GainForward Explained

Picture this: you’ve set your transmitter gain, wired up the cast under their complex outfits, and you’re ready to roll. Unfortunately, in the middle of the first take, one character unexpectedly begins to speak very softly. This didn’t happen during rehearsal! Now you need to quickly pause production, and approach the actor to make adjustments at the transmitter…

With an A20-Mini, this won’t be a problem. Instead of bothering the talent by changing gain at the transmitter, simply make the adjustment right from your 8-Series or A10-RX. This groundbreaking feature is possible with A20-Mini’s GainForward Architecture.

So what is GainForward Architecture? Is it remote control? The answer is no. GainForward allows for real-time adjustment of transmitter gain at the receiver. Unlike systems that use remote control to adjust gain at the transmitter, there is zero lag. And there is never a worry about the transmitter being out of RF range for remote control.

How is it possible that no gain control is needed at the transmitter? Isn’t there a noise or headroom penalty? Again, the answer is no. GainForward architecture differs from systems that require control of gain at the transmitter and which send a limited dynamic range signal over the RF link. Instead, GainForward transmits the entire dynamic range of the analog audio over the RF link and adjustments to gain are done at the receiving end. All analog FM wireless systems and most digital systems require gain control at the transmitter. GainForward systems do not.

Though gain control has been moved from the transmitter to the receiver, audio quality is unchanged. The A20-Mini has the same legendary audio quality as previous Audio Limited products. The A20-Mini contains an incredibly low-noise microphone preamplifier with substantial headroom and over 130 dB of dynamic range.

There are three necessary elements that make the GainForward Architecture possible: 1) a very low-noise microphone preamplifier with significant dynamic range; 2) patented multi-stage ADC (analog-to-digital converter) topology to capture the entire dynamic range of the analog source; 3) floating-point digital RF transmission.

Shown here is the architecture of a typical RF transmitter and receiver used today.

Shown here is the A20/A10 architecture illustrating the three main elements of the GainForward Architecture.

Microphone Preamplifier Design

Audio Limited has been manufacturing very high-end wireless microphone systems since the 1960s. Always a boutique manufacturer, Audio Limited focuses on a “money is no object” design philosophy and produces incredible-sounding products like the 2040 system and the A10 Digital system. Famous for their audio quality, these products have been used on high-end feature films for decades. 

The A20-Mini carries on the tradition of premium high-end microphone preamplifier design by using the very latest advances in FET and bipolar circuitry. Equivalent Input Noise (EIN) is the measure of a preamp’s noise floor, the lower the number the better. This new microphone preamp’s EIN of -126 dBV (A-weighted) is believed to be one of the quietest transmitter lavalier preamps available. It is on par with high-performance balanced XLR preamps. Additionally, the preamplifier can handle signals in excess of +5 dBV, which is the maximum level that any lavalier powered from 5 V bias can produce. Extensive listening tests were performed to ensure pristine sound quality which can meet the most demanding applications.

Multiple-ADC Architecture

Following the microphone preamplifier in the signal path, the microphone’s audio signal needs to be converted from analog audio to a digital bitstream using the analog-to-digital converter (ADC). The A20-Mini uses Sound Devices’ patented (US9654134B2) multi-ADC topology to capture the entire dynamic range of lavalier microphones plugged into its LEMO connector. The signal is captured with full fidelity, with little added noise, and no loss in headroom. Multiple ADCs are required since, as of this writing, there are no ADCs on the market with a dynamic range greater than 130 dB that run efficiently off of battery power.

Floating-Point RF Transmission

With GainForward, the signal’s entire dynamic range is preserved and sent digitally via RF over the air to the receiver using floating-point math. Somewhat similar to how 32-bit floating point audio files have increased dynamic range, a related “Floating-Point RF” method is used to send digital audio over the RF link. Audio samples are converted from fixed-point coming out of the ADCs into a floating point representation. At the receiver, the reverse process takes place and the floating point signal is converted back into fixed-point audio. This entire RF encoding and transmission topology is proprietary to Sound Devices. It has evolved over many years of work and listening tests, and is the very heart of every A20-Mini system.

FAQ:

Does this mean I don’t need to have low-sensitivity lavs anymore such as the Sanken COS-11 red dot? 

No, low-sensitivity microphones are still needed for very loud sounds. Lavalier microphones themselves inherently have a more limited dynamic range than larger diaphragm microphones. Even though the A20-Mini itself can handle the entire acoustical and electrical dynamic range of any lav microphone plugged into it, lavs themselves can saturate with high SPL sources. Therefore there is still a need for different sensitivity lavalier microphones.

Is the Bluetooth connection being used to remotely control the gain of the transmitter?

No, there is no remote control of the gain circuitry at all. There are two advantages to this over a system which does perform remote gain control of the transmitter: a) if the transmitter is out of range of Bluetooth/remote control, the gain can still be controlled by the mixer; b) the gain can be controlled as quickly as you can move the trim knob.

Can I use a non-Sound Devices mixer and get the benefits of GainForward?

Yes, the A20-Mini and A10-RX can be used with virtually any brand of mixer. Use the gain control, low-cut, and limiter built into the A10-RX’s menu to control these functions.

Can I come out of the A10-RX via the analog output and still get the benefits of the GainForward architecture? 

Yes, provided you use the gain control provided on the A10-RX itself.

Does the AES output of the A10-RX have enough dynamic range for GainForward?

Yes, AES can transport 144 dB of the audio’s dynamic range, so it is definitely sufficient for the >130 dB of dynamic range of the lav microphone.