day or two. I hate to spend $250 for something I'll probably have no need for in the near future. Though, if I somehow come up with space for a "screening" room, I could use this JS and amplifiers (being replaced as well) for that, meaning I would need the pink noise card.

I hate decisions like these. [Wink]

And I'll check the block diagrams for the test points to see where they fall in the chain. Thanks for the warning, as it wasn't something I thought of.

Posted by Manny Knowles (Member # 1171) on 11-23-2010, 06:25 PM:

quote: David E. Nedrow
puts out a 0 dB signal

0dBFS?

Posted by Steve Guttag (Member # 268) on 11-23-2010, 10:51 PM:

Nope...0dBv. The JS series had a buss level of .775V

-Steve

Posted by Manny Knowles (Member # 1171) on 11-24-2010, 03:38 PM:

I was gonna say... [Eek!]

(my point being...you can't just say "dB" by itself...it's not enough.)

Posted by Steve Guttag (Member # 268) on 11-24-2010, 05:09 PM:

It was, more or less, implied. I could understand the confusion between dBv, dBV (.775V vs 1.0V) but in no way should someone think that was dBFS

Posted by Manny Knowles (Member # 1171) on 11-24-2010, 05:53 PM:

I guess I'm just picky about insisting on a reference.