Changing frequencies of a song to unheard frequencies

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sarel93
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Changing frequencies of a song to unheard frequencies

Post by sarel93 » Thu Jan 11, 2018 4:09 pm

Hello,

Complete newbie here hoping for some help. I have a university project which I am doing which involves Cymatics. I can give a brief explanation of the project for anyone who is interested.

My question is that, can I convert the frequencies of a song to frequencies which cannot be heard e.g in the range of 30-50Hz? Maybe I am phrasing my question wrong but I would be grateful for any help or insight you are able to offer.

Thanks!

DVDdoug
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Re: Changing frequencies of a song to unheard frequencies

Post by DVDdoug » Thu Jan 11, 2018 4:58 pm

My question is that, can I convert the frequencies of a song to frequencies which cannot be heard e.g in the range of 30-50Hz?
The nominal range of human hearing is 20Hz - 20kHz, so 30-50Hz is perfectly audible... Most music contains sounds in the 50Hz range and there may be some content down to 20Hz, depending on the recording.
(Although your woofer/subwoofer may not be able to reproduce those low frequencies.) Did you mean to say 30-50kHz?

You can pitch-shift with Audacity, but that's usually a slight change to change the "key" of a song. I don't know the limits of Audacity, but I don't think you can shift from 20Hz to the ultrasonic range (that's a factor of at least 1000). And if you multiply by 1000 to push 20Hz -> 20kHz, then 20kHz becomes 20MHz which pretty-much impractical for acoustic waves.

Also if you increase the frequency, be aware of the Nyquist Limit for digital audio.
Last edited by DVDdoug on Thu Jan 11, 2018 5:02 pm, edited 1 time in total.

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Re: Changing frequencies of a song to unheard frequencies

Post by steve » Thu Jan 11, 2018 4:58 pm

sarel93 wrote:can I convert the frequencies of a song to frequencies which cannot be heard e.g in the range of 30-50Hz?
The range 30 to 50 Hz is less than an octave. That's hardly enough bandwidth for even a simple tune.
If your audio playback system is capable of going down to 30 Hz, the result will not be inaudible. It will sound like a randomly pulsating very low hum.

Why not just generate some random hum in the required frequency range?
This code can be run in the Nyquist Prompt effect (http://manual.audacityteam.org/man/nyquist_prompt.html) to generate sound in the range 30 to 50 Hz:

Code: Select all

(setf hz 40)
(setf bw 10)
(mult (hzosc hz)
      (lowpass8 (noise) bw)
      16)
9/10 questions are answered in the FREQUENTLY ASKED QUESTIONS (FAQ)

sarel93
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Re: Changing frequencies of a song to unheard frequencies

Post by sarel93 » Thu Jan 11, 2018 6:49 pm

Thank you both for your prompt replies.

Maybe I should give some explanation to what i'm trying to achieve, then maybe you'll understand what it is I am trying to do, because I haven't explained it well in my first post.

I have a large circular plastic lid, of about 70cm diameter and about 4cm deep, sitting atop of a 15inch speaker cone. The lid contains about 3cm of water. If I need to attach any photos/videos to give you a better idea, I can do.

So the whole point of my project is to change some kind of art form (in this case, a song) from something you can hear, into something you can see. So I have a song playing and the ripples show on the water through the vibrations caused.

My question is that, is there any way to make this song still produce these beautiful ripples, without the song being heard? I understand that I might have to just accept there will be some kind of sound in the form of a hum?

Thanks again

Trebor
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Re: Changing frequencies of a song to unheard frequencies

Post by Trebor » Thu Jan 11, 2018 7:10 pm

sarel93 wrote:I have a large circular plastic lid, of about 70cm diameter and about 4cm deep, sitting atop of a 15inch speaker cone. The lid contains about 3cm of water.
Needs to be bassy .... https://youtu.be/Q3oItpVa9fs?t=5m25s

sarel93
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Re: Changing frequencies of a song to unheard frequencies

Post by sarel93 » Thu Jan 11, 2018 7:18 pm

I've managed to produce the frequencies I need which produce the desired effects on the water using an oscillator, but I want to achieve the same water effect but with the variety of different frequencies that a song would have rather than me just having a steady input of the same frequency (unless I change it manually)

DVDdoug
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Re: Changing frequencies of a song to unheard frequencies

Post by DVDdoug » Thu Jan 11, 2018 7:57 pm

A 50Hz low-pass filter will filter-out everything above 50Hz, leaving only the bass. (Use the Classic Filter effect.)

Depending on how much bass energy in the recording, you may want to apply the Amplify effect after filtering.

You are probably going to hear it, depending on how much vibration you need and how far you are from the speaker. And since filters are imperfect, some of the higher frequencies may "leak through".

The sound from the front & back of the speaker will cancel to some extent if you leave the back open. (If you put the speaker in a speaker box "as usual", so the front & rear waves can't mix, you'll get more bass.)

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Re: Changing frequencies of a song to unheard frequencies

Post by kozikowski » Thu Jan 11, 2018 9:33 pm

is there any way to make this song still produce these beautiful ripples, without the song being heard?
I can picture exactly what you want to do, but I can't picture a way of making it silent. You're pumping enough audio energy into a pan of water to move it. That's rough to hide.

I guess you can do it brute force. Mount the speaker system onto a heavy wooden board and then put the whole thing into a box filled with sand or dirt so just the pan and water sticks out. That will go a long way to suppress actual sound.

Then do that frequency filtering listed above.

When you get it running, play a "Gloria in excelsis Deo" by someone recorded in a good cathedral with a killer organ.

You're doing a tiny version of that Las Vegas Fountain thing where a half-acre of pool and fountains follows the music.

Koz

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Re: Changing frequencies of a song to unheard frequencies

Post by kozikowski » Thu Jan 11, 2018 9:35 pm

You are going to shine projector lights onto it during the performance, right? Play it in a dark room with white walls.

Koz

sarel93
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Re: Changing frequencies of a song to unheard frequencies

Post by sarel93 » Mon Jan 15, 2018 7:35 pm

Thanks so much all for your replies, I really appreciate it! I ended up generating a series of low frequencies (lasting about the same length of a song) myself and just looping it.

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