A system, comprising: audio output transducers configured to transduce electrical output signals into acoustic sounds; a plurality of audio input transducers configured to transduce acoustic sounds into electrical input signals; and a signal processing device in data communication with the audio input transducers to receive as input electrical input signals, and in data communication with the audio output transducers to provide the electrical output signals to the audio output transducers, and wherein the signal processing device is arranged to execute instructions that cause the signal processing device to perform operations comprising: detecting, based on the electrical input signals and data describing a current auditory environment, a new sound that was not present in the current auditory environment before the detection, wherein the data describing the current auditory environment comprises data generated from electrical input signals received from the audio input transducers prior to the received electrical input signals from which the new sound was detected; adjusting the electrical input signals that are determined to be characteristic of the new sound to generate adjusted electrical signals in dependence on a classification of the new sound, wherein adjusting the electrical input signals comprises adjusting the new sound relative to the current auditory environment; generating the electrical output signals from the adjusted electrical signals that are determined to be characteristic of the new sound and from the electrical input signals that are not determined to be characteristic of the new sound; and providing, to the audio output transducers, the electrical output signals; characterized in that: generating the adjusted electrical input signals that are determined to be characteristic of the new sound comprises adjusting the electrical input signals that are determined to be characteristic of the new sound to cause a frequency shift in the new sound to distinguish the new sound in frequency relative to the current auditory environment when the adjusted electrical signals are used to cause the audio output transducers to generate audio output. audio output transducers configured to transduce electrical output signals into acoustic sounds; a plurality of audio input transducers configured to transduce acoustic sounds into electrical input signals; and a signal processing device in data communication with the audio input transducers to receive as input electrical input signals, and in data communication with the audio output transducers to provide the electrical output signals to the audio output transducers, and wherein the signal processing device is arranged to execute instructions that cause the signal processing device to perform operations comprising: detecting, based on the electrical input signals and data describing a current auditory environment, a new sound that was not present in the current auditory environment before the detection, wherein the data describing the current auditory environment comprises data generated from electrical input signals received from the audio input transducers prior to the received electrical input signals from which the new sound was detected; adjusting the electrical input signals that are determined to be characteristic of the new sound to generate adjusted electrical signals in dependence on a classification of the new sound, wherein adjusting the electrical input signals comprises adjusting the new sound relative to the current auditory environment; generating the electrical output signals from the adjusted electrical signals that are determined to be characteristic of the new sound and from the electrical input signals that are not determined to be characteristic of the new sound; and providing, to the audio output transducers, the electrical output signals; detecting, based on the electrical input signals and data describing a current auditory environment, a new sound that was not present in the current auditory environment before the detection, wherein the data describing the current auditory environment comprises data generated from electrical input signals received from the audio input transducers prior to the received electrical input signals from which the new sound was detected; adjusting the electrical input signals that are determined to be characteristic of the new sound to generate adjusted electrical signals in dependence on a classification of the new sound, wherein adjusting the electrical input signals comprises adjusting the new sound relative to the current auditory environment; generating the electrical output signals from the adjusted electrical signals that are determined to be characteristic of the new sound and from the electrical input signals that are not determined to be characteristic of the new sound; and providing, to the audio output transducers, the electrical output signals; characterized in that: generating the adjusted electrical input signals that are determined to be characteristic of the new sound comprises adjusting the electrical input signals that are determined to be characteristic of the new sound to cause a frequency shift in the new sound to distinguish the new sound in frequency relative to the current auditory environment when the adjusted electrical signals are used to cause the audio output transducers to generate audio output.