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Author Topic: Combining 2 mic inputs to one recorder  (Read 487 times)

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Offline Massive Dynamic

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Combining 2 mic inputs to one recorder
« on: February 19, 2020, 09:33:17 PM »
Did a search, no luck, so I'm hoping someone can provide some expertise.

I have two microphone rigs, but only one recorder. Both rigs terminate in stereo 1/8" plug, and I wondered if a y-cable could allow signals from both rigs to be synched and recorded at once. The cardioid rig only has frequency response down to about 50Hz, so I'd like to augment that with the low end response of the omni rig.

Thinking of using a Hosa YMM-232 to accept dual stereo 1/8" plugs and combine them to a single stereo 1/8" plug to go to the M10. I know there might be signal level issues (still need to do some living room stereo testing) between the two sources, but I'm curious if the y-cable will do what I think it will.

The card rig rig doesn't have any volume adjustability, but I have a SP battery box with level attenuation for the omni rig that might get the signals close. Is this a fool's errand?
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Offline beatkilla

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Re: Combining 2 mic inputs to one recorder
« Reply #1 on: February 19, 2020, 10:07:22 PM »
The Tascam DR-2d recorder can record Mic Input AND Line input at the same time seperatly.You can make 2  stereo recordings.This is way better as you can mix later in post.Just my opinion of course.

Offline DSatz

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Re: Combining 2 mic inputs to one recorder
« Reply #2 on: February 20, 2020, 06:24:47 AM »
If you simply combine (via a Y-adapter) the signals from two microphones into one channel, the results may vary, but you are quite likely to compromise the sound quality severely.

In most specification sheets for microphones, there's a figure called "recommended load impedance" which is generally 1000 Ohms or higher. This represents the minimum value for that type of microphone; with lower load impedances some proportion of the signal will be lost, distortion will increase (especially at high sound pressure levels), and in extreme cases the microphone may not function properly or at all. The thing is, if you use a Y-adapter to combine the signals from two microphones, you're placing their outputs in parallel--each microphone then "sees" the other one's output as part of the load that it has to drive. And the output is generally a much lower impedance (typically 1/10 the recommended load or less). So you probably won't get a very good sounding result this way--and you could, in an extreme case, damage one or both microphones. Powering the microphones also becomes an issue.

There are two ways to get around these problems: "microphone mixers" and "microphone combiners". Both types of equipment have multiple inputs and (in general) some smaller number of outputs. When you plug two or more microphones into either type of equipment, the outputs of the microphones aren't connected together directly; resistors, transformers, and/or active circuitry are used so that each microphone "sees" the type of load it was designed to operate into. Mixers are more flexible because they let you set the amount of each microphone's signal that goes into the combined result--but most mixers contain active circuitry, and thus require their own power source (which may be a battery). There are, however, some purely passive mixers. A "combiner" usually uses a transformer with separate primary windings for its two microphone inputs, and a single secondary winding that drives the output. That's a completely passive arrangement, so no power supply is needed--but the only combiners that I know of are for microphones with professional-type XLR outputs, which isn't the type that you have, so someone else would have to recommend one if that's the way you want to go.

Apart from all these electrical issues there's an even more basic problem. Simply combining the outputs of two microphones, which are relatively close to one another in the recording venue, is a mixed blessing. Because different sound frequencies have different wavelengths, and both microphones are receiving the same sounds but at slightly differing times (because of their different distances from the sources), when their signals are combined, some frequencies will be reinforced while others will be diminished (partially canceled). The result can sound rather strange and artificial, and not what you want or expect; it's a game of chance. Most professionals avoid this type of situation as much as possible (see "3-to-1 rule" on the various Internets).

What a lot of people here seem to do is mix the output from the venue's sound board (if they can get at it) with their own recording. That's different because the balance and timing of the signals from various sources will be different from one another; each means of pickup could fill in something that was missing or unclear in the other.

There's also an effect that occurs when you have a s**t-ton of microphones in different places, all competing with one another to render the same sound sources: the mixture is so chaotic that no one conflict predominates in the resulting mix, since basically everything is in conflict with everything else. I don't generally like that kind of recording--but it can work in its own way, as long as there are enough separately-placed microphones to "swamp" the sound of the main stereo pair. At that point you can often remove the main pair from the mix entirely, and not notice much if any difference.

--best regards
« Last Edit: February 20, 2020, 02:07:08 PM by DSatz »
music > microphones > a recorder of some sort

Offline Massive Dynamic

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Re: Combining 2 mic inputs to one recorder
« Reply #3 on: February 20, 2020, 11:25:54 PM »
^ Thanks, an electronic issue due to a simple combination cable was what I expected. Even if it had been possible, the sonic effects probably would have exhibited the poor results you describe. I'll simply have to decide which mic pair is going to give me the sound I want in each situation.  :coolguy:
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Offline DATBRAD

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Re: Combining 2 mic inputs to one recorder
« Reply #4 on: February 21, 2020, 07:37:13 AM »
Run the cards and EQ in post slightly boosting the bass. The published specs for most mics show a frequency range based on a flat response within a couple decibels. The signal rolls off outside the upper and lower limit stated, it's not a hard cut off. That means you will have audible signal below 50hz, you just have to increase it's level in post. Good luck!
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Offline Massive Dynamic

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Re: Combining 2 mic inputs to one recorder
« Reply #5 on: February 21, 2020, 10:07:06 PM »
Run the cards and EQ in post slightly boosting the bass. The published specs for most mics show a frequency range based on a flat response within a couple decibels. The signal rolls off outside the upper and lower limit stated, it's not a hard cut off. That means you will have audible signal below 50hz, you just have to increase it's level in post. Good luck!

I've done what you suggested. The mic is actually rated down to 40Hz. Doing a quick eq, adding several dbs to the 40 Hz range made no significant difference. Adding to the 50 Hz range was audible, and +3db was about right (+6db was too much for an extended listen).
Naiant X-X > SP-SPSB-1 > M10
Superlux S502 > Denecke PS-2 > Hosa MIT-435 > M10

 

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