# Re: [music-dsp] Finding discontinuity in a sine wave.

```This all works well in an ideal system. Suppose the sampling clock is drifting
slowly over period of time,
then the notch filter will fail to filter it. How to detect and correct these
clock drifts and have a stable notch filter.```
```
-ben

________________________________
From: music-dsp-boun...@music.columbia.edu
<music-dsp-boun...@music.columbia.edu> on behalf of Ethan Fenn
<et...@polyspectral.com>
Sent: Wednesday, January 10, 2018 10:33 PM
To: music-dsp@music.columbia.edu
Subject: Re: [music-dsp] Finding discontinuity in a sine wave.

If the sine frequency is f and the sample rate is sr:

Let C = cos(2*pi*f/sr)

For each sample compute:

y(t) = x(t) - 2*C*x(t-1) + x(t-2)

y(t) should be 0 for every t... if not it indicates a discontinuity. This is
just an FIR filter with a zero at the given frequency.

-Ethan

On Wed, Jan 10, 2018 at 11:58 AM, STEFFAN DIEDRICHSEN
<sdiedrich...@me.com<mailto:sdiedrich...@me.com>> wrote:
So, the notch filter will have an output, a PPL would need to re-sync, etc.

Steffan

On 10.01.2018|KW2, at 17:51, Benny Alexandar
<ben.a...@outlook.com<mailto:ben.a...@outlook.com>> wrote:

But if there is a phase discontinuity it will be hard to detect.

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