(aka, How To Tickle The Red)
One of the most misunderstood settings on a wireless audio transmitter is the audio input gain, and we’ll explain some basics on how to set yours to get the results that you need. It’s easier than you think!
Most Lectrosonics transmitters allow variable gain in 1dB steps over a range of 44dB. The SSM offers an additional 7dB of attenuation at the bottom end of the gain range, to use with high output lav mics or with loud singers (typical in musical theater situations). Our HM and HMa plug-ons give you an additional 10db of gain at the top end to use with low sensitivity dynamic mics. Why do we offer this level of fine control? To optimize the signal to noise ratio – but we’ll get to that in a minute.
Three factors that affect how you set your gain are:
- How loud is the sound source? Are you recording spoken word? Singing? Instruments? How much variance in volume is there? Highs and lows? Consistent?
- How far is the sound source from the mic? And, is the sound being transmitted through a lav? A handheld? A parabolic? You need to look at distance and the type of mic you’re using.
- How sensitive is the mic that you're using? To continue the above, are you using a condenser mic? Or even an old ribbon mic? Most lav mic manufacturers offer models with the same capsule but different sensitivity levels.
Optimizing Signal to Noise Ratio
Signal to noise is the ratio of desired signal to the noise in the system. Our Tech Note 1016 discusses this concept in detail. All wireless systems have noise - whether in the system (usually heard as a hiss) or riding along with the radio channel signal as mild interference (apparent as pops and crunches). You'll almost always hear the presence of channel noise if the mic is at the very edge of its range. To compensate for this, you'll want to turn up your audio gain on the transmitter enough so that you get a good signal to noise ratio (desired signal to noise floor). The way that you know you have a good ratio is by bumping up against the limiter in the transmitter so that the LED lights up - or what our techs call "tickling the red" on audio peaks. The limiter is a circuit that monitors the audio level and makes sure that it doesn’t distort or overmodulate the signal. On Lectro units, look for this by first checking your input levels, which show on the screen or via the bi-color LEDs. You would adjust the levels until you see the limiter indicator turn on briefly on peaks. The manual for your transmitter, as well as the card that ships with all units, will explain how to set it:
All units have a -10 and -20 LED. If you get a faint signal, the LEDs are green. Once you bump the limiter, you will see the -20 LED turn red.
The -20 LED is key to setting gain on Lectrosonics transmitters. Too low of a gain setting with any FM-based wireless system (including our Digital Hybrid Wireless® series) can affect your range in that your sound source can get lost in the noise floor. Too high of a gain setting will result in excessive limiting and possibly distortion, which is just as undesirable.
The loudest part of what you are recording should hit the peak while providing a good amount of headroom. Headroom is the difference between the loudest sound and 0dB (which is where sound clips or gets distorted). 30dB is a general starting point for the conversational speaking voice. Lectrosonics systems also have squelch based on pilot tones and SINAD (signal to noise and distortion) built in. If the SINAD is too low, the receiver will cut off the audio signal to prevent drop outs, thus shortening your range.
For those of you who use SMB or SMWB transmitters, customer Matt Price from SoundRolling.com put an excellent video on YouTube with basic gain setting suggestions.
One of our most popular videos covers this topic as well, and the bonus is a roadrunner cameo!
Our video with Phil Sousson reviews settings for the LMb and LT, particularly for bass and guitar, but useful for other applications as well
Our Wireless Side Chat #2 discusses gain structure in a few different scenarios.