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Hear like a dog - electronic ear protection modification

Leto1984

Oct 31, 2021
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Hello! I have a question.
Two years ago my electronic earmuff malfunctioned and I heard some weird stuff while out hunting. It's stuck with me. I would like to modify my earmuffs so that I can hear the high and low frequencies outside of my hearing range. How can I do this? I know the earmuffs just cut off the sound when it reaches a certain decibel input to the mic. Can I build a circuit between the mic and the cutoff that will lower the high frequencies and raise the low frequencies into my hearing range? Can someone tell me how? I have a pair of earmuffs I can cut up and I'm willing to solder something together and give it a go! Thanks in advance!
 

Nanren888

Nov 8, 2015
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Not sure I'd expect much of interest in the low frequencies.
Pages such as
https://www.homemade-circuits.com/ultrasonic-receiver-circuit-extend-your-ears-sensitivity/
show attempts to let you hear ultrasonic ranges.
This one seems to mix the higher spectrum down into the audible range.
Have not looked at this one, so cannot vouch for it.
.
One issue to be aware of, is that when you shift frequencies up and down, you tend to ruin the harmonic relationships. In summary, in a sense you make them sound different, if that makes sense, for something that you can't hear. Things that used to be related to make complex noises, of multiple related pitches, loose their natural pitch relationships.
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Another approach, pitch shifting, is to sample fast & playback more slowly. Basically scaling things in time, so harmonics are still harmonics. Problem is that things now take longer, so can't run continuously & flawlessly in real time.
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May not have been out of band frequencies you heard that time.
Enjoy.
 

Leto1984

Oct 31, 2021
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Thanks Nanren! I did some other digging and was given this paper yesterday:

Ultrasonic Listener
Microcontroller Based Frequency Shifter

A Senior Project
presented to

the Faculty of the Electrical Engineering
California Polytechnic State University, San Luis Obispo

In Partial Fulfillment
of the Requirements for the Degree
Bachelor of Science

by
Troy Fredriks

7 June 2010
© 2010 Troy Fredriks

I'm not sure if I can post it here due to copyright but i can tell you it uses a mocrocontroller and looks much more complicated than this solution. Is there a website or tool that will allow me to translate the circuit diagram from your link into a board?

Thanks for your input! I'll be sure to check out that website as well. :)
 

Nanren888

Nov 8, 2015
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The pdf you suggest by Troy Fredriks is implementing the multiplier in a micro. Other than that the approach is similar. The micro means he can choose the frequency range, rather as you could if you changed the frequency of the oscillator in U1a of the linked circuit.
That work does point out something else, I should have mentioned; he uses an ultrasonic transducer as the microphone. If you want to do this, you will need some sort of microphone that will work over the bands you are interested in.
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Not sure which CAD package is the best one as a starter if you want to make a board. With (near) audio circuits you should be able to mock them up on a number of different prototyping systems including vero board, or go to a custom board.
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Might be worth a search round for other circuits online. That was just the first I hit. It should give you some keywords to include in the search.
 

Leto1984

Oct 31, 2021
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Awesome! How would I calculate the frequency base of U1a for say, 10-12hz?
I have a copy of solidworks. I think it has an electronic board design plugin.
Reading yesterday I found that most typical inexpensive microphones will actually pick up frequency below 20hz - most low frequency waves are transmitted through the ground etc. so I wouldn't have to go too much lower to get what I'm after (Animal hearing). I purchased a cheap "bat listening device" which uses ultrasonic transducers. I can look at the board on that one and get some visual understanding. This is coming together :)
As always thanks for you input! I greatly appreciate it!
 

Audioguru

Sep 24, 2016
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I am old and have hearing aids because I have normal-for-my-age high frequency hearing loss.
Originally the transducers were in my ear canals with soft inserts that pass sounds causing squealing feedback when the high frequencies were boosted as much as what my hearing loss needs.
A feature of the hearing aids is to convert all high frequencies to an octave lower so that the boost is not needed to be as much. But it sounded weird and awful. That feature was turned off and I got firm molds to hold the transducers in my ear canals that do not cause feedback squealing.

At work a popular little speaker produced no low frequencies so I developed a circuit that converted low frequencies up one octave and the little speakers sounded much better with the circuit. These sounds were music and speech sounds, not earth vibrations.
 

Leto1984

Oct 31, 2021
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I am old and have hearing aids because I have normal-for-my-age high frequency hearing loss.
Originally the transducers were in my ear canals with soft inserts that pass sounds causing squealing feedback when the high frequencies were boosted as much as what my hearing loss needs.
A feature of the hearing aids is to convert all high frequencies to an octave lower so that the boost is not needed to be as much. But it sounded weird and awful. That feature was turned off and I got firm molds to hold the transducers in my ear canals that do not cause feedback squealing.

At work a popular little speaker produced no low frequencies so I developed a circuit that converted low frequencies up one octave and the little speakers sounded much better with the circuit. These sounds were music and speech sounds, not earth vibrations.
Do you have a circuit schematic for this? It sounds like exactly what I'm trying to do!
 

Nanren888

Nov 8, 2015
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My words above and the project by Troy Fredriks shift frequency bands, down to shift high frequiencies into audible range. Hence the need for an ultrasonic microphone. The range doesn't get larger or smaller, just shifted.
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You can rearrange these to shift upwards instead, butgenerally have to select the amount to shift & the direction, not both directions at the same time, sensibly. From memory, people can't hear 50Hz; when we hear a 50Hz hum, I understand it's usually the harmonic at 100 we are hearing. Also, if you shift frequencies as low as 10Hz into the audio band the harmonic relationships will be quite broken. The shapes will be quite distorted.
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The mixer-based systems have a bit of theory behind them, as in the mini-thesis.Maybe try giving it a read through. You could also google modulation and mixers. They multiply the signals waveforms together. If I have a sound component at frquency fs and an oscillator frequency of fo, then the resulting multiplied signal has components at fs-fo and fs+fo, as in the thesis. As Troy was mixing downward, he filters off the higher one that he doesn't want to hear and is left with the shifted-down one. So the oscillator is set to the amount you want to shift by. All the components in the signal shift, so a range of spectrum [flow,fhigh] shifts to [flow-fo,fhigh-fo] and also to [flow+fo,fhigh+fo], then you filter out the band you didn't want. So, non-trivial to design, sorry.
If you don't want to go the micro-way, you could have a switch to select the oscillator frequency, the amount to shift by, and filter for what ended up in the audio band.
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To hear low frequencies, proper pitch shifting, scaling of the band, might be better. As the higher frequencies are likely a lot louder, probably need to filter those out before scaling it.
THere are lots of sources of noise at low frequencies, such as movements that might swamp any signal that you are wanting to pick up.
 

Audioguru

Sep 24, 2016
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From memory, people can't hear 50Hz; when we hear a 50Hz hum, I understand it's usually the harmonic at 100 we are hearing. Also, if you shift frequencies as low as 10Hz into the audio band the harmonic relationships will be quite broken. The shapes will be quite distorted.
No. Humans can hear from 20Hz to 20kHz. Cheap little speakers cannot produce 50Hz or less, instead they produce nothing or produce 100Hz and higher harmonics.

One octave higher can produce harmonics that are also one octave higher. The relationships are not broken.
 

Nanren888

Nov 8, 2015
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Sorry, I was obviously not clear.
The context is shifting bandpass signals with a mixer. If I shift a signal with inaudible components at 10Hz, 20Hz, 30Hz, 40Hz to an audible range, say 1010Hz, 1020Hz, 1030Hz, 1040Hz the harmonic relationships are broken.
 

73's de Edd

Aug 21, 2015
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Go analog and investigate trying this . . . . .
https://www.nutsvolts.com/magazine/article/june2011_berber

et

https://nutsvolts.texterity.com/nutsvolts/201106/?folio=30&pg=30#pg30

Caveat . . . . . If so using, triple check his VERO board layout / wiring against the actual schematic !
And read all of the reader / builders comments as to same.
As for myself, that lowest 3 VDC, supply spec might only work with some brands of '324's.
I would feel better with +5 VDC on upwards, whereas, it might become a fire breathing dragon at 9 VDC.
 
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Audioguru

Sep 24, 2016
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I noticed that the article did not include a recording of the lousy old LM324 quad opamp producing only low frequency noise.
Google has many videos that play bat sounds at frequencies that we can hear. The sounds are just noises.
 
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