The A20-Mini wireless microphone transmitter is the industry’s first and only transmitter which features built-in 32-bit floating point recording. This is very significant: with 32-bit float recorded files, audio gain decisions can be fully made after recording. This may sound provocative to an experienced sound engineer. Prior to 32-bit float recordings, the recorder’s microphone preamp gain needed to be set optimally before or while recording–high enough to overcome electronic noise of the recorder, yet not too high that clipping occurs with loud sounds. 32-bit float changes all of that.
Although this sounds like magic, it is not — it is pure science. Four distinct subsystems are required for 32-bit float operation. These are:
- A very high-dynamic-range analog microphone preamplifier
- Multi-stage A/D converters
- 32-bit float internal processing
- 32-bit float WAV recording file format
The analog microphone preamplifier in the A20-Mini transmitter/recorder has >130 dB of dynamic range. This allows the input to capture the entire dynamic range of any lavalier microphone connected to the A20-Mini. This custom-designed circuitry, taking advantage of the latest FET and bipolar amplifier developments, result in the lowest noise and distortion possible. The preamplifier is so quiet that connected microphones will always generate more noise than the preamplifier itself. While having very low self-noise, the preamp has also been designed to simultaneously have very high headroom to feed the A/D converters.
Multi-Stage A/D Converter
The analog-to-digital converter is one of the most important stages in a digital recorder – this is where the analog sound gets converted into a digital bitstream. The best audio A/D converters presently on the market yield roughly 130 dB of dynamic range and consume a lot of power doing so1. Sound Devices patented a method of combining multiple fixed point 32-bit A/D converters. This unique combination results in an A/D conversion stage which yields over 130 dB of dynamic range while consuming very little power. The output of this stage of the hardware is 32-bit floating point audio data.
32-Bit Float Processing
It is worth reviewing the technical article on the math behind 32-bit floating point. The important point to remember is that 32-bit floating point processing of audio signals exceeds 1500 dB of dynamic range, so virtually any amount of gain can be added to or subtracted from the signal. This is not to say that the analog audio circuitry itself has 1500 dB of dynamic range, but rather that the internal signal path and processing has 1500 dB of latitude — the 130 dB of dynamic range of the actual incoming audio is clearly not impeded. Said another way, it is impossible to clip the incoming signal or bury the signal in the noise floor. All processing within the A20-Mini is performed using 32-bit floating point math.
32-Bit Float WAV Files
The WAV file is a universal container for audio data, capable of storing material in a variety of bit depths, including 24-bit fixed point, 32-bit fixed point, and 32-bit floating point. In order to maintain the benefits of 32-bit floating point audio, audio data must be stored as 32-bit floating point. The audio application which is used to open, edit, and playback the 32-bit float WAV files needs to support this format. While many audio applications do support 32-bit float, support is not yet universal.
32-Bit Float Files In Action
This short video shows an example of an audio file being recorded too hot and then being turned down after recording with a DAW. This video was done using the MixPre series of recorders, but the concept is identical with the A20-Mini.
Since a typical workflow may involve several A20-Minis along with their resultant files, Sound Devices offers the SD-Utility app for batch processing of 32-bit WAV files including the ability to normalize the files and convert them to the more common 24-bit fixed point WAV files.
To be fully useful in a production, 32-bit float recordings need accurate SMPTE timecode synchronization. This synchronization allows the files recorded on the transmitter to be in perfect sync with the picture, as well as all other audio recordings on set. The A20-Mini has a sophisticated high-accuracy SMPTE timecode generator built-in. The timecode generator has an accuracy of 0.2 PPM or better, which means accuracy of closer than one frame per 24 hours. The A20-Mini’s timecode is easy to jam at the beginning of a workday using the Mini’s USB-C port. Accurate timecode is maintained over battery changes due to the supercapacitor-backup power of the generator.
It’s the Hardware
The A20-Mini hardware described above is what enables these units to offer 32-bit floating point audio recordings. Having the massive latitude of 32-bit float audio available for audio processing and storage yields significant benefits. Knowing that the signal from the microphone can never be clipped or recorded too quietly allows the A20-Mini to help the Production Sound Mixer make their job just a touch easier and help make excellent recordings.
1. Based on commercially available analog to digital semiconductors as of July 2021.