Know your microphones
Omni – all directions
cardiod – hears front, side rejection and small sensitivity bubble in back.
Super cardiod – more narrow front, large side rejection, medium sensitivity bubble in back
Hyper cardiod – Even more narrow in front, larger rejection in side, larger bubble of sensitivity behind mic
Shotgun – Super narrow front, small bubbles on sides and back – best for side rejection, even with small sensitivity bubbles on sides.
Proximity Effect – The closer you get to your mic, the higher the bass response. After 8 – 14in away from source, proximity effect is reduced.
On Axis / Off Axis – Describes how mic is directed towards sound source. Positioning mic on axis (pointed directly at source) is critical to capture all frequencies from sound source.
Lower frequencies are less directional and have more energy, so directional mics have a wider pickup spectrums for lower frequencies. To accurately capture higher frequencies, you must have mic pointed directly at source.
Any long barrel microphone with narrow acceptance patterns. Only long, long microphones actually have that narrow, front only pattern. Smaller ones uses interference tubes on unidirectional mics, using wave cancellation to reduce frequencies from the side. They are more super – hyper cardiod than shotgun
Shotgun mics have higher sensitivity, leading to a higher output. This doesn’t necessarily make a mic better than another. High sensitivity mics are used for lower signals, so anything lound can be distorted.
Knowing the sensitivity of your mics informs their distance from the subject. and knowing their field of sensitivity informs how they are arranged on the set.
Watch out for the mics self noise (hiss
D). This is the sound of the circuitry in the mic, so you want the lowest self-noise level you can get. You want below 15dbA noise level.
Using a battery in the shotgun usually creates more self noise and less sensitivity than using phantom power for the mic.
Look for mics that have XLR connections
You don’t have to use shotguns for your filming. Dynamic mics are reliable and cheaper, they also have off-axis sound rejection. They have lower sensitivity as compared to condencers. Watch out for proximity effect, depending on the polar pattern.
Condensers have lighter diaphragms, allowing them to respond faster, giving more accurate audio records. They aren’t as resilient to shocks and temperature / humidity changes. They also have a higher sensitivity than dynamics.
Pencil condensers are great for interviews because they are small and often have super cardiod patterns. Must get mic close to source. Look for 15mv of sensitivity.
Mics with high sensitivity are valuable when using records with weaker preamps. As you raise preamp gain, you increase noise. It is similar to increasing ISO. I wonder if there is a photography metaphor with audio recording?
These are small mics that allow for hands free operation. They come with clips and the cord is run to a transmitter or sent to a recorder. You get good signal to noise because mic can be placed close to source.
Hiding the mic can reduce the frequency response. It isn’t always necessary to hide, for example, in interviews you are able to show mic and clip, but hide cord.
Watch for when you need to position mic, don’t want to make subject uncomfortable. Also make sure the mic looks good and isn’t distracting. Try to keep 8 inches away from mouth, and located where it wont get ots of clothes rustling. For lav mics, they will have higher self noise, so try to get under 30dbA.
Wireless systems that don’t cost a ton aren’t very useful. It is best to use wired systems unless they are necessary.
Recording Your Audio
Don’t use your camera, so try to use dual system audio. You’ll want XLR inputs, phantom power, clean preamps, and headphone monitoring. It’s also nice to have an audio output.
To get best performance from audio recorders, you need mic that have a high sensitivity. Another option is to use a mixer to pick up the signal and do some signal modeling before you send it into the audio recorder.
Use closed, over the ear headphones. Or use the noise-isolation inner ear type of earphones. YOu want a flat frequency response
Setting Up Your Mics
You can use pencil condencers as boom mic, on a boom pole pointed towards mouth. They won’t be as powerful as your shotgun, but they can have a nice presence and sound. When recording, shoot for -10dB peaks.
When using wired lavs, want to make small loop at attachment point so the mic itself doesn’t get stress should the cord get tugged. You want to put it 8 inches down from mouth, in center of chest.
How To Make Your Interview Sound Great
First, you will need to sync your dual system audio files, but thankfully Premeir Pro makes this simple. Remember, if you use a clapper or anything to sync the audio recorders, you can simplify this process even further.
Of course, computers are smart enough to use audio files and sync them with the audio files.
You have to consider the distance between the subject and camera, so if camera is a good distance away, you will have more trouble in syncing the camera.
Once you have the audio sync’d, cut them and align the files, the unlink the original audio and link your main clip to the good audio clip.
Once you have your good audio clip tied to your video clip, right click on the audio to adjust the audio gain. You can then normalize your audio to -3.
Handling Room Noise
If you get some reverb, try these steps:
- Set low cut EQ at 50Hz
- Sweep to find resonant tones picked up by mic, try to find anything that is ringing.
- Put a limiter on the master bus to keep audio from passing 0dB
- Gain a bit at the high end to add presence
- For interviews, shoot for subtle amount of compression, around 4dB.
- Raise the gain to whatever the amount is being compressed.
- Expanders are basically backward compressors, when audio is below threshold, rather than cutting it out like a gate, it lowers it by the given ratio.
- Expanders are great at cleaning up ambient noise like room reverb
- start with a ratio of 4
Mixing the Interview with Background Music
You want to be able to hear the interview clearly above the music beneath, but you also want to be able to hear the music, so you need balance.
Listen to your mixes both quiestly and loudly. Vocal fidelity will be around 2k to 3k, so bring down other audio sources in that range to make room.
Try to mix the main speaking portion