A beginners guide on how audio and the MixPre 3 work.
Definitions
Mono: one channel being recorded, so the left and right channel are the same
Stereo: multiple channels being recorded so that the left and right channel can differ
Gain: the amplification level of an audio signal
Phantom Power: DC current being sent to the microphone through the sound device
Preamp: makes a weak signal into an output signal strong enough to be recorded
Bus: carries a signal from one place to another down the line
Mixdown: a mix of all channels being recorded, usually shows up as a L/R signal
Sample Rate: rate at which the audio is recorded, we tend to use 48kHz
Plosives: hard sounds such as “p” that distort
Transient: spikes/peaks in sound
Single Process Sound: sound is recorded through the camera
Dual Process Sound: sound is recorded using a separate audio package
Types of Microphones & Pick Up Patterns
Dynamic– more durable, no phantom power needed
Condenser– phantom power needed, sensitive to loud sources so they are not as durable. Waterfalls and high vibrations will break the mic
Omni-Directional– picks up sound all around the microphone
Bi-Directional/ Figure Eight– picks up sound from the front and back of the microphone
Cardioid– picks up sound from the front of the microphone
Hyper Cardioid– picks up sound from the front in a narrower pattern than a cardioid microphone
Shotgun– highly directional, picks up sound best in the front but is able to pick up noise on the side and back as well
Which Microphone to Use
Shotguns are used the most for picking up dialogue thanks to their directional pick up pattern
Diaphragm condenser mics (SM7b, Neumann), and shotgun mics are good for VO work due to their pick-up pattern and quality. All have a good low-end frequency range.
Diaphragm Sizing: if the capsule size is less than 1” it is small, if it is 1” or more then it is large Small: able to respond quickly and easily to sound, peaks are harder on these types of mics, can help with folly
Large: with the extra mass it is not able to pick up sound as quickly/sharply as the small, often gives a smoother sound as is used with voices
Lavalieres are mainly used for interviews, news, etc
Bi-Directional Mics (MXL 990) are used in most musical productions in order to pick up sound from both the front and back
Direction box/DI Box/Direct Boxes take instrument inputs and makes them microphone outputs. These can also be used with computer signals.
Boundary mics/PZM are used to pick up location noises, movement through a space as they are flat and pick up the noise as it hits the flat surface. Easy to hide in a space as the bottom is flat
Proper Microphone Placement
You want to get the mic as close to the source as possible for proper audio recording, 12-18” away from your actor will help
- Remember to keep the placement distance of the source to mic consistent. This will aid in keeping audio levels and recordings similar from shot to shot.
When you can go top down with the shotgun, as this will pick up the source better. Going down up can give bad distortion especially with plosives as you have taken it off axis. There can also be a slight time delay when pointing down up.
Only use omni directional if you are in a well acoustically treated space, like the whisper room. Lav placement can depend on whether or not you want it seen, if it can be seen then mount it on the lapel. If you need to hide it use the cone trick with gaff tape and place it on their shirt or their chest/sternum.
What We Hear & Room Tone
Everyone hears differently, microphones pick up all sources in the location
- Example: when someone is talking in studio 5 you don’t hear the fans from the lights, when we stop talking, they become noticeable. Microphones pick up the noise of the fans as well as the dialogue.
Be sure to record the room (or other shooting location) with nothing happening for at least 30 seconds
- This sample of ambience can be used to fill gaps or help “dirty up” takes in which the audio sounds unnatural or is disrupted by clothing noise, etc.
Levels & Meters
Dialogue should be between -20 to -12 anything more and it is considered peaking and will be distorted.
When setting levels ensure that the talent is speaking at the volume that they will be at during filming
Set the preamp gain levels first as the larger knobs on mixers tend to be for the bus audio levels
Our ears squash loud noises that spike on the meter, which is why you want proper levels for recording and proper headphone volume.
- To set your headphone volume turn on tone or pink noise, if you have it available, and set the headphone levels just below unbearable. This will allow you to easily identify when your recording levels are too low or high.
Download: Introduction to Audio