FAQ: Microphones

Microphones

What microphone should I use with my minidisc?

There is no one answer for everyone. For more details, check out the transom tools What Microphone Do I Get? column, but the main decisions are these: omni or directional, dynamic or condenser, handheld or lavalier, mono or stereo?

There are a few additional challenges when using a small consumer digital recorder, as the mic input is a high-impedence 1/8 “mini connector,” while most pro microphones are low-impedence with XLR connectors. Get a high-quality converter cable, wired for this purpose, with an 1/8 ” mono connector on the recorder end if you are using a single mono microphone. It may be worthwhile to get a cable that adapts from XLR to mini and also adjusts the impedence and shunts the plug-in power. The Shure Shure A96F does all of these things.

Which Pick-up pattern?

Omnidirectional mics pick-up sound from all directions equally, while directional mics pick-up best in a limited zone, usually in front of where you aim the mic. An omni mic is more forgiving of imperfect placement, and will sound more natural if the source is not directly in front of the mic. Omnis are also less succeptible to handling noise, wind and p-pops.

Directional mics give a tighter, more focused sound, and will record less of the surrounding ambience, which can be good or bad depending on your intent. There are degrees of directionality, from the cardioid, a fairly wide pattern that is very practical for close-up interviews, to the shotgun, which has a very narrow angle of sensitivity, best suited for more distant applications. In-between are hypercardioids and short-shotguns. As directionality increases, handling, wind and breath noise become more of a problem, and off-axis sounds seem increasingly unnatural.

For field recording and ENG (electronic news gathering) the most popular omni mics are the Electro-Voice RE50B and the Beyerdynamic M58.

The most-used cardioid mic is the Shure SM58. Shotgun mics by Audio-Technica and by Sennheiser are frequent choices.

Dynamic or Condenser?

Dynamic mics are more durable, can handle higher sound pressure levels, and require no additional power.

Condenser mics have a louder output and can pick-up more subtle details, but require phantom power. That power can be provided by some recorders, a mixer, an external device, or sometimes an internal battery. Many of the small consumer minidiscs have something called “plug-in power ” which is similar to phantom power, but cannot power professional mics. It provides power for electret mics designed to be used with these recorders.

Handheld or Lavalier?

In most cases you will get better sound quality with a handheld microphone. Lavaliers are not placed in an ideal position and often pick up clothes-rustle. But there are circumstances, such as an intimate conversation where an obvious mic would interfere with the feel of the interview, or a subject moving in such a way that keeping him or her “on-mic” would be impossible, where a lav can save the day. But with the up-close feel of current radio styles, lavs can often sound distant or muddy.

Mono or Stereo?

Stereo sound can add a lot to the vividness of your location recordings, but can be quite distracting during interviews. So you may want a stereo mic for ambience and demos and a mono mic for interviews. See the Transom: Stereo-Types column for details on techniques and two-mic arrays.

The inexpensive stereo mics that are sold to go with consumer digital recorders can get decent sound, and may be more than sufficient to get some backgrounds for your piece, but they are not particularly durable, often made of plastic, and have limited bandwidth, reducing high-frequency detail. Better choices are the relatively inexpensive Audio-Technica AT8022, the Rode NT4, or the Shure VP88.

Why Can’t I Get Enough Volume From My Mic?

Some users have reported problems getting enough level into their digital recorders. Make sure you are manually setting the record level, the automatic gain control rarely sounds good.

If you have the record input level turned up all the way and you still aren’t getting enough level, you have a few options:

  • Make sure you have a good quality cable, not a pieced-together series of adapters and mis-matched connectors.
  • If you’re using a dynamic mic, you may want to try a condenser instead, they almost always have a louder output.Condenser mics require phantom power, so be sure to pick one that can use an internal battery, unless you have an external source. A consumer digital recorder’s “plug-in power ” will not power a pro mic.
  • Another volume-increasing tactic is to use an impedance transformer. The 1/8 ” connectors on small minidisc machines are high impedence, while pro mics with XLR connectors are almost always low impedance. You actually don’t want the impedences to match exactly, but raising the impedance a bit can give you a few more dB of volume. A cable like the Shure A96F will do both things: convert your XLR to a mini and raise the impedance enough to give a bit more volume.

What’s plug-in-power, and is it creating noise on my mic?

Plug-in-power is a small voltage delivered from the recorder to certain electret microphones, it’s similar to phantom power, but the two are not interchangeable. You can’t power a standard condenser mic with plug-in-power, nor can you run a plug-in-power mic from the standard phantom power often delivered by pro recorders or mixers.

So the deal is that if you buy a small consumer level mic, some of which are pretty good, like the Sony stereo mics, or the (discontinued) little Radio Shack lavaliers, you can plug them straight into your minidisc and they’ll get the required power from the deck. Otherwise you’d need to use an adapter with a battery.

If you want to use a dynamic mic, such as the EV RE50, or the Beyer M-58, don’t worry about the plug-in power, you can ignore it, although the Shure A96F will give you better volume, convert the connector types and shunt the plug-in-power.

If you use a pro condenser mic that needs phantom power, you’ll need to get one that can use an internal battery, or get an external phantom power supply: the plug-in-power will NOT power a pro condenser mic.

There have been occasional reports about “plug-in power” (a small voltage carried on the mic cable, provided by many consumer digital recorders that can supply a needed charge to some electret microphones) creating clicks or noise when using a dynamic microphone. I’ve never found the plug-in power to create any problem; dynamic mics generally don’t react to it. If you get hiss from your mic, it’s most likely just from the relatively weak preamps that were designed to work with high-impedance electret mics that do make use of the plug-in power. Crackles are more likely due to a bad cable or dirty or worn jacks.

So, as we’ve discussed a few times on this site, the Shure A96F will raise the impedance a bit, which will give some more gain, it also shunts-off plug-in power if you’re concerned about it, and it’s a nice simple XLR-to-mini cable with the transformer built-into the XLR jack, so it’s not a kludgey pile of connectors.

I have one mic, am I recording in stereo?

It depends on your mic and cable. Most conventional interview mics are mono, in that they only produce one channel of sound. Often one connects a cable from that mic to the recorder that is wired to send that same signal to both the left and right channels of the tape or disc. This is often preferable to only hearing the microphone in one ear while monitoring the recording, but it doesn’t make it “stereo,” there’s just an exact copy of the signal on both channels.

It’s easy enough to record just one channel and pan it to the center during your mix, or copy one signal to both left and right if that’s easier. In fact, when transferring audio to the computer, it will save disc space to only record one channel onto your hard disc if the sound is not stereo.

“Stereo” is most commonly used to describe two tracks of audio, a left channel and a right channel, which are meant to represent a spacial orientation analogous to how our ears hear. Stereo recordings can be made with two microphones, or with a stereo mic that has two mic elements in one housing. Depending on the recorder’s input, the signals from the two mics or mic elements can be carried on two cables, or a single cable.

A similar recording technique using two mics (or other inputs) which is not truly “stereo ” is “two-track” recording, basically using your stereo recorder as a small multitrack machine. One can record two completely separate sounds, one on each channel, to be manipulated later in the production process. One could have one mic for an interviewer and another for the interviewee, each routed to its own track. One could use both a lavalier and a hand-held mic to record the same source, routing each mic to its own channel, so one could choose between the sounds, or combine them, later. If recording interviews or other sources that can be in mono, even complex multi-mic recordings are often more useable later in production if half the mics are routed fully left and the other half fully right, just to reduce the number of “live” mics on any one channel.

I only have one cable, how can it be carrying stereo sound?

Cabling can be very confusing, because the same types of wires and connectors can be used in very different ways.

In the analog realm, one usually needs one cable for each channel of audio, so connecting most gear will require a cable for the right channel and a cable for the left. RCA cables and 1/4-inch “TS” cables that have a single ring on the jack, handle only one channel of audio.

But for the sake of saving space, small portable recorders, laptops and a few other devices use stereo inputs or outputs on a single jack.

In that case, one can use one cable to transfer stereo audio, as long as it is a three-conductor cable with the correct “TRS” connectors on the ends. TRS stands for “Tip-Ring-Sleeve” for the three conductors on the plugs. You’ll see two black bands on the plugs, one near the tip, another ring about midway down, and the long sleeve of the shaft is a conductor as well. 1/8-inch or “mini” TRS cables are commonly used for connecting the stereo headphone output of a small minidisc recorder to the stereo mic input on a computer. Some stereo mics use a mini TRS (often just called a “stereo mini”) plug to connect to the mic inputs of a minidisc or a small portable DAT recorder.

One may need adapter cables to interface a device that uses a stereo input or output with a mixer, or audio interface. For instance, to connect a portable minidisc to an audio interface like the M-Box, one needs a cable with a mini TRS on one end, and two 1/4-inch cables on the other. Plug the mini TRS into the headphone out of the minidisc, and the 1/4-inch cables into separate left and right inputs of the interface.

Even professional mono mics often use an adapter cable that terminates in a mini TRS plug, in this case because there’s only one channel of audio coming from the mic, the cable should bee wired to send the audio to both the tip and ring.

There are 1/4″ TRS cables which are more often used for carrying mono “balanced” audio. A headphones cable is of the few wires that uses 1/4″ TRS to send stereo audio, more often those three connectors are used to “balance” a mono signal. The one common exception is an “insert” cable that uses a 1/4″ TRS to move two channels of audio, a “send” and “receive” channel to an external processor. These cables usually have a 1/4″ TRS connector on one end and two (mono) 1/4″ TS connectors on the other.

In the digital realm, a single digital connector cable usually transmits two channels of audio. It’s confusing because the cables look the same as ones you’d use for analog audio (although you should try to use cables designated for digital audio, they have specific impedance ratings that are optimized for transmitting digital signals.)

The S/PDIF standard uses one RCA cable to send stereo audio along with other info between devices. AES/EBU uses a single XLR cable to send stereo audio. The two standards are similar, but one cannot just use adapters to connect an RCA S/PDIF output to an AES/EBU XLR input. (Some have reported success doing that, but it’s unreliable). One can buy converter boxes that will maintain proper cable impedance if one needs to interface S/PDIF and AES/EBU devices.

There’s also an optical S/PDIF standard that sends stereo signal down an optical cable with small square-ish plugs on each end. Consumer minidisc recorders often use an optical digital connection, but in most cases that connection is just an input, and might require a special cable to attack to the special small optical input on the minidisc.

Devices using RCA, or “coax,” S/PDIF can’t be connected to devices using the optical S/PDIF standard without a special converter box.