Recording sound from a projector

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Recording sound from a projector

Post by Andreas Wideroe » Sat Feb 25, 2006 3:20 pm

I'm trying to record OK sound from a Bauer T280 multiformat onto my PC using a DIN to minijack cable plugged from the projector, through my Yamaha MG16/6FX mixing table and into the line in of my PC. I'm using Nero Wave Editor to capture the sound.

However I'm having big problems with noise from the projector. Sounds like electric background noise or some bad shielding or something. I guess the projector wasn't built for HiFi, but I've tried two cables and this was custom made by Wittner and should work.

What I'm asking is are there any things I could do with the projector to limit this background electric noise?

Here's a sample mp3 file (about 500kb). Not quite sure if you will hear the noise in this file since my laptop speakers are so bad, but I think it will give you an idea.

Another question is are there any simple "boxes" I could put between the mixer and the PC to remove this type of noise?

Cheers,
Andreas
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Post by aj » Sat Feb 25, 2006 3:39 pm

Sounds like a earthing problem. Connect all gear to the same mains-earth.
Kind regards,

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Post by MovieStuff » Sat Feb 25, 2006 3:40 pm

Sounds like basic 50/60 cycle hum to me. Just run it through an equalizer and drop the lower end where the hum exists and the rest of the audio should be pretty much unaffected. A notch filter would be ideal, if you can isolate the cycle rate on the hum exactly.

EDIT: AJ was posting at the same time. Yes, it could be a grounding problem. That would produce similar hum.

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Post by BolexPlusX » Sat Feb 25, 2006 3:48 pm

What I hear is powerline hum, and what it is is because within the confines of the projector you have a large transformer putting out a magnetic field and also a very sensitive soundhead which unfortunately picks it upand mixes it with the signal on the stripe.

It is line frequency and the next couple of harmonics above it (for you: 50,100,150,200 Hz.), (for me 60,120....). I've tried filtering it out, but unfortunately this interferes with the bass and makes the sound a little tinny.

Many projectors have inductors mounted by the soundhead which are intended to pick up a sample of the hum and subtract it out of the signal. Some people have had luck adjusting the orientation of these coils to better cancel out the hum.

I found a circuit which develops a signal equal and opposite the hum and uses it to cancel it out without killing the bass. This is how I plan to deal with it.

http://www.ethanwiner.com/filters.html

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Post by Andreas Wideroe » Sat Feb 25, 2006 4:09 pm

Thanks!

I'm pretty sure it's 50hz hum. Sounds similare to some other "old" equipment I have when hooked up to a stereo.

There seems to be VST plugins for hum removal which I'll try and find for testing.

I wonder if taking out the power supply and placing it next door will help? :wink: Will probably be a hazzle though...

Sometimes I wish I was an electronician! :roll:
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Post by audadvnc » Sat Feb 25, 2006 8:34 pm

The audio amplifier's power supply capacitors have dried up. If you intend to use that feature, take the projector to an electronics repair shop and have them replace the power supply caps. This is a standard repair procedure for all old audio gear.
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Post by BolexPlusX » Sun Feb 26, 2006 5:20 am

The theory that the electrolytics in the power supply were old is a good one, but unfortunately this hasn't helped in the cases I've tried. Because modern capacitors are actually much higher values in the same package, I was able to go to higher values than original, and still I have hum at an intrusive level.

(This is still worth trying, by the way. You can do it yourself if you can find the part and you're good with a soldering iron.)

If they were to build a projector these days, they'd have it powered by a switching power supply operating at 100 kHz or higher so there wouldn't be all these audio frequency magnetic fields in the same case with the sound head, but that's not what we have to play with.

(Andreas' idea of taking the transformer and mounting it remotely probably has some merit, even though it's a bear for portability!)

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Post by David M. Leugers » Sun Feb 26, 2006 7:01 pm

Thinking outside the box, so to speak, if you are using the projector for only transferring of film and don't worry about resale value, why not try removing the power supply completely out of the projector case and running wires into the projector from the external power supply? If far enough away, how can the power supply affect the sound head? Just a thought.


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Post by BolexPlusX » Sun Feb 26, 2006 10:16 pm

This should help, the only remaining problem would be the field generated by the windings on the motor. However, the fewer the sources, the easier to shield against them.

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Post by mattias » Sun Feb 26, 2006 10:42 pm

won't the power supply transmit any hum through the cable anyway? are we sure it's radio interference picked up by the sound head?

/matt

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Post by BolexPlusX » Sun Feb 26, 2006 11:05 pm

I'm pretty sure that the major problem is pickup, because the capacitor change I mentioned above (the first thing I tried), should have cut the power supply ripple way back, yet the change in hum wasn't noticeable.

Once again, the capacitor change is easy, and a good first thing to try fixing. If it works, so much the better.

I think part of the problem we're up against is that the original designers were thinking in terms of playing through the internal speaker on the projector, which is pretty poor bass-wise, but then we go putting better transducers and circuits on the output, which really brings up the hum.

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Post by MovieStuff » Mon Feb 27, 2006 12:06 am

In all my years farting around with super 8, I never had a sound projector that did not have some minimum level of hum present. I wasn't really surprised when I heard it on Andreas' sample. Very nostalgic, really.

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Post by Ericus » Mon Feb 27, 2006 12:23 pm

I had a similar problem, which I solved buying Creative´s external Sound Blaster NX2 sound system, and no hums at all!

I use Pedro´s P1008GS-U sync control with my Elmo GS 1200 and my WorkPrinter to transfer my sound films.
For me NX2 worked fine, and it didn´t cost much.

http://www.soundblaster.com/products/pr ... oduct=9103

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Bauer noises at sound transfer: two reliefs

Post by Bart Sanders » Mon Feb 27, 2006 12:38 pm

Hello,

Sounds like a 50 Hz hum problem. Two reasons why it's there: internal circuitry of the Bauer not OK or never has been OK, or, you have a so called ground loop. Try removing one ground point, bes option is to do that at the DIN plug, ONLY use the signal wire(s).

Second relief, if the above is not solving it: use Adobe Audition and filter out the 50 Hz hum. This program is very good in doing that. There are predefined filters, or you can "teach" it to listen to your particular noise and then remove it.

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Post by S8 Booster » Mon Feb 27, 2006 12:58 pm

its just typical for all sorts of projectors some worse some better for all reasons mention above. some has real design flaws.

Pedro posted an advice for the bauer t610 series which has a design error as well. really humming that one.

you may disconnect the wires to the sound heads and connect them directly with some hq mike input on a recording device. hum gone unless you place the wires over the main transformer.

my gs1200 is pretty noise free though. can do the job with it if you like.

the other option is to add software audio filter as mentioned above. try to kill anything below 150-200hz for a start. i have a demoware sound studio with a 30 band equalizer and multiple variable hi and low pass filters. will do.

some softwares can even be taught which noises to reject as well if you can identify its waveform.

my best recommendation is sw if you do not require the absolutely highest level of audio quality.

s8hôôt
..tnx for reminding me Michael Lehnert.... or Santo or.... cinematography.com super8 - the forum of Rednex, Wannabees and Pretenders...

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