One of the biggest questions facing amateur videographers is whether or not they need to invest in an external microphone. Believe it or not, my advice can go either way depending on the camera and the situation. Onboard microphones generally perform poorly, but it can be good enough if you have the right camera and are filming in the right environments.
It all comes down to what you have and how you want to use it. External microphones can be quite cumbersome in most environments, turning a pocketable device into one you have to either keep in a special bag or hang over your shoulder when you’re not using it. There’s really no point in buying an expensive external microphone if you don’t really need one.
For example, an iPhone’s microphone is generally quite good, especially for subjects that are an arm’s-length away from the camera. You might run into trouble when you’re in a crowded environment with a high noise profile, but this could be equally bad for most external shotgun and/or omnidirectional microphones.
A good microphone is only one piece in a greater chain of audio quality. You can do a lot with good audio editing software, and setting the right levels will dramatically improve the noise presence in a track recorded with an onboard setup. Often, users will set their audio levels to the point where their words appear in red on the meter with the idea in mind that they can always reduce it in post. This introduces audio distortion which actually can’t be filtered out without degrading the clarity of the speaker.
A lot of onboard microphones tend to exist within reach of the user’s fingers. That is, a slight variation in how you’re holding the camera can muffle or mute the speaker. You may not have any clear indication that this is happening apart from jumps in the audio meter as you slide your finger across the microphone. Additionally, these microphones tend to be poorly isolated from the device’s exterior. If you tap anywhere on the device itself, this will come across as a bump or spike in the audio levels. It’s annoying, and can ruin a perfectly good production.
Reference Microphones Should Not Be Used in Production
People run into problems when they attempt to use a microphone that’s designed for reference rather than production. Reference microphones are most commonly found on DSLR cameras and are intended simply to allow a video editor to align audio tracks from multiple sources with the video. This is how it’s designed, and anyone considering shooting video with a DSLR should realize this.
I’m generally of the opinion that external microphones are necessary for commercial video production, but optional if your onboard mic does a good enough job for you. A $200 external microphone is a waste if you don’t really need it.