Recording Audio

Even as a DP you'll need to know a bit about recording audio and how these two crafts will merge. Ultimately the sound mixers audio will have to sync to the picture you're shooting, so its important you have a good understanding of the total process.

Frame rates must be confirmed between the sound mixer and the DP. Sound can be recorded at different frame rates and it will also affect how the timecode is produced, so its important that these two sync up.

The following are ways to sync the audio:

Timecode

Timecode is the professional standard for syncing audio to picture. You will always be trying to make sure you have the ability to do a timecode sync to camera.

Timecode is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Usually this timing synchronization system is built into the sound recorder or is an external timecode generator. The sound mixer will give you a timecode box that can then be plugged into your camera. This can either be into a Timecode in/out port, or it can be into an audio channel, as time code can be transmitted as an audio signal as well as a digital signal.

Hop

A hop is an output of the sound mixers final mixed down track that is recorded directly into the camera. It is usually a wireless transmitter from the mixer to the camera, but can sometimes be a wire run from the mixer to the audio ports of the camera. You'll find the wired version more often in interview type setups, since the camera is less likely to move.

This can be great for post, but not the best for the sound mixer. The post team will get the video files with sound already synced to it, but often times they won't sync back to the original recorded files from the mixer. This can lead to a poor quality recording being used in the final edit. Sound mixers will vary in opinion if they prefer to use a hop or just timecode only, but most will provide a hop if asked.

In order to provide you with a Hop you will need to make sure you have an XLR input to your camera. For example on the Alexa Mini you'll need something like the A-Box as it has a proprietary connection for audio input. The A-box however will convert that audio input into a standard XLR plug.

Scratch Track

This is dependent on the camera you use as most higher end cameras such as the Alexa Mini do not have sound recording options. Cameras that are meant more for documentary type work such as the FX6 or the C500, will have a built in microphone that can be used as a scratch track. As long as this mic is recording it can be used either manually or in conjunction with audio syncing software to match up the waveforms. A scratch track is the cheapest way to sync for a music video.

Phantom Powered Microphones

Microphones require power in some way. If a microphone requires phantom power, then your camera will need to be able to power it. Again cameras that are meant to shoot documentaries can provide phantom power, but cinema type cameras like the Alexa Mini do not provide phantom power. Instead you'll need a microphone with a built in battery or that accepts AA or AAA batteries.

Alternatively you can use a pre-amp or another device that is powered and can provide phantom power to your microphone.

If your microphone does not receive power as needed it will not work.

Mic Level Vs. Line Level

Some cameras such as the Alexa Mini and Alexa Mini LF can only accept line level audio. Line level audio has a much higher signal level than a microphone output and is usually sent from a sound recordist's mixer after the mic channels have been amplified.

Mounting an on-camera microphone and plugging it directly into the camera isn't possible on the Mini or Mini LF because the microphone's signal level is so low that the camera can't register it. Instead, the microphone needs to go through a device that can amplify the signal from microphone level to line level.

You can use the Mini Papi Pre-Amp in order to amplify the levels to a level that the Mini expects.

Slate

Depending on if you use a smart slate with timecode displayed, or a dumb slate with no timecode, it can still be a useful syncing tool. Clapped at the head of each take, it will give the editor a point at which they can line up the sound of the clap with the picture of the moment it claps. If it has timecode and they are having issues syncing, they will also be able to figure out the offset of any timecode issues quickly and easily.