Field Audio Recorder Product

Overview

Field audio recorders capture synchronized high-quality sound for video productions on location. Unlike consumer audio interfaces, professional field recorders are engineered to deliver broadcast-grade audio quality, timecode synchronization with cameras, and rugged construction for outdoor environments. This model emphasizes dual-channel recording with a small footprint, making it suitable for documentary, interview, and ENG (Electronic News Gathering) applications.

The recorder combines low-noise microphone preamps (Microphone Preamp Stage), high-resolution audio conversion (Audio AD Converter), and professional timecode I/O (Timecode Module) into a pocket-sized form factor. Dual SD card slots enable redundant recording, ensuring no audio is lost if one card fails or is full.

Recording Signal Path

Audio enters via XLR combo connectors on the front panel. The Microphone Preamp Stage dual-channel preamp accepts balanced microphone signals, with switchable 48V phantom power for condenser microphones. The preamp provides up to 60 dB of gain, sufficient for quiet lavalier mics at a distance.

The preamped signal flows to the Audio AD Converter, which samples the audio at 96 kHz with 24-bit resolution. This high resolution (versus standard 16-bit CD audio) preserves headroom and allows for greater dynamic range in post-production. The AD converter feeds I2S digital audio into the Audio DSP.

The DSP module performs real-time metering, mixing, and optional compression/EQ. The final stereo audio stream is written to both SD cards simultaneously via the Media Storage, providing instant backup. Recording rates up to 192 kbps (24-bit 96 kHz) allow 10+ hours per 64 GB SD card.

Timecode Synchronization

Professional video production requires audio and video to be locked to a common timecode clock. The Timecode Module accepts LTC (Linear Timecode) input from the camera via a BNC connector. The timecode is embedded as metadata in the audio file and displayed on the LCD Display Module.

During post-production, the editor synchronizes video and audio by matching timecode. A camera rolling at 24p and the audio recorder both stamped with the same timecode means the editor can auto-sync across multiple cameras and sound devices with frame-accurate precision. The recorder can also slave its internal clock to incoming timecode, ensuring it stays locked to the camera master clock.

Power and Runtime

The Power and Battery uses four AA NiMH cells, delivering 4.8V nominal. Internal 5V Buck Converter and 12V Boost Converter converters generate the 5V logic rail and 12V phantom power rail. At a typical consumption of 400 mA (preamps + DSP + display), four AA cells (2500 mAh nominal) yield 6–8 hours of runtime. Paired with spare batteries on set, a 10–12 hour shooting day is easily supported.

Micro USB charging (via USB Charger Module) allows on-set charging via portable battery packs or USB hubs during meal breaks.

Mechanical Design

The Main Chassis aluminum extrusion provides RF shielding and impact protection. Shock Mount Set elastomer isolators decouple internal circuits from vibration, reducing mechanical noise coupling into audio paths. The recorder easily fits in a camera bag side pocket or clips to a boom pole mounting bracket.

The Front Panel Faceplate XLR jacks are recessed into the housing, protecting them from impact and spilled liquid. The rear Rear Panel provides access to the SD card slots and battery compartment.

Monitoring and Metering

The LCD Display Module shows real-time recording levels, timecode, battery status, and SD card space remaining. Eight LED indicators per channel provide instant peak metering. A stereo headphone output (mini-jack) allows the boom operator to monitor live audio during recording, critical for catching mic brushing, wind noise, or talent clipping.

Typical Workflow

On-Set Timecode Sync: The camera (e.g., Sony FX9) transmits LTC timecode over BNC to the audio recorder. The recorder locks to this timecode and begins recording. When the camera rolls, both devices are stamped with identical timecode. Post-production auto-sync matches video and audio in seconds.

Dual-Channel Interview: Two lavalier mics are plugged into channels 1 and 2. The preamps are set to −12 dB and −10 dB respectively (accounting for different mic output levels). Both channels are recorded to both SD cards. If one card fails, the backup card contains the full interview stereo mix.

ENG Documentary: A single wireless lavalier receiver output feeds channel 1. A boom mic feeds channel 2. The recorder tracks both simultaneously, allowing the editor to switch between close-mic'd talent (lavalier) and ambient environment (boom) during editing.

Noise Performance

The Preamp IC Channel 1 and Preamp IC Channel 2 OPA2134 operational amplifiers are chosen for extremely low noise: 1.2 nV/√Hz spectral density. With 60 dB gain, the input-referred noise is approximately −130 dBu, allowing sensitive microphones (like lavalier condensers) to be recorded with minimal self-noise degradation.

The Anti-Alias Filter 40 kHz low-pass filter before the AD converter removes ultrasonic content and RF interference, preventing aliasing artifacts. Wind noise and RF interference are handled by careful grounding and shielding in the preamp stage.

Limitations and Alternatives

The dual SD slot architecture assumes simultaneous recording to both cards. Some workflows require splitting channels across cards (Channel 1 on Card A, Channel 2 on Card B) for faster offload and transfer. Firmware can support this, but it reduces redundancy.

The recorder is passive: it does not generate timecode independently. It requires an external timecode source (camera or master clock). Standalone timecode generation requires an additional module or separate device (see Timecode Sync Box).

The stereo monitor output is limited to mini-jack; professional monitoring workflows often use XLR. An external headphone amplifier can be connected via the mini-jack for higher professional headphone impedances.

Extreme cold (below −10°C) slows AA NiMH discharge and reduces phantom power supply stability. Arctic expeditions use external lithium batteries or AC power tents.