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Topic: What causes that hum?
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Andrew Woodcock
Film God
Posts: 7477
From: Manchester Uk
Registered: Aug 2012
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posted April 06, 2016 04:21 PM
Some machines certainly score worse than others regarding ground hum from the Super 8mm range.
Findings from the recent ones I've used or witnessed are;
1/ Eumig S938 - hardly any
2/ ST 1200 is not bad at all on this front, especially the HD.
3/ Beaulieu Stereo - hardly any at all until very high volume level is reached.
4/ Bauer models - awful for ground hum until the heads load. Then they are fine (ish), especially the later 525 / 610.
5/ Agfa Sonnector, not great either for ground hum
6/ Elmo GS 1200- some but not overwhelming by any means.
To me its more of an offense, the circuit's that don't ground the loop hum from head and transformer when they are idle like the Bauer Studio range. It's very annoying having to quickly lower the volume slider as a film reaches its end. A bad design here in that one respect.
As Steve says, ways to solve include extra grounding wherever possible especially on input / output connections to separate equalizers and amplifiers and the inclusion of devices like ground loop isolators for placing in circuit,in between such devices.
Also much of this issue here can be purely down to some of the ridiculously low recording levels that come with our films originally. If you are having to really crank that volume pot to gain anything like reasonable listening levels of audio, then it's only to be expected, that of course some hum and hiss will follow from a magnetic track of any kind.
If levels are high, touching 0db for peaks or thereabouts, then even the worse offenders here sound very very good comparatively.
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"C'mon Baggy..Get with the beat"
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Gary Crawford
Jedi Master Film Handler
Posts: 979
From: Manassas, VA. USA
Registered: Jun 2003
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posted April 07, 2016 09:15 AM
Having been in the audio world for my job for almost 50 years, I'd say hiss is the hardest darn thing to handle. You want ALL the high crispness of the soundtrack. You don't want the hiss. Most times the two are unfortunately co-mingled. Some of that hiss is right in the middle of the frequencies you want to hear in the track. Eq or filter too much and you almost always take out some of that good frequency range in the original sound. It's almost always, especially with consumer equipment, a compromise between the sound you WANT to hear and the his you DON'T want to hear.
Generally in well recorded soundtracks the rolling off of highs is not needed. The sound obliterates it. That's why I don't recommend trying to eq the hiss or hum from a source like a projector with no film running. Sure, you can filter the heck out of the amp noise, but when you go to run a film, you end up with half the highs on the track gone and some of the lower frequencies gone, too.
it's a tough job.
The older Eumig's pre HQS 800 models had so much hum, it was distracting, even when a film was playing. Since then the 824's made a big improvement. The Elmo st1200HD series have some amp noise that seems to dissolve once you have film running to cover it up. The GS is better. Both have more noise coming out of the power amp, the one that feeds the speakers, than coming from the aux out or monitor lineout outputs.
Great, careful recordings using machines with good sound heads, properly aligned and clean, recorded at good levels, properly biased for the type of sound stripe....all these things really can make a world of difference in how Super 8 soundtracks can sound.
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Steve Klare
Film Guy
Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003
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posted April 07, 2016 09:30 AM
'Morning Gary!,
Hiss is definitely a situational thing. That's why I keep a flashlight back by my machines. Unfortunately the folks that built my mixer panel never expected it to be used in the dark!
I always run with the 60Hz notch, though. It doesn't kill the projector hum entirely, but it so thoroughly injures it that any normal soundtrack overwhelms it. (-even just the other ambient sounds in the room...)
There is still plenty of bass left.
The day somebody in a musical hits the second "B" up from the bottom of the keyboard, that note will get hurt, but so far I've gotten away with it!
I think there is a fair amount of psychology going on with this stuff too. If you turn on modern consumer electronics, you have to crank the volume up to disastrous levels to hear any kind of hum at all.
-then we use a 40 year old movie projector and listen to it with that same set of ears.
I bet a 40 year old TV or stereo would seem hummy to us too!
I didn't think my Elmo STs were hummy when I was operating on the internal speaker, but these days every time I operate unplugged from the external setup they sound absolutely awful! (especially at first...)
-just expectations!
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All I ask is a wide screen and a projector to light her by...
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