There are many forms of electrical noise; but more generally speaking, electrical noise consists of electrical voltages or current flow induced by some outside interference, intrinsic “self-noise” of active electronics, static electricity, or some combination of these. Some of the most common forms of electrical noise are:
- 60 Hz. hum induced by electrical circuits within the building or structure.
- Static electricity typically caused by loose connections, bad wiring, or plugging and unplugging electronic instruments before muting the channel, for example: unplugging an electric guitar on an open channel.
- Self-noise, also known as intrinsic noise or Johnson noise, exists in all active electronic circuits, and is more common in low-cost consumer grade components and instruments. Active electronics are found in condenser microphones, keyboards, electronic drums, amplifiers of all types, and some direct boxes.
Three ways to eliminate or reduce electrical noise:
- Keep signal paths as short as possible, and form right angles where signal cables cross electrical lines.
- Use the best high-def, low-noise, or noise cancelling signal cables that you can afford.
- Get rid of as many active electronic components in your signal chain as practical.
Signal cables behave like antennas. The more you have in use, and the longer they are, the more noise will be picked up by your cabling and injected into your sound system. Do not use a 25 foot cable when a 6 foot cable is more appropriate. Stay away from disposable cables altogether. Those are the ones that usually cost less than $10 each and they have cheap no-name connectors on the ends. The signal wire in those cables is purchased in bulk from whichever manufacturer has the lowest bid for that manufacturing cycle; most commonly only second grade wire is used for this purpose. Furthermore, the wire may change from one manufacturing cycle to the next; so you never truly know what you are getting. The cables are disposable because no service or warranties are available for this type of cabling.
Absolutely the most effective way to eliminate electrical noise is to eliminate its source.
Most electrical noise is of the intrinsic type. It is the noise generated within active electronic circuitry; for example, turn on a guitar amplifier and you will hear intrinsic noise, but place an acoustic guitar on a stage and you will hear nothing. The guitar amp has active electronic circuitry in it which is a source of electrical noise. The acoustic guitar is a passive acoustical instrument and does not generate electrical noise. The same is true of digital pianos vs. acoustical pianos. A digital piano will add some electrical noise to your signal; however, a grand piano will not make a sound unless it is played. The grand piano cannot create electrical noise, because it has no active electronics in it—it is an acoustical instrument.
The signal to noise ratio is a very important consideration when choosing replacements for what use to be all acoustical instruments. The signal to noise ratio is the ratio of desirable signal to that of the undesirable noise. It is useful to quantify the amount to which noise has corrupted the original acoustical signature of the sound. You will find a signal to noise ratio on all active electronic devices. The capsule of a condenser microphone produces a very tiny signal which must be amplified by a factor of more than one-thousand by an active preamplifier circuit within the microphone. For this reason, all condenser microphones are prone to self-noise, and their makers must publish the signal to noise ratios of these microphones.
The Shure SM87 is a popular vocal condenser microphone with a S/N rating of 70dB. This means that the microphone produces 24dB of self-noise. We know this because microphone sensitivities are taken at 1 Pascal which equals 94dB, and 94dB minus 70dB of signal leaves 24dB of undesirable noise. In contrast, the ever popular Shure SM58, a dynamic vocal microphone, does not have a signal to noise rating because it is a passive microphone and contains no active electronics. As such, it does not introduce any noise of its own into the signal path. With that in mind, one should make careful selections of electronic instruments and equipment that will be present in the signal chain. Eliminate every piece of active electronics that you can rid your system of to thwart as much electrical noise as possible.