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 Post subject: Low end frequency response of an electrically recorded 78?
PostPosted: Feb Mon 25, 2019 2:20 am 

Joined: Apr Tue 17, 2012 7:58 pm
Posts: 121
Location: Metamora MI, 48455
To make a long story short, I'm trying to work out where the shelving frequency should be for a "typical" electrically recorded 78. Let's say circa 1938 or so when recording was fairly mature in nature, to the end of the 78 era.

In order to define a transform function for an equalization curve, you can't have a result which gives infinite gain at zero hertz, which is exactly what happens when you treat a 78 equalization curve as having no shelving.

Anyway, the solution is to simply treat the early 78s as having an equalization curve of three inflection points, two explicitly defined, and one defined by the lowest frequency the cutting head was capable of recording, which forms a sort of shelving function. This eliminates the "infinite gain at DC" problem. This un-intentional shelving will vary from cutting head to cutting head and also with the other equipment in the recording chain, and thus won't be the same from disc to disc.

Now the issue is, where do I place the shelving frequency for a "typical" electrically recorded 78 from 1938 to the end of the 78 era? Is there meaningful information at 20 Hz? 30 Hz? 40 Hz? Or does the meaningful information cut off even earlier at say 60 or 70 Hz? There must be some reasonable value to compromise on.

 Post subject: Re: Low end frequency response of an electrically recorded 7
PostPosted: Mar Fri 01, 2019 3:57 pm 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 11314
Location: Ohio 45177
I would go with what they use for LPs, a rumble filter that maybe cuts off below 20 hz. Then again it depends on what you are playing them on. On an old rim drive record player, there may be noise regardless of the filter and if you are using a modern player with a proper 78 type pickup, I would think the standard type of rumble filter would suffice. As you could go higher but then you are not talking a brick wall filter, it will have some effect above the corner frequency if you go with say, 30 or 50. Is hum an issue? I doubt the microphones or amplifier systems at the time could go much below 50 but why not go with the least effect into the audible band?

Reddy Kilowatt says; You smell smoke? Sorry about that!

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