[cnvogel]

Noise-Cancelling headphones with external inputs, by their principle of operation, already have to funnel everything through a DSP. So it would be easy to implement a compressor/limiter for the external input signal. Is this feature available on any of the commercially available headphones?

As an explanation: A compressor/limiter is a device in audio processing used for leveling (compressing) the dynamic range, by making quiet things louder, and making louder things quieter. In the extreme case, one can configure a threshold of (power, loudness, amplitude, depending on the operation of the devices) which cannot be exceeded. [All you sound engineers, please excuse the simplification...]

https://en.wikipedia.org/wiki/Dynamic_range_compression