Hiss

Simple Explanation

The soft "sssss" sound you might hear from a speaker, an old cassette tape, or a radio when no music is playing. It is the natural background noise of electronic equipment.

Concise Technical Definition

A form of random, broadband high-frequency noise (typically between 2 kHz and 20 kHz). It represents the noise floor of an electronic system and is usually caused by the thermal movement of electrons within transistors, resistors, and other components.

Layman-Friendly Analogy

Think of hiss like the sound of a distant waterfall or a light breeze through trees. It’s a constant, steady background sound that is always there, but you only really notice it when the "main event"—like someone speaking or music playing—stops.

Industry Usage Summary

Common in analog tape recordings, preamps, and lower-quality digital systems; it is often masked or reduced using noise-reduction tools. In the high-end audio industry, "hiss" is a critical metric for amplifiers. High-sensitivity speakers (like horns) can make even a tiny amount of hiss audible, which is why professionals prioritize amplifiers with an extremely low noise floor to ensure a "black background" during quiet passages.

Engineering Shortcut

The Noise Floor. If hiss is too loud, check your Gain Staging: ensure you aren't boosting a weak, noisy signal with too much gain later in the chain. Improving the signal-to-noise ratio (SNR) at the source is the best way to "kill" hiss.

Full Technical Explanation

Hiss is a type of broadband noise, generally concentrated in the 2 kHz to 8 kHz range and above, often described as sibilant or static-like. In electronics, it is primarily a result of thermal noise (also known as Johnson-Nyquist noise). It occurs in all active and passive components as electrons fluctuate due to temperature. In analog media, such as magnetic tape, hiss is caused by the physical grain of the magnetic particles on the tape.

In digital systems, hiss may arise from quantization noise or suboptimal analog-to-digital conversion. While hiss is not as intrusive as low-frequency "hum" (60 Hz/50 Hz) or "buzz," it significantly degrades the dynamic range of a system. High-sensitivity speakers are more likely to reveal this noise floor, making it essential to use components with high SNR ratings. Noise reduction systems, such as Dolby NR, were specifically developed to compress and then expand the high-frequency signals to "sink" the hiss below the level of audibility.