Last month we took a look at various types of noise. Whether you realize it or not, noise has a big impact on the way recordings are made.
One of the specifications you will frequently see on audio equipment is signal-to-noise ratio, abbreviated as SNR or S/N. It is the ratio of the level of the nominal audio signal to the level of the background noise (noise floor), usually expressed in decibels (dB).
Another term whose definition sounds very similar to SNR is dynamic range. Dynamic range is the ratio of the maximum operating level to the level of the background noise. The only difference between the definition of these terms is the starting point. For SNR, it's the nominal operating level, while dynamic range measures from the maximum operating level.
The nominal operating level (also called nominal audio level or simply nominal level) is the normal signal level at which a piece of audio equipment is designed to operate. The maximum operating level (also called the maximum output level, both abbreviated at MOL) is the level for a device at its maximum usable audio level. For analog signals, maximum output level is often defined as the highest output that does not exceed 3% total harmonic distortion (THD). For digital signals, it is defined as 0 dBFS. There is even a more precise definition for magnetic tape, but we will not get into that here.
The difference between nominal operating level and maximum operating level is headroom. Headroom provides a buffer zone to allow for unexpected transients without risking clipping or causing excessive distortion.
So how do these terms affect the way recordings are made? Well, in the old days when everything was recorded on magnetic tape, a good engineer would try to record at the highest level possible. A recording with too low of a signal would allow the noise (primarily hiss) to become too prominent, especially in quieter passages. If the signal was too high, distortion could become a problem. It was not always easy to hit the right level. You can still find recommendations that all recordings should be recorded as “hot” as possible, but that really does not apply to digital recordings.
Most digital recording today are recorded at 24 bits or higher. The reason for that is the fact that the dynamic range of a digital signal is a function of its bit depth. (See table.) A 24-bit signal has more than 48 dB greater dynamic range than a 16-bit signal, the bit depth of a standard compact disc. So if you allow for a headroom of 20 dB, you still have a dynamic range 38 dB higher than that of a CD. That fact makes setting recording levels on digital recording much more forgiving than on analog recordings. The noise floor on a digital recording is many thousands of times lower than that of an analog recording, and that is no exaggeration.
• The backup band for the 1963 hit “He's So Fine” by the Chiffons was the Tokens, who had a No. 1 hit in 1961 with “The Lion Sleeps Tonight.”
• The backup band for the artists touring with Dick Clark's Caravan of Stars in 1965 were members of the band Exile. The show included artists, such as Del Shannon, the Ad Libs, the Shangri-Las, Brian Hyland, and Tommy Roe. In 1978, Exile would score a No. 1 hit with “ Kiss You All Over.”
• The girl group the Shirelles consisted of Shirley Owens, Doris Coley, Addie (Micki) Harris, and Beverly Lee. However, when the single “Baby, It's You” was released, it had only Owens' vocal. The other members of the group were not on the record, as the original backup vocals used on the demo, provided by male singers, were left in place.
• The first time that Del Shannon performed “Runaway” on stage, his keyboard player Max Crook improvised the organ solo. From then on Crook used the same solo note for note for the recording and in all future performances.