Human ears can hear 20 – 20000hz frequency, if you were to listen one of those [frequency test videos](https://www.youtube.com/watch?v=PAsMlDptjx8) they go from very low pitch to very high, then how exactly do these sounds represent different instruments in songs or voices? I messed around with with EQ in DAWs and they depict that different instruments hit on different frequencies in the spectrum yet they sound so different from the video?
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Well a test frequency usually uses a sine wave. This is a very basic wave where the characteristic shape is fully described by a single frequency.
Almost all sounds – voice, instruments etc – are a combination of various frequencies at different amplitudes (aka loudness). Even if a (say) guitar makes a note with a fundamental frequency (the loudest note), it also produces other sounds at other frequencies (called harmonics). This makes a guitar “sound” like a guitar. This is why different instruments and voices singing the same note have different qualities.
Frequency is not a thing by itself is just how many times something happens per unit of time.
The frequency of your birthday is 1 per year. Hertz is just cycles per second.
Sound is a pressure wave in the air and if has 5000 cycles per second it had a frequency of 5000hz. So you do not turn frequency into sound, the sound is a pressure wave in the air, frequency is a description of how many cycles per second a pressure wave has.
You compare it to waves you create in water. If you have a large container and move a ball up and down in it you create the wave. Move the ball up and down twice per second and the waves have a frequency of 2 Hz. The frequency is a description of the wave not a thing in itself.
So you do not turn frequency int sound, the frequency it one way we describe the sound. You can compare to how you can describe fabric by the thread count in the number of threads per inch. That is like frequency but for distance instead of time. You do not make fabric from thread count the same way does not make sound from frequency, both its way to describe fabric and sound.
Any periodic wave can be broken down into simple sin waves and the spectrum of a sound is a representation of what sine waves it is made up off.
It’s not meant to represent anything or any sound in particular, it’s bunch of different frequencies being played in sequence, it’s pure tones that you don’t really hear normally, music instruments don’t sound like that, they sound like many different frequencies played together. However pure pitches like this can be useful to test how well your stereo or your hearing works on various frequencies
Side note: YouTube can’t really reproduce sounds above 16000 Hz or so, so it’s not really a good test anyways
To dive deeper, mess around with a spectrogram. You can find such a function in free audio software like audacity – or anywhere now, really. It breaks a waveform into a frequency intensity over time image.
When you play a recording of an instrument, note the various frequencies that are layered together. Some of those are harmonics (frequencies that are a multiple of the base frequency – octaves), others are resonant frequencies (frequencies generated by an object as the vibrations match the speed sounds travels in the object – like those made from rubbing the rim of a glass) of the instrument that are generated from the shape and composition of the instrument, and any strings that are excited through sympathetic resonance (the frequencies are the same as the note the string is tuned to) as well.
This is why a piano playing A440 produces a much more complex sound than a single 440Hz tone, and also sounds different from other tonal instruments like woodwinds or strings.
Now, being able to hear all frequencies in a basic hearing test means you’ll hear more of the sound than someone with hearing loss. Loss of sensitivity to a few frequencies won’t be noticeable, but serious damage from exposure to loud sounds or explosions, or head injury will result in missing out on a lot. If the loss is in the low range – 300-3000 Hz, you’ll likely miss conversations and music will sound tinny.
Protect your ears: your future self will thank you.
Try looking up the “frequency spectrum/response” of an instrument.
Horns will be different from woodwinds, which will be very different from a piano.
The proportion of high and low octaves of an instrument determine the “musical sound” or “tambre”.
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