how to make low frequencies MORE audible

[jac]

Hi,

I’m trying to make low frequencies (20Hz-300Hz) MORE audible.
I connected a Behringer ECM8000 measurement microphone to a Roland R-26 field recorder.
I’m visualising (via a waterfall diagram and spectrum graph) the real-time signal measured with the ECM8000 via the audio interface of the R-26 with audio spectrum analyser software.
Simultaneously while visualising, i’m (analog mono) recording a short maximum 1.5 minute track on the R-26 itself.
The recording format is 16-bit WAV.
The sample rate is 44.1 kHz.

I attached an original (un-edited) recorded 5sec WAV file and an edited (normalized, equalized, pitched) 5sec OGG file.
One should hear noise (between 20Hz-60Hz) and (for low frequency testing purpose) very short jumping on the floor (between 40Hz-160Hz).
How to make the very low frequencies (for testing purpose short jumping on the floor) MORE audible?

Regards,
jac

Audacity version number: 2.1.0
Windows 7 x64 SP1

[kozikowski]

What's the job? Sometimes we can get an idea of the solution by knowing what the eventual goal or product is. For example, you probably didn't getup this morning thinking, "I think I'll jump on the floor today."

Koz

[jac]

Hi,
>>What's the job?

I want to make for the city counsel, housing association, etc. (MORE) audible low frequencies sounds, which can be caused by (vibration of) central heating, traffic, etc.

Regards,
Jac

[cyrano]

How to make the very low frequencies (for testing purpose short jumping on the floor) MORE audible?

The first thing that springs to my mind is "getting better/bigger speakers"

Be aware that room measurements are fine over 850 Hz or so. Below you are not measuring your speakers, but your room.

And if you have bass problems with decent sized speakers you might need room treatment.

Also, a 5" woofer really can't reproduce 80 Hz at any audible level. What you're hearing is probably 160 Hz and your brain is translating it to the base tone.

[steve]

A simple test.

Generate a "chirp" (in the Generate menu), with these settings:
Start frequency: 300 Hz
Start Amplitude: 0.8
End Frequency 20 Hz
End Amplitude; 0.8
Interpolation: Logarithmic
Duration 30 seconds

Play the track. Can you hear the sound right down to 20 Hz?

[jac]

Hi,

Thanks for the test. I generated the Chirp. I can hear the first 5-10 sec.
With which (a-brands) bass headphones could one hear, at an audible level, the sound right down to 20Hz?

Regards,
Jac

[steve]

With which (a-brands) bass headphones could one hear, at an audible level, the sound right down to 20Hz?

"Ears" are terrific at detecting sounds between around 200 Hz to 12000 Hz, but beyond that range they are less sensitive. A child with really good hearing may be able to hear sounds clearly up to around 16000 Hz, and "detect" sounds up to almost 20000 Hz. With age, hearing tends to become less acute, particularly for high frequencies, such that for most adults the upper limit is usually around 16000 Hz if you're lucky.

At the extreme low end, "ears" are not very good at hearing, but other parts of the body can detect the vibrations which the brain interprets as very low sound - thus for very low frequencies you not only hear with your ears, but with your whole body.

The intensity of sound is technically called "Sound Pressure Level" (SPL). Over the normal hearing range, SPL approximately correlates to "loudness" (how "loud" it sounds is the subjective sensation). In order to hear sounds in the extreme low frequency range with your ears, the Sound Pressure Level needs to be so high that it is likely to cause permanent hearing damage.

To hear sounds down to 20 Hz, you really need some very large speakers that can move enough air so that your body can "hear" it.

sub-woofer.png (232.34 KiB) Viewed 2318 times

[jac]

Hi,

Thank you for the information and visualisation.
Former reaction explains why one can’t hear/detect the “very short jumping on the floor” in the original (un-edited) recorded 5sec WAV file.
One can hear/detect and visualise (via a waterfall diagram and spectrum graph) the “very short jumping on the floor” in the edited (normalized, equalized, pitched) 5sec OGG file.

What kind of experience do you have (for measurement purposes) with, improvement of the hear ability/detectability of low frequencies (e.g. 20-300Hz), e.g.:
-which frequency shifting, noise reduction or other editing techniques parameters;
-which subwoofer;
-which (class 2) measurement microphone (instead of the used ECM8000);

What kind of experience do you have (for measurement purposes) with, improvement of the visibility of low frequencies (e.g. 20-300Hz), e.g.:
-which (class 2) sound pressure level meter (with datalogging functionality);
-which filter parameters for audio spectrum analyser software;

kind regards,
Jac

[steve]

If you want "scientific" data, then probably best to go to an industrial noise specialist. They will have all of the right equipment for measuring and logging low frequency noise (a common problem in heavy industry).

For "non-scientific demonstration" purposes, the ECM8000 should work reasonably well, provided that your pre-amp does not filter out very low frequencies.
I'd record the sound, then use the Equalization effect to reduce frequencies above 200 Hz.

Screenshot.png (40.64 KiB) Viewed 2310 times

Then Normalize to about -3 dB.

Then use the "Change Speed" effect and type 10.0 as the "Speed Multiplier" http://manual.audacityteam.org/o/man/change_speed.html (requires a recent version of Audacity).
This will make the track play 10 times faster, and will increase the frequencies x10, so that 20 Hz becomes 200 Hz and 200 Hz becomes 2000 Hz (much easier to hear).