Transient noise filter employing crosscorrelation to detect noise and autocorrelation to replace the noisey segment

A method for substantially eliminating transient noise pulses in an input signal, comprising the steps of:

• receiving the input signal containing transient noise pulses;
• receiving an alternate input signal containing transient noise pulses whose occurrence times are substantially the same as the occurrence times of the transient noise pulses in the input signal;
• producing a first signal through filtering of the alternate input signal within selected frequency limits;
• producing a second signal by detecting the absolute amplitude envelope of the first signal;
• developing an envelope signal from said second signal and convolving said envelope signal with a predetermined filter function to generate a convolution signal;
• detecting pulses in the convolution signal which have predetermined pulse amplitude and duration characteristics;
• producing a detection signal when one of said pulses is detected;
• receiving the input signal and producing a third signal delayed relative to the input signal by a preselected duration;
• receiving the input signal and producing a fourth signal which is a time weighted estimate of the third signal in time versus amplitude;
• and
• switching between the third signal and fourth signal as controlled in response to production of said detection signal to produce an output signal.

A circuit for substantially eliminating transient noise pulses in an input signal, comprised of:

• frequency filtering means receiving the input signal and producing a first signal containing those frequencies of the input signal likely to contain significant components of the transient noise pulses;
• absolute value determining means receiving the first signal and producing a second signal related to the absolute value function of the first signal;
• envelope determining means receiving the second signal and producing a third signal related to a function of the envelope of the positive portion of the second signal;
• pulse shape discriminating means receiving the third signal and producing a fourth signal related to the convolution of the third signal with a predetermined filter function;
• threshold trigger means receiving the fourth signal and producing a detection signal when the level of the fourth signal exceeds a predetermined threshold level;
• time delay means receiving the input signal and producing a delayed input signal related to the input signal by a predetermined time delay;
• and,
• output means receiving the input signal, the delayed input signal and the detection signal, having a gating portion for producing an output signal varying between the delayed input signal and an estimate signal, as a function of the level of the detection signal, and a signal estimating portion for producing the estimate signal as a function of the input signal and the output signal, the estimate signal being an estimate of the delayed input signal.