Hearing aid with an oscillation detector, and method for detecting feedback in a hearing aid

A hearing aid comprising:

• a microphone which receives an input acoustic signal and converts said input acoustic signal into an analog input signal;
• an earphone which emits an acoustic output signal;
• a signal path between said microphone and said earphone containing signal processing circuitry for processing said analog input signal;
• and
• an oscillation detector for detecting oscillations in said signal path as an indication of acoustic feedback in said signal path, said oscillation detector comprising an analog-to-digital converter supplied with said analog input signal for producing digitized sample values in consecutive periods of said analog input signal, a period measuring element supplied with said sample values for determining respective numbers of said sample values in said consecutive periods, a first averaging element for determining a long term average NL of said respective number of sample values, a second averaging element for determining a short-term average NK of said respective numbers, of sample values, a difference element for forming a difference between NL and NK, an absolute value element for forming an absolute value of said difference, a third averaging element for smoothing said absolute value of said difference to obtain a smoothed difference value, and an analyzer element supplied with said smoothed difference value and detecting oscillations in said signal path when said smoothed difference value is substantially zero.