A broad definition of noise is any unwanted sound. If there are a bunch kids playing in the next room, the sounds they are making may be music to their ears, but if you are trying to watch television or read a book, it sounds like noise to you.
In a similar manner, any undesired sound in an audio system is considered noise. All audio equipment, no matter how expensive or well-designed has some noise. Inherent noise is the residual noise produced by an audio device itself. Such noise is caused internally by thermal vibrations (thermal noise), random disturbances, and other variations. Noise from external sources comes from electrical signals and radio frequency interence.
Audio equipment can be designed to minimize inherent noise through shielding and other means, but it cannot be eliminated completely. Even a microphone placed in absolute silence (if you could find such a place) will be putting out a very small amount of noise. All the noise contributed by each device in your audio chain, the microphone, the preamp, the amplifier, and other equipment contribute to the noise floor, the noise that occurs with no audio signal present.
Background noise has several meanings. It can refer to the inherent noise we just discussed. It also can mean the the ambient sound that is present at a location, such as wind, water, crowds, and traffic. This type of noise goes by a variety of names, such as ambient audio, ambient noise, ambience, atmosphere, atmos, or environmental sounds. Background noise also refers to the noise inherent in an audio storage medium, such as magnetic tape or vinyl records. Surface noise is produced by the friction of the stylus (needle) of a record player moving through the groove of a record. Magnetic recording tape is well known for contributing a constant level of hiss to the audio signal.
Hum is the undesired tone that occurs in an audio signal caused by interference from the ac power supply. Sometimes called buzz, it usually has a frequency or harmonic of 60 Hz (50 Hz in countries with 50-cycle power). Hum is the reason so much care is taken with shielding cables and equipment.
Did you know that noise comes in a variety of colors? You have probably heard of white noise, and maybe even pink noise. Noise color indicates the amount of energy that a sound has at various frequencies. It is somewhat analogous to the colors of light. White noise has the same energy content at every frequency. With pink noise, the energy level decreases at 3 dB per octave, so that each octave sounds equal in level to the human ear. On the other hand, black noise has no energy at all, that is, silence. There is also grey, red, blue, purple, orange, green, and brown noise. If you are interested, you may look up these terms in the glossary.
Next month we will look at several terms that depends on our understanding of noise.
• When RCA asked Kay Starr to record a song called “Rock and Roll Waltz,” she thought they were joking. At the time, rock and roll was still in its infancy and was frowned upon by serious musicians. After many arguments, Starr finally recorded the song, which went on to hit No. 1 in the US in February 1956 and remained on the charts for six weeks.
• Malcolm Young and Angus Young named their band AC/DC after the abbreviation for the electrical term for “alternating current/direct current.” They were unaware at the time that the term was also slang for bisexual. However, it helped get the band going because early in their career the band was hired to play many gay-themed events.
• Well-known New York deejay Murray the K was talking on the phone with his mother, when he mentioned that he and Bobby Darin were soaking their feet after playing a game of softball. It gave his mother, Jean Kaufman, a vaudeville piano player, an idea for a song: “Splish, Splash, take a bath...” Murray and Darin began writing the lyrics while Murray's mother composed the melody. “Splish Splash” became Darin's first Top 40 hit, reaching No. 3 in 1958.
• In 1964, Johnny Rivers hired Sylvester Stewart to play bass when he opened at the legendary Whisky A Go Go. When Stewart did not work out, Rivers promptly fired him. Two years later, Stewart reappeared as the leader of his own band, Sly and the Family Stone.