# How to make pulse wave from sine wave - audio frequency

I'm looking for a quick-and-dirty way of converting something close to a sine wave to a narrow pulse wave. Please see the image: a low bass note played through a broken transformer. I'm trying to re-create the effect, preferably using discrete components.

• try 'Low pass filter + zero crossing comparator'. Nov 19, 2014 at 8:12
• Yeah I was thinking of some sort of a zero crossing detector. But I'm not good at designing circuits and I haven't really found a simple low voltage one (preferably with transistor(s)).
– Jari
Nov 19, 2014 at 8:31
• It is very important to perform lowpass filtering (integration) prior to zero-crossing detection.
– LvW
Nov 19, 2014 at 10:27
• OK thank you! I found this circuit, a good one to start with? sound.westhost.com/appnotes/an005-f1.gif
– Jari
Nov 19, 2014 at 12:06
• You show an output waveform and clearly there are pulses but what is the stuff in-between - is it noise that you don't want or part of the input signal? Are the pulses coincident with a certain part of the input waveform i.e. zero cross of input or possibly the peak voltage? Are there in fact many pulses per cycle? I cannot tell because I can't see the input waveform. Nov 19, 2014 at 13:14

## 1 Answer

There is a way to convert a cosine and sine waves into a pulse. I do this in RF.

First of all you have to have both real and imaginary waves. We start with just a real wave and then perform a complex multiply. After some digital filtering you get both real and imaginary waves. For my project there are about 2 or 3 cycles at some frequency.

From trigonometry, cosine^2 + sine^2 = 1;

Your perform this equation on each sample.

This will give you a pulse.