When I consult podcasters that want to use 2 or mor microphones for podcasting, I recommend a mixer like the Alesis MultiMix 8. Sometimes the podcaster doesn’t want to deal with anything more than what a USB mic has to offer. So they ask if you can connect more than one USB mic to your computer to record.
The answer is you can with a little bit of work at the beginning
How USB Microphones Work
Normally by plugging in a USB microphone you are turning that sound device into the primary. The secondary or tertiary sound source is not the default, but can be used.
16 bit vs 24 bit sound card
I covered this in the article on Cheap microphones vs. expensive. The important part is when you use multiple USB mics they all need to be at the same bitrate as the others. Its not that you cannot try using different rates but that could cause problems in the recordings. Its best to have all USB microphones at the same bitrate (most USB mic are at 16 bit but higher end ones can bump up to 24 bit).
It also depends on the computer. 24 bit mics use more resource because they are collecting more data. If you put 2-3 USB microphones into the mix, the computer might have problems keeping up or one mic might show latency over the other.
One thing to point out: Right now I am saying “Microphone” but a USB device can also be a mixer – like the M-Audio or Edirol mixers I talked about in an earlier post. The original soundcard can also be incorporated into this process.
Which Audio Programs Can Use Multiple USB Microphones?
Even though you can connect microphones, you might not be able to use them on your program. It seems that any program that can do a multitrack record are able to record multiple USB mics. Each mic will end up taking a single channel. If you have a stereo mix then one mic will be on the left channel and one on the right.
Garageband, Adobe Audition, Audacity, Sony Acid, Cubase are some of the programs that will let you set up multiple track recording.
How to Set Up Multiple Mics for Use in Podcast – Mac
Keep in mind, this is Mac OS X Mountain Lion. Earlier versions settings will be slightly different. Open up the Audio MIDI Setup (In Go > Utilities > Audio MIDI Setup). You will see your input and output devices.
Plug in your USB mic and you will see it show up in this panel. The microphone can take up more than one input and output channel. That is how USB mixers will work – they could take 3-4 channels (or more) for input and output. You can then multi-record.
Here is where the magic comes in:
On the bottom left – choose the + - then Create Aggregate Device (this may be in the preferences if you have an older version of OS X). A Blue plus will show up. when you select that device, you will get checkboxes on the right. Choose all your mics you want to use.
You can setup input and output devices. Keep in mind – the maximum number of input/output devices for USB is 127 (this is the limitation of the USB bus). I would guess you could go past that if you used Firewire or Thunderbolt audio devices. I am guessing 127 USB mics will take up too much resources and freeze your computer.
Drift Correction – What is it?
If the two sound devices have different sample rates, then you check drift correction so they align properly. Since most USB microphones work on the same rates, the boxes should be unchecked. If the box is checked once you add the device, make sure of its sample rate and try to match with your other devices.
How to Set Up Multiple Mics for Use in Podcast – Windows
Windows does not have a direct option. There is some software out there that will allow you to use 2 or more audio devices as one. Virtual Audio Cable is software by Eugene Muzychenko. The software is $25 (with a free trial). You can use it with multiple software including Audacity and Adobe Audition.
Can I Setup Multiple USB Mics on an iPad-iPhone-iPod?
Lets put it this way – there is a 5 in 1 connector for iPad out there. This shows iPad has the ability to run more than one device at one time through the lightning port. However, the software would have to recognize there is more than one audio channel for this to work.
There is a solution out there – the Alesis IO Mix is a 4 channel audio mixer for iPad. You can connect up to 4 channels to record.
Out of all the options, Mac is the best to use multiple USB microphones. However, if you are planning to record more than two voices at one time, it might be better to get a mixer (usually around $100). The USB out in most mixers will allow you to record multiple separate tracks or record as one track.