Tuesday, November 4, 2008

Waveform analysis of Tongue Clicks for use with Echolocation

For this post, I have analyzed three of the more popular methods of clicking. Using a studio recording microphone (AKG Perception 200) I recorded myself clicking to the best of my ability. The three clicks in question here are:

The "Cluck": Made by lightly pressing the tip of the tongue against the roof of the mouth and then breaking the vacuum and smacking your tongue against the floor of your mouth.

The "Giddyup": This one is made by breaking the vacuum and drawing air in between the sides of the tongue and the molars, and is commonly used to communicate with horses. This signal, by nature, is produced at the sides of the mouth, and therefore is emitted away from the sides of the head. This is interesting in that we can send the signal to either one side or the other, but it is more difficult to send the signal directly to the front with this method.

The "Blade Pop": This one is the most difficult for me, but sounds like the one used by many proficient echolocators. This requires that you suck the blade of your tongue (the big meaty part in the middle) up against the roof of your mouth until you've got a good amount of surface-to-surface contact, and then break the vacuum by pulling your tongue away. This one requires significantly more vacuum than the previous two. When executed correctly, it sounds distinctly like a bottle cap being depressed or released.

The frequency of all three clicks described above can be adjusted slightly by the shape of the mouth. Generally a wide mouth or smile will generate a higher primary frequency, as well as make you appear happy :)

Signal Analysis

Below, I've uploaded the waveform generated by each of these clicks, as well as a spectrum analysis. The waveform shows the amplitude of the sound over a certain time period (as indicated), and the spectrum analysis is a plot that lines up with the waveform and shows the distribution of frequencies that occur within the sound signal. Brighter colors meaning higher concentration of waves in that region. Higher frequencies are at the top and lower frequencies at the bottom of the spectrum analysis.

The Cluck (200ms):

The cluck waveform is neat because you can distinctly see two spikes. The first small spike is the tip of the tongue separating from the roof of the mouth, and the second spike is the tongue smacking against the bottom of the mouth. Although the latter is significantly more prominent than the former these two sounds are within 10-15 ms of one another and have the potential to cause interference to the listener. This signal could introduce ambiguity.

The spectrum analysis shows that most frequencies coming from the cluck signal are quite low. The higher the frequency, the more energy it has and it also allows for better recognition and better resolution. (See Properties of a Good Echolocation Click) A broad distribution of frequencies would theoretically give you a reliable signal since some frequencies will be absorbed by objects and others will be reflected depending on the resonant frequency of the material or object.

The spec to the right of the actual signal is not an echo, but actually a drop of saliva swishing around in my mouth as an artifact of the signal creation.

This is the signal I started with, but have not had a lot of luck using it effectively. I think this is primarily because of the concentrated low frequency and "double pop".

The Blade Pop (100ms):

Notice the sound envelope as compared to the "Giddyup" below. The "attack" (time it take for the signal to get from zero to peak amplitude) is much less for this signal. Approx. 7ms for the Giddyup, as opposed to about 1ms for the Blade Pop. This gives the signal more of a distinct "pop" which will actually impact objects better and thus be reflected better. Think of it has a "harder" signal. A superball bounces better than a sponge. In other words, the object can be absorbative making it difficult to bounce a signal off of, but the signal can also be "squishy", making it easier for the object to dampen the impact as opposed to reflecting it.

Notice that there is fairly good distribution of the signal although there is a blank spot, and there could be more in the high end which would make for a better signal. If you look at the spot about 70% through the spectrogram, you'll see a faint echo of the higher frequencies. This is approximately 70ms from the generated signal and probably corresponds to the shape of the signal bounce pattern in the room. A 70ms delay would mean approximately 70 feet of signal travel, so this signal is more like an echo after the signal has bounced around the room a while as opposed to the instant ricochet off of the nearest wall.

This being the sound that I am struggling with, it may be that, with practice, I could distribute the signal over a wider range of frequencies and become more accustomed to its sound.

The Giddyup (300ms):

The signal itself has a 7ms attack as discussed above, and the signal itself is about 25ms as opposed to 12ms for the Blade Pop.

Good distribution of the signal, a little ricochet at about 70ms on the higher frequencies. As mentioned above, this one is directed away from the sides of the face, which may or may not be a good thing. It's nice that it is more inline with the ears, but then you have to turn your head slightly in order to notice objects directly in front of you.

This is the signal that currently gives me the most accuracy. I am accurate within 1/2 inch or so of flat walls whereas the Blade Pop only gives me accuracy down to 6 inches or a foot. I will need to play with that signal a bit more and report back, because I do like the distiction of it. It is much more "poppy" than the Giddyup.

I will need a more sound proof room and more controlled environment in order to directly observe the reflexive properties of certain objects with these clicks. It's a good thing the human brain is faster, smarter and more acute than any computer, otherwise we'd still need our eyeballs to see things.

Free 10-Minute Audio Lesson: Learn the Echolocation Click

Learn echolocation clicks with a free audio lesson
Learning how to click is one of the first steps to becoming an effective echoloator. This lesson provides clicking samples of a variety of different clicks and descriptions of when they might be most useful. This lesson has been used by O&M instructors all over the world.

Despite popular belief, it's easy to make your clicking quite subtle or unnoticeable even in quiet settings. There are many different clicks for different situations. I explain all of these in great detail and give examples of where, why and when they can and should be used.

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