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Author Topic: Best Mic for Lectures?  (Read 1225 times)

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Offline retailgeek

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Best Mic for Lectures?
« on: March 24, 2018, 02:21:18 PM »
I realize this isn't the primary use-case for this forum, but I'm a podcaster that records his show on a Mix-Pre6, and get lots of good info from this forum.  And now I have a new application.  For some podcast, we're commented on a lecture/presentation given on stage, so we want to capture some of the audio of the presentation.

For podcasting, we usually use dynamic mics (we're not recording in ideal rooms, so trying to minimize background noise), like RE-20s, or SM58s (on the road).  Any suggestions on the best type of Mic (or specific MIC suggestions) to record a speakers voice coming through a PA system in a large room.  It doesn't have to be stealth but smaller size makes it easier to transport.

I'm guessing a condenser with a directional pattern, and point it at a speaker? 

Offline kuba e

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Re: Best Mic for Lectures?
« Reply #1 on: March 24, 2018, 04:18:46 PM »
For podcasting, we usually use dynamic mics (we're not recording in ideal rooms, so trying to minimize background noise), like RE-20s, or SM58s (on the road).

Dynamic mics don't reduce background noise. They capture sounds equal as capacitor mics. You may have mistaken because the dynamic mics has lower output signal (you need more preamp gain). But this does not mean that it records distant sounds differently. It records them exactly same as capacitor mics with same polar pattern. You can lower background noise only by to be closer to sound source or by mic directional pattern.

You can try to place a pair of condenser mics in the room and record speaker's mic too. Then you can find the ideal ratio by mixing the dry direct sound (SM58) and ambience sound (room mics). When placing room mics you should take in account whether you want to record audience reaction too. Use some sensitive condenser or electret mics for micing room, dynamic mics have very low output for this sound level.
« Last Edit: March 24, 2018, 04:36:15 PM by kuba e »

Offline retailgeek

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Re: Best Mic for Lectures?
« Reply #2 on: March 25, 2018, 01:52:20 PM »
Dynamic mics don't reduce background noise. They capture sounds equal as capacitor mics.

OK, but because dynamic mics are less sensitive, doesn't that allow for a shorter working distance, which has the effect of making the hosts volume louder relative to the room noise?  I'm an audio newby, so I'm not arguing, I'm honestly asking to try and learn.  It seems like I've read that most pro VO people use large diaphragm condenser mics (Neumann U 87) that capture the richest audio but that they mostly work in carefully treated booths.  Whereas most radio shows in noisy studios use dynamic mics (RE-20, SM7B, etc...). 

Since I'm mostly recording in Hotel rooms and/or the spare bedroom at home I assumed I'm best off with dynamics.  So we use RE-20's at home, and SM58 on the road.  Full disclosure, I've actually switch to a Beta 87A on the road (with is a condenser) but supposedly one that has similar sensitivity/working distance to a dynamic.  Note that when we record on the road were also most likely to have live guests, so often it's 4 mics around a table.  So one consideration is something that works best with inexperienced talent.

I'm recording into Mix-Pre3 (at home), and Mix-Pre6 on the road so have decent pre-amps.  At home I also have a CL-1 cloudlifter on the RE-20.

I'm totally open to considering different mics.

Offline 2manyrocks

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Re: Best Mic for Lectures?
« Reply #3 on: March 25, 2018, 02:25:58 PM »
I am not clear on your situation.  if you are just recording off a pa speaker, you could put an sm58 in front of it.  if you cant get close enough to the pa, then maybe a hyper pattern mic would help cut down on room reflections.

if you could put lavalier mics on each person speaking and record them directly into a recorder, that would give you the cleanest audio signal.  if they are being micd into a soundboard, you might take a split off the board into your recorder.

again, i am not clear on what situation you have...

Offline kuba e

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Re: Best Mic for Lectures?
« Reply #4 on: March 25, 2018, 04:43:10 PM »
OK, but because dynamic mics are less sensitive, doesn't that allow for a shorter working distance, which has the effect of making the hosts volume louder relative to the room noise?  I'm an audio newby, so I'm not arguing, I'm honestly asking to try and learn.  It seems like I've read that most pro VO people use large diaphragm condenser mics (Neumann U 87) that capture the richest audio but that they mostly work in carefully treated booths.  Whereas most radio shows in noisy studios use dynamic mics (RE-20, SM7B, etc...). 

Me too, I am newby. I like the theory, but it is just hobby, everything may not be right. Dynamic mics are capable of handling high sound pressure level SPL (it is different property than sensitivity). It is the reason why you are able to put it close to the source.  But condenser microphones today can handle very high spl too. So this difference is erased. Advantages of dynamic mics are resistance against rough handling, moisture and are cheaper. Disadvantages are that they have less detailed sound - this may be sometimes advantage, and have lower sensitivity - are not good for recording from bigger distances.

I cannot help with practical advice, I have very little experience. I am recording lectures with cheap pair of lavalier primo EM172. I usually put it near the teacher, but not very close. And because they are omni, they also capture questions (and noise) from audience.

Edit:
An explanation of what the sensitivity and SPL are. The higher the sensitivity of the microphone, the higher the electric signal for the given sound level. When recording low level volume with low sensitivity microphone you get low electric signal.  And because all mics have some self noise, you have the ratio of noise/signal too high. It is why dynamic mics are not suitable for recording low volumes.
SPL - sound pressure limit is another property. It is saying how high volume is mic able to handle.
« Last Edit: March 26, 2018, 04:32:24 AM by kuba e »

Offline DSatz

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Re: Best Mic for Lectures?
« Reply #5 on: April 16, 2018, 08:38:29 AM »
My first question would be whether the podcast is delivered in stereo or in mono. If by chance it is delivered in stereo, then by all means, record the lectures in stereo and keep them that way when you mix! The recordings will be far more engaging, and the words will be far more intelligible to your listeners for any given microphone type or miking distance that you use.

Your facts about the higher output levels of condenser vs. dynamic mikes are basically correct, but the conclusions that you draw from them would be relevant only if for some reason, your recording device can't handle the signal levels that a [studio] condenser mike would put out in the type of recording that you're doing. It would be a concern if your mike was very sensitive and was placed inches from a guitar amp during a heavy metal show. But you're talking about voice pickup from a distance, where the signal levels are much, much lower. Any preamp / mixer / recorder whose inputs could be overloaded under those conditions would be pretty unusable for live recording in general.

The most important thing is not the choice of microphone but its placement. If you can get your mike onto the podium or tap into the P.A. system, fine. If you can't, (as a distinct second choice) aim the microphone at a P.A. system loudspeaker from close range--12" to 18" away, maybe. The reverberation of the hall is your dire enemy, and it starts MUCH closer to the source than you probably realize--the human brain is very good at filtering that stuff out, but it depends on having the input from two ears and (to some extent) your eyes as well. Most people are unaware of the extent of that until they start recording and listening to the results.

Once you have a clean, "dry" (= little or no room echo) recording, you can equalize to taste as you mix the recorded signals into your podcast--for speech recording, this usually means reducing the "boomy" low- and low-mid-frequency sound due to microphone proximity and/or the P.A. loudspeaker if you ended up miking one of those. As a side benefit, a low cut or rolloff will also reduce any handling noise and some environmental noises.

Finally, back to the choice of a microphone: As I said, stereo is greatly preferred; one-point stereo microphones are quite common, and nearly all will have the kind of curtailed low-frequency response and moderately boosted mid-high-frequency response that are your friend for voice recording. Most of these nowadays are "electret condensers" which is a nice compromise of economy and operating simplicity--many can be powered directly by your recorder, while others may require an internal battery, but the battery should last a good, long while--just be sure not to leave a battery in a microphone (or anything else) for months on end; when they eventually leak, the equipment can be ruined.

If you're recording in mono, then the "driness" of the recording (= miking close to the source, with a directional microphone that's accurately aimed) becomes urgent, because you've lost the ear/brain processing that makes such recordings easily intelligible. The thing is, directional microphones are also more subject to handling noise, solid-borne sound, breath noise, and "popping" on consonants (p, b, etc.) than typical omnidirectional microphones are, so those are issues to consider. One possible compromise that might be useful is boundary layer (or "pressure zone") microphones, which can create the effect of being somewhat closer than they really are; there are both mono and stereo versions of those, at all levels of quality and cost.

--Over the years I've done a fair amount of documentary sound recording with professional gear, and I have some pride at the quality of many of those recordings. But the most important thing is to get there and get a clear enough recording. Years later when people are trying to remember exactly what was said or done (particularly if some or all of the participants are no longer around), even a noisy, mono cassette recording with a poorly-placed, third-rate microphone is something to be immensely grateful for.

--best regards
« Last Edit: April 16, 2018, 05:45:35 PM by DSatz »
music > microphones > a recorder of some sort

Offline kuba e

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Re: Best Mic for Lectures?
« Reply #6 on: April 16, 2018, 01:26:03 PM »
Thank you for nice explanation. This is helping to clarify the principles. I agree, recording the lectures in stereo has better results, it is more pleasant to listen. A minor disadvantage is when the lecturer moves to the side and you have no possibility to angle mics.  But the stereo image can be centered in post processing. Or, we can use only one channel of stereo as mono recording, then all will be in the center.

 

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