Abstract: An FM or PM signal is demodulated so that the cycle time of the modulated input signal is measured using a time-to-digital converter comprising a counter that uses a moderate clock frequency as a reference clock, a digital delay line interpolator and a control circuitry. The counter is used for rough digitization and the delay line for interpolating the moment of zero-crossing inside a clock cycle. Total delay of the delay line, i.e., the range of time intervals the interpolator is able to measure, is actively kept equal to the cycle time of the reference clock. When the number of delay elements in the delay line is a power of two, the result of the delay line interpolator may be used directly as the least significant bits of the measurement.

Abstract: Device for listening to and recording of the sounds produced by birds or other distant objects. The device (FIG. 1) is attached to a pair of binoculars or a telescope and consists of one or more directional microphones, microphone structures or sets of microphones, a microphone and headphone amplifier and a pair of headphones, the directional microphone structures (2, 3) and the amplifier unit (4) with the headphones (7) being attached to the binoculars (1) by suitable means. An audio signal can be supplied from the amplifier to an external recording device, or a recording device may be integrated with the device of the invention. Used together with a pair of binoculars or a telescope, the device provides a light and easy-to-use means of audiovisual observation of distant objects, and when provided with an integral or external tape recorder it is also suited for amateur use for the recording of wildlife sounds.