Signal to noise (s/n) ratio is the level of signal power in relation to the power of noise surrounding that signal, measured in decibels (dB). With wireless systems, the quality of your sound is largely dependent on achieving the highest signal to lowest noise ratio possible. So how can we do this? First, we need to look at the cause and type of noise in question. "Noise" is any type of competing signal interference – unwanted tones, static, even other frequencies - within the physical space. If you’re using wireless microphones, your noise may also be a result of channel noise in the FM process. “FM,” because all analog wireless systems use frequency modulation to send audio signals. A component of the FM process is the Capture Effect: wireless receivers will always demodulate (turn into audio) the strongest RF signals within a given frequency, and that includes sounds that you don’t want.
In order to combat the noise, you’ll need to look at the physical space you’re operating in, which is your working environment and also any equipment in your environment. Four tips to consider:
1) Check the distance between the transmitter and receiver
In general, the closer transmitters and receivers are to each other, the better your signal. This is the Inverse Square Law at work. It states that the intensity of a radiated signal is inversely proportional to the square of the distance of the wave from the signal source. If you double your distance, the signal strength is reduced by a factor of four (and the reverse is true, too). When possible, use the least practical amount of unobstructed distance between transmitter and receiver.
Are you getting interference from outside your venue or area? Walled structures, in combination with wireless mics, are effective shields against what might intrude from the outside, as RF does not easily travel through dense solids. Wireless mics are not without their issues – attenuation being one. We cover attenuation in Wired List #8. In extreme cases where you are indoors and still getting interference, and if you can’t change frequencies, look for sources of interfering RF and either shield them or increase the distance from them to your receivers (see #1).
Directional antennas, when used correctly, can be used to improve s/n ratios. They should be affixed above head height (10 ft is a good rule of thumb), with a clear line of sight to the receiver. By orienting them so that their null sides are “pointing” at unwanted sources of RF (local TV towards, etc.) the RF s/n ratio is further improved. We published a list of common antenna combinations for our equipment in Wired List #12. If you're using coax cables to bridge distance, inspect them before use, as wear and defects can cause a loss of signal. All coax cables result in losses of signal strength, depending on the cable material and length. Some systems may benefit from in-line filters such as our PF 25 or PF 50 or filter/amplifiers, such as our UFM144. In reference to this topic and to #3 above, a powerful tool for many systems is the ALP690 active/passive antenna with selectable amplification, attenuation, and filtering.
4) Increasing Transmitter Power
If nothing else works, you can try increasing your transmitter power. Be advised that this can often result in increased noise in the general RF spectrum, which might be counterproductive. Additionally, licenses are required in some localities to operate transmitters over certain thresholds. You can check to see who the licensing body in your locality is here. Our recent Wireless Side Chat series on YouTube are good primers to review if you’re looking to improve your signal quality, because we often don’t consider the technical considerations behind cause and effect. If you missed them, they are:
#1: Introduction to RF Spectrum for Wireless Microphone Use
#2: The 7 Most Common Wireless Mic Problems and How To Solve Them
#3: Wireless Designer Software New Features, Tips & Tricks