Although the Arri Alexa Mini LF audio interface is heavily stripped back compared to other cameras, there are still some great options for recording audio to camera. The Alexa Mini LF can record up to four channels of linear PCM (24bit, 48kHZ) audio. Each channel is linked to either the 6-pin Lemo audio input or the internal microphones.
|6pin Lemo Audio Input||Channel 1|
|6pin Lemo Audio Input||Channel 2|
|Left Internal Microphone||Channel 3|
|Right Internal Microphone||Channel 4|
Audio Input Level
The Mini LF allows you to input line level audio into the camera. Line level audio has a much higher signal level than a microphone output and so 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 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.
Our go-to device for doing this mic to line level conversion is the Sound Devices MixPre-D. This device is (relatively) compact and has high quality preamps that are perfect for taking the low level signal from microphones and amplifying them to line level without introducing excess noise.
The camera's audio input is through a 6-pin Lemo plug on the back of the camera. Four of the pins are used to input 2 separate line level audio inputs into the camera. The other 2 pins output 12v which can be used to power your preamplifier or wireless audio receiver when used with the appropriate cable.
This 6-pin connector is pretty new in the industry and because most people are still using the good old 3-pin XLR cable, we include a Wooden Camera A-Box in our LF kit to convert the 6-pin Lemo and allow you to use the more familiar XLR inputs.
The super 35 Alexa Mini has the same 2 channel line level input as the Mini LF, but there has always one major problem. When you just need simple "scratch track" audio for reference in your edit, the only way to get it is by using the previously described method of running through a mic to line level converter. However, that can give you a real headache if you don't have room for mounting extra accessories - for example, if you are using the camera on a gimbal.
Arri have addressed this issue in the LF version of the Alexa Mini and have integrated 2x built in microphones for recording reference audio. The recording level on these internal microphones is fixed, with the left microphone (channel 3) using a +18dB higher gain than the right microphone (channel 4). This is to cover a larger range of audio levels.
Enabling Audio Recording
By default you will need to turn on the audio recording option in the Mini LF's menu. Navigate to the recording menu, then scroll down to the bottom to enter the recording menu. Here you can activate audio recording by ticking the box. You can also turn on the internal microphones for recording a scratch track in this menu.
One thing to remember is that the audio from both the audio in connector and the internal microphones can only be recorded at frame rates that match the project rates. These are 23.976 fps, 24 fps, 25 fps, 29.97 fps, 30 fps, 48 fps, 50 fps, 59.94 fps and 60 fps.