How to find dominant frequency?

Yes I know I plot spectrum, everybody just says this. I want to know how to read plot spectrum to find the dominant frequency.

I am working on a school project to find how volume of water within a wine glass affects the frequency it plays at. I am using the most current audacity and I have a mic set up.

Usually it’s the tallest peak in the spectrum plot.

Find the highest blob and look straight down. Frequencies are along the bottom and volume along the left. You can help a bit by making the display larger left to right. Click on the window edges and pull. The numbers get more detailed the wider the display.

The Size value affects how detailed the display gets. I usually use the higher numbers. Lower numbers tend to smooch over the display and make it harder to read individual tones. Too high and you may get too much detail. Like trying to measure the hairs on your head or blades of grass on your lawn. In those cases fuzzy averages are good.

Log/Lin is selected depending on where you need the most accuracy. Log gives you 440Hz in the middle of the graph. 440Hz is the oboe tone at the beginning of the orchestra and “sounds” like it’s in the middle. Lin gives you 10,000Hz in the middle and while that’s technically true, it jams everything most people can hear in the left-hand quarter-inch of the graph.

That and many older people can’t even hear 10,000 Hz any more.

You may find that changing the pitch of the glass isn’t open ended. You can’t get any tone you want with wine level. As the glass fills up, it stops being a good resonant cavity and the quality of the tone gets ratty. Dampening Factor changes and Q goes down.

The quality of the tone from an almost full glass and the quality of tone from a tiny wine glass are really different, even if they’re the same frequency or pitch. You may be able to see that in the spectrum display. It will be harder and harder to pick out the high blob.


Pick a wine glass with straight sides if you can. Those are easier to calculate resonance with a ruler even though they don’t sound as cool.


Dampening Factor changes and Q goes down.

I wonder if you could avoid that problem by not using wine or water. Fill it with mercury (don’t try this at home) or cement or concrete. Something easier to get like plaster or grout. Water can have its own resonance (ripples in a pond). Plaster doesn’t. Plaster just sits there.


Oh, one more. Drag-select the sound after the impact. Smacking the wineglass is an unrestricted impulse and contains many frequencies. It will mess up the actual ring or tone measurement.


I know how to mop the floor with your competition. Get 13 wine glasses and create one musical octave with water level. Google the frequencies. Then play a tune with a spoon.