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  #76  
Old 05-06-2014, 08:50 AM
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rick-slo rick-slo is offline
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Originally Posted by Ty Ford View Post
Sorry Rick, I don't think one can selectively apply the laws of physics as they choose.

Although the effects of comb filtering can be more obvious when both mics are in the same sound field, comb filtering, per se, does not demand that mics are close together. Maybe I'm missing something.

http://en.wikipedia.org/wiki/Comb_filter

I'm curious as to how the double EQ approach sounds when the resulting stereo mix is folded down to mono.

Regards,

Ty Ford
The first sentence from your link above is exactly my point-

"In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced spikes, giving the appearance of a comb."

-and of course that is (adding comb filtering by using a delay) exactly one thing that people do who record mono post recording to try to make it sound fuller and more spacious (more like stereo). If comb filtering is bad and you are trying to avoid it, that is the worst case scenario.

Getting back to stereo recording the only equivalently high degree of comb filtering to the mono case above (adding a delayed version of a signal to itself), would be recording a point sound source that radiates the exact same sound in different directions and miking it at different distances in an anechoic space , and volume matching the mikes. Of course if you miked at the same distance you would just have the exact same sound in both mikes - might as well have recorded with one mike.

A guitar is not a point source, does not radiate the same sound in different directions, and is usually not recorded in a completely dry room. All of that reduces the severity of comb filtering (it's depth and regularity) resulting from mike to source timing differences. An ambient distance mike even more reduced as the sound is different and the volume from it is mixed in at a lower level.

Again, the highest severity of comb filtering is going to be in one mike mono recordings where there is an attempt post recording to add a stereo field illusion with software.

All that said, timing differences (arrival of a sound to the right versus left ear) is the real world and part of how we process direction and distance. So it is not just a bad thing, but necessary for a more natural sound. Regarding timing delays in a recording, or post recording tweaking, control of which frequencies get boosted by it, which get reduced, and for how long, and in how regular a pattern are concerns for a better sound.
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  #77  
Old 05-07-2014, 07:15 AM
Ty Ford Ty Ford is offline
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actually, I think "In signal processing" is the key there as well. That implies the electronic phenomenon rather than the acoustic phenomenon.

If sounds are observed as wave fronts it's easier to wrap your head around their interaction in an acoustic space. I think people would be amazed if they were able to see how sounds really behave (or misbehave).

What about the phase cancellation due simply to the byproducts of EQ?

Then there's what happens if (when) the two tracks are folded back into mono as they will be when heard through a FM radio receiving a signal from too distant a transmitter with the "blend" circuit in, in an elevator, from a clock radio or from a variety of overhead sound repro systems.

I'm remembering the Yamaha DX7 keyboard that had these great spacious stereo sounds. When folded to mono, the sounds collapsed and all but disappeared because they were created by polarity flipping one channel and messing with it a little.

Nice conversation.

Regards,

Ty Ford
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  #78  
Old 05-10-2014, 09:35 AM
Anderton Anderton is offline
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Originally Posted by Ty Ford View Post

I'm curious as to how the double EQ approach sounds when the resulting stereo mix is folded down to mono.

Regards,

Ty Ford
If you get the "combination lock" for the filters right as alluded to above, the collapse to mono simply sounds like a mono version of the stereo. However, I've done this only with digital EQ, which I presume helps with the predictability.

As to comb filtering, whenever we hear anything in a room there's comb filtering - it's unavoidable. It would be interesting to find out if a little comb filtering could actually be an aural cue for "realness" if the second audio signal is lower in volume and delayed somewhat, as opposed to two mics close together where you can actually hear some notes get weaker.

I'm still waiting for a way to make a recording sound like someone is playing in a room with you. I suspect I'll have a long wait
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  #79  
Old 05-10-2014, 12:35 PM
Fran Guidry Fran Guidry is offline
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...

I'm still waiting for a way to make a recording sound like someone is playing in a room with you. I suspect I'll have a long wait
You might consider the possibility that you already have such recordings - but lack playback equipment capable of delivering the result successfully.

Fran
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Old 05-10-2014, 02:46 PM
Ty Ford Ty Ford is offline
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I'm still waiting for a way to make a recording sound like someone is playing in a room with you. I suspect I'll have a long wait
Some time ago, I was demoing a Gefell M296 nickel membrane omni mic. I had heard that nickel membranes were significantly better than gold.

It was surprisingly "real." I had a friend come over to record some of his acoustic guitar stuff. I burned it to CD. The next day he told me his wife came down stairs to the music room and was surprised the see he wasn't playing. From up stairs, she thought he was playing live.

Ah, still have something I recorded with it.

https://www.dropbox.com/sh/na22y11ba...92noCqV2epkUda

Regards,

Ty Ford
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  #81  
Old 05-10-2014, 08:00 PM
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rick-slo rick-slo is offline
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There are phase non-alignments (comb filtering being a subset of that) in every room. With a guitar there are even phase non-alignments coming right off the instrument itself.
So any mike will be presented with phase non-alignments right at it's diaphragm. With the same set of non-alignments presented to each ear it's just a change in tone (usually
thinned out). With a different set of non-alignments presented to each ear some of that is resolved into ambience rather than primarily a tonal chance (since this is how we hear
things in the real world).


Regarding a recording that sounds like the real thing, it is mainly an issue of realism in ambience recreation rather than of tonal recreation. More than once I have hear what
I thought was a guitar being played live when I was hearing speakers playing while I was some distance away, usually in another room. The real world combination of reflections
off the floors and walls, and around a corner or two gave an ambience which seemed realistic.
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