Gain compression is a reduction in differential or slope gain caused by nonlinearity of the transfer function of the amplifying device. This nonlinearity may be caused by heat due to power dissipation or by overdriving the active device beyond its linear region. It is a large-signal phenomenon of circuits. Relevance Gain compression is relevant in any system with a wide dynamic range, such as audio or RF. It is more common in tube circuits than transistor circuits, due to topology differences, possibly causing the differences in audio performance called "valve sound". The front-end RF amps of radio receivers are particularly susceptible to this phenomenon when overloaded by a strong unwanted signal. Audio effects A tube radio or tube amplifier will increase in volume to a point, and then as the input signal extends beyond the linear range of the device, the effective gain is reduced, altering the shape of the waveform. The effect is also present in transistor circuits. The extent of the effect depends on the topology of the amplifier. Differences between clipping and compression Clipping, as a form of signal compression, differs from the operation of the typical studio audio level compressor, in which gain compression is not instantaneous (delayed in time via attack and release settings). Clipping destroys any audio information which is over a certain threshold. Compression and limiting, change the shape of the entire waveform, not just the shape of the waveform above the threshold. This is why it is possible to limit and compress with very high ratios without causing distortion. Limiting or clipping Gain is a linear operation. Gain compression is not linear and, as such, its effect is one of distortion, due to the nonlinearity of the transfer characteristic which also causes a loss of 'slope' or 'differential' gain. So the output is less than expected using the small signal gain of the amplifier. In clipping, the signal is abruptly limited to a certain amplitude and is thereby distorted in keeping under that level. This creates extra harmonics that are not present in the original signal. Soft clipping or limiting means there isn't a sharp knee point in the transfer characteristic. A sine wave that has been softly clipped will become more like a square wave, with more rounded edges, but will still have many extra harmonics. Compression Compression of gain is caused by non-linear characteristics of the device when run at