Earphones for measuring and entraining respiration

A method of adjusting sounds heard by a user of an earphone, the method comprising:

• providing output audio signals to a loudspeaker supported by a housing and acoustically coupled to the user's ear canal by an ear tip surrounding the housing and acoustically closing the entrance to the user's ear canal;
• receiving input audio signals from a microphone in the housing and also acoustically coupled to the user's ear canal by the ear tip;
• and
• in a processor
• extracting a rate of respiration from the input audio signals;
• adjusting the output audio signals based on the extracted rate of respiration;
• and
• providing the adjusted output audio signals to the loudspeaker,
• wherein:
• the step of providing the output audio signals to the loudspeaker comprises providing signals which represent sounds across a first frequency band, the audio signals including a notch in which the sounds lack energy within a second frequency band narrower than the first frequency band;
• and
• the processor is configured to extract the rate of respiration by
• applying a band-pass filter to the input audio signals to limit the input audio signals to a third frequency band contained within the second frequency band;
• and
• demodulating the filtered input audio signals to compute the rate of respiration corresponding to energy in the input audio signals in the third frequency band.