Converting file to sub audible frequencies

I’m new here and a relatively new user to Audacity. I’m trying to convert recorded files to below 20Hz (Infra Sound) to play through a bass shaker driver. I’m recording at a rate of 8000Hz then going to the effects menu, selecting pitch and tempo*, then change pitch and changing the value to 20Hz and below. When I play the files back through the computer speakers I can hear the file even though its below the range of human hearing and shouldn’t be able to hear anything. Also worth noting when I play a pure sine wave, at a single infrasound frequency, through the same driver at the same levels from the source and power amplifier it’s much stronger.

Change pitch is a percentage of the original. You can type-in “from 1000 to 500” or “from 40 to 20” and you’ll get the exact-same results.

Depending on what frequencies you have in your original effects you can low-pass filter at 40 Hz to kill everything above 40Hz. Then pitch shift by -50% and the highest remaining frequencies will be around 20Hz.

Note that filters aren’t “perfect” and there is a slope. And no matter no matter what the steepness the cutoff frequency is defined as the -3dB point. i.e. With a 40Hz cutoff, there is still something at 41Hz.

It’s not unusual to hear distortion components from the amplifier or speaker.

At the same peak level, it will be… I don’t know about your “effects” but normal voice or music has an average level around 10-20dB below the peak and our perception of loudness is more-related to the short-term average. A square wave can go louder… A square wave (of the same peak) contains twice as much energy and that energy is all higher frequency harmonics which are “easier to hear” than low frequencies.

Run the Normalize or Amplify effect to normalize (maximize) the volume as the last-step before exporting.

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