Fundamental frequency detection using peak detectors with frequency-controlled decay time

A method to detect a fundamental frequency of an input signal, the method comprising the steps of:

• providing dual peak detectors connected to an input signal to periodically sample a voltage of positive and negative peaks of the input signal, and then
• determining a fundamental frequency of the input signal from an output of the dual peak detectors, a decay time of each of the peak detectors being proportional to a time period between a pair of voltage peaks detected in the input signal, where an SR latch ensures that a peak of an opposite polarity has been detected between the pair of voltage peaks,
• wherein the dual peak detectors comprise switched-capacitor peak detectors, and
• wherein each peak detector comprises at least one capacitor, six switches for each capacitor, two op amps, and another switched capacitor network containing a different capacitor and four switches, a comparator, and a digital phase generator circuit.

A method to detect a fundamental frequency of an input signal having at least first and second harmonic components, the method comprising the steps of:

• providing dual peak detectors connected to the input signal to periodically sample a voltage of positive and negative peaks of the input signal, and then
• determining a fundamental frequency of the input signal from the output of the peak detectors, a decay time of each of the peak detectors being proportional to a time period between a pair of voltage peaks detected in the input signal, where an SR latch ensures that a peak of the opposite polarity has been detected between the pair of voltage peaks,
• wherein the time period between the pair of voltage peaks is used to adjust a decay time constant that determines a decay time for each peak detector,
• wherein the decay time is set to be long enough to avoid locking to the second or a higher harmonic depending on an instrument producing the input signal, but no longer than necessary to prevent cycle skipping when an audio signal decays, and
• wherein the decay time is adjusted so that bowed string instruments can have strong harmonic components at integer multiples of the fundamental frequency of the input signal and therefore require a longer peak detector decay time to avoid locking to these strong harmonics and audio sources with lower harmonic content can make use of shorter peak detector decay times without suffering tracking errors.