Dernière mise à jour : 2 août
Tone generators, also called frequency generators or synthesizers, can be used to conduct many exciting scientific experiments to understand sound waves.
In this article we describe 6 science projects that use the tone generator and which can be adapted to your specific needs.
Table of content
What is a tone generator ? - Create an acoustic beat - Generate an anti-sound - Synthesize the timbre of a oboe - Perform an audiogram - Protect yourself from too loud sounds - Measure the speed of sound
What is a tone generator ?
A tone generator, also called frequency generator, is an electronic device or software that produces audio tones at various frequencies and amplitudes. It is used for a variety of purposes, such as in music production, sound engineering, scientific research, and testing and calibration of audio equipment.
Tone generators can produce sine waves, square waves, triangle waves, sawtooth waves, and other waveforms. The frequency and amplitude of the generated tones can be adjusted to suit the specific requirements of the application. Some tone generators offer the ability to mix several tracks to create complex sounds.
In the old days frequency generators were bulky machines used in laboratories, but with the arrival of computers and then mobile phones, sound generators are now available in any digital equipment. They can be now used in the field, in class and importantly, they are free!
What are the best tone generators ? Well it really depends on what you intend to do with it and where you are. There are three types of tone generators :
on line generators (type in Google "Tone generator online") - the advantage is that it is easily accessible from any device but it needs internet access,
scientific apps (FizziQ, Frequency and Sweep generator, Audizr, Phyphox) - do not necessitate internet access, free and can be coupled with measurements,
synthesizers (Ableton, Studio one) - very powerful but needs musician expertise and are usually costly software.
In the following sections we will suggest a number of experiments can can be done using a tone generator to better understand sound and sound waves. We have used the free app FizziQ to conduct these experiments.
Create an acoustic beat
A sound effect often used in electronic music is the LFO effect, also called sound beat. In this effect the loudness of a sound increases and decreases periodically, like a siren. This effect can be reproduced very simply with the synthesizer.
Sound beat are interesting for pedagogy as the mathematical formula that describes the phenomenon can easily be derived from the analytical formula of the two sound waves. See this article to know more about the formula of acoustic beat.
To do an acoustic beat with FizziQ, open the synthesizer in the Tools tab of the FizziQ application. Add a second lane. set the first channel to 600 Hertz and the second channel to 602 Hertz. We then clearly hear the pulsation resulting from the periodic interference of the two sounds.
To experiment with acoustic beats, change the second frequency to 605 Hertz, the beat becomes very fast. Increase the deviation to 620 Hertz and the beat becomes inaudible.
To learn more about the LFO effect and physics, you can download the "Flume" activity on Acoustic Beats.
Generate an "anti-sound"
We talk a lot about anti-matter... so why not generate an anti-sound? This is the principle on which headphones that suppress background noise work. In this experiment we show how to cancel a sound.
Here is an experiment you can do with FizziQ :
Open the Synthesizer in the Tools tab of the FizziQ application.
Add a second lane. Set the first channel to 600 Hertz and the second to 600 Hertz as well, and both volumes to 50%.
Now playing this sound, we hear a pure sound.
Use the phase shift button to shift the second channel relative to the first. We note that the more we shift this button towards the middle, the more the sound is attenuated.
When the button is in the middle, that is to say when the second channel is half a period out of phase with the first, the sound disappears completely.
How does this work ? When the second channel is shifted by half a period compared to the first, the sound wave of the second channel is the exact opposite of the first channel and when the two sounds are played at the same time, they cancel each other out.
The same principle is used in noise canceling headphones: repetitive ambient sounds are recorded and analyzed, then they are replayed with a phase shift which allows them to be suppressed for the user.
To learn more about the cancellation of sound waves, you can download the activity "A bubble without noises" on the technology of headphones with active noise cancellation.
Synthesize an oboe sound
We often talk about the timbre of an instrument, but what do we mean by that?
Pure sounds are a single frequency sound wave. They are usually harmonious to the ear but a bit dull.
If we add to it another pure sound whose frequency is a multiple, we then have a sound that seems richer, more pleasant to the ear. This is an harmonic sound, ie a sound made of frequencies that are integer multiple of the fundamental frequency.
If we add two sounds that are not harmonics, they can still sound harmonious if their frequencies are specific ratios, like 3/2 (fifth), 4/3 (fourth), 5/4 (third) or 5/3 (sixth). This is the base of the music scale devised first by Pythagorus and adapted in the following centuries.
If we add two pure sound randomly, chances are that they will sound awful together. There are some exception though, like the sound of bells which are not harmonic sounds but still are pleasing to the ear.
Why do humans like better harmonic sounds ? This is still a mystery but one explanation is that nature usually produces non harmonic sounds. As human beings are social animals, it is an advantage if their brain can filter better specific signals and speech from other human beings, and so our brain would have evolved in this direction.
Timbre is the particular sound that an instrument makes and which is due to all the frequencies that are added to the frequency of the note played, the fundamental frequency.
Let's experiment with the production of complex sound and timbre. We will try to recreate the sound of a flute :
In the sound library, we choose the sound of the flute and we listen to the sound. The note played has a frequency of 880 hertz.
Now take the synthesizer and play a pure sound of this frequency. By comparing the two sounds, that of the flute and that of the synthesizer, we hear that these sounds do not sound the same.
We will now add other voices to the synthesizer and try to recreate the exact sound of the flute.
Add two voices to the synthesizer sound, 880 hertz and 1760 hertz, and try to adjust the levels to create the same flute sound.
Add another third voice at 2600 hertz and again adjust sound volumes
Now try with another sound, like the Oboe in the sound library. Can you achieve the same result ?
This simple experiment raises very interesting questions about the pitch of a musical instrument : How many frequencies does it include ? Is the sound very sensitive to the selected volumes? Can we verify the result by analyzing the frequency spectrum of the sound of the flute?
From the age of 60, the sensitivity of our hearing decreases greatly in high-pitched sounds. One experiment involves asking a 60-year-old person to perform an audiogram with a cell phone. Be careful, never put a loudspeaker close to someone's ear or subject someone to too high a volume, as this could cause irreversible damage.
To test hearing, we will create sound beats at various frequencies and then note the volume at which this person heard the sound. We use beats because it allows us to discern the sound with the phenomenon of pulsation. The laptop is placed on a table about 1 m from the person. First let's create a beat at 1000 hertz by creating two channels on the synthesizer, one at 1000 hertz and the other at 1001 hertz. We put the volume to the minimum then we gradually increase the volume of the smartphone until the person hears the sound. The volume level is noted in a table in the experiment book and then the operation is carried out for 2000, 4000, 6000 and 8000 hertz. By entering the data in a table, the audiogram is created.
Now compare this audiogram to your own audiogram. Please note, in order to be able to compare these two audiograms, they must be made under the same conditions with the smartphone placed at the same distance from the subject.
Measure sound attenuation as a function of distance
Emma is at a concert and is 2 meters from a speaker. It measures the sound level which is 105 db. With this power, she cannot stay in this place without risking damage to her hearing. At what distance should she be placed from the speaker so that the sound is 90 db and she can follow the whole concert without risk?
We can easily experience the scaled-down experience with our smartphone. We will need two smartphones with FizziQ installed and a ruler. One of the smartphones will be used to measure the sound level, the other to emit stable sound with the synthesizer. First we will locate on the device that measures where the microphone is. On the receiving device, in the Measurements tab, we select the Sound Level, and on the sending device, in the Tools tab, we select the Synthesizer, set to 1000 hertz. Using the transmitting device, the location of the microphone is sought by detecting the maximum sound intensity.
Now let's experiment. On a rug, carpet or better still a sound insulator, place the two devices facing each other, with the speaker of the transmitter exactly in front of the microphone of the receiver. We launch the synthesizer with a sufficiently strong volume, and we remove the transmitter at a distance such that the sound volume is 105 db. The distance between the two smartphones is measured. Now we move the transmitter away so that the volume is 90 db. What is this new distance? What is the ratio of these distances? How far away should Emma be from the enclosure? Theory shows us that when we double the distance the sound level is reduced by 6 decibels, does the experiment confirm this calculation?
To learn more about the cancellation of sound waves, you can download the activity "Chloé at the concert".
Measure the speed of sound
There are several methods for calculating the speed of sound using a laptop. Here we are going to carry out an original experiment to calculate this speed using our frequency synthesizer. This experiment is carried out with an Android device which allows at the same time to emit a sound and to analyze its sound level.
For this experiment you will need a thick book, a ruler, and a small paperback book with a reflective cover. On a rug or carpet, or better a sound insulator, place the laptop on a book laid flat so that it is a bit high. Then we emit a sound of 680 hertz frequency with the synthesizer of the Tools menu and simultaneously we analyze the Amplitude of the signal with the Measurement Oscillogram. Place the pocket book vertically in front of the smartphone, then move it aside until the amplitude measurement is as low as possible. The distance between the smartphone and the book is then measured. This measurement allows us to calculate the speed of sound by the formula: speed of sound = frequency*4*distance(cm)/100
Why does this experiment allow us to calculate the speed of sound? The sound level at the microphone is the sum of the sound wave coming from the loudspeaker and the wave reflected by the book. The intensity of this second wave is weak but sufficient to create a small variation in volume at the level of the microphone by interference with the main wave. When the book is placed at a quarter of the wavelength, the reflected wave is out of phase by half a period with respect to the emitted wave, and therefore reduces the intensity of this wave at the level of the microphone, close to the loudspeaker.
This experiment generally leads to an overestimation of the speed of sound. Indeed, we assumed that the microphone and the loudspeaker were in the same place. In practice they can be separated by a few centimeters. On the other hand, the microphone itself is not placed on the surface of the smartphone, from where we take the measurements. The calculation of the speed is not very precise but the concept is very attractive!
The synthesizer is a very useful tool to conduct innovative experiments on all the fields of sound. Having three tracks is useful to be able to conduct in depth analysis. FizziQ synthesizer is complemented by a Sound Library where one can find over 20 different sound to conduct experimentation on a variety of subjects like white noise, bell sound, Doppler effect, echolocation, and more.