Ultrasound, a realm beyond human hearing, offers a captivating window into a world often overlooked. These high-frequency sound waves, ranging from 20 kHz to 20 MHz, hold secrets waiting to be unveiled. With the right equipment and techniques, you can transform these inaudible vibrations into an auditory experience.
Essential Gear for Ultrasound Exploration
To capture and analyze ultrasound, you’ll need (somewhat) specialized equipment:
- High Sample Rate Recorder: Devices capable of recording at 192 kHz, such as the Zoom H6 Handy Recorder, are ideal. This sample rate allows for the capture of frequencies up to 96 kHz, providing a broad spectrum for ultrasonic exploration. When you record with a sample rate of 96 kHz, you can receive signals up to 48 kHz.
- Ultrasonic Microphone: A microphone specifically designed for high frequencies is crucial.
Our Cortiça Microphone, with its high sensitivity is a prime example. - Computer and Audio Software: A computer with audio editing software like Audacity or Adobe Audition is essential for manipulating and analyzing recorded data.
The world is replete with ultrasonic phenomena. Animals, from bats navigating the night sky to dolphins communicating underwater, rely on ultrasound for survival and interaction. Industrial processes, from the hum of power lines to the operation of machinery, often produce ultrasonic emissions that can indicate equipment health or environmental impact. Even the flow of fluids and the workings of electronic devices generate ultrasonic signals, offering insights into their behavior and potential issues. These hidden sound worlds, once captured and analyzed, hold a wealth of information waiting to be discovered.
The Art of Ultrasound Recording
To capture these elusive sounds, consider the following techniques:
Microphone placement is crucial for optimal ultrasound capture. While an omni electret microphone picks up sound equally from all directions, positioning it as close to the sound source as possible is essential to maximize signal-to-noise ratio. For distant sources, consider using a directional microphone to isolate the target sound. To minimize background noise, record in a quiet environment or employ noise-canceling techniques during post-processing. Experimenting with different microphone angles can significantly impact the recorded signal, so try various positions to optimize capture. Lastly, calibrating your equipment using a known ultrasonic source ensures accurate frequency measurements and reliable data collection.
Transforming the Invisible into Audible
Once you’ve captured your ultrasound recordings, it’s time to bring them to life. By reducing the playback sample rate in audio editing software, you can shift the high frequencies into the audible range. For instance, a 45 kHz bat call recorded at 192 kHz can be slowed down to 3.75 kHz by setting the playback rate to 16 kHz. This process, similar to slowing down a vinyl record, allows you to hear the previously inaudible sounds.
Step-by-step:
To begin, configure your recorder to the highest possible sample rate, ideally 192 kHz, and set microphone gain as usual. Remember, microphones become directional at ultrasonic frequencies, so point it directly at the sound source. Record your target, though you won’t hear the ultrasonic content. Open the recording in Audacity and reduce the playback sample rate to around 16 kHz to bring the ultrasound into the audible range. Experiment with different settings to find the best result. When exporting, reduce the project sample rate to a standard like 44.1 or 48 kHz to avoid large file sizes, but ensure it’s not lower than the track sample rate.
To delve deeper into ultrasound exploration, consider these advanced techniques:
- Spectrogram Analysis: Visualize the frequency content of your recordings over time to identify patterns and characteristics.
- Filter Design: Create custom filters to isolate specific frequency bands within the ultrasonic spectrum.
- Data Analysis: Use statistical and machine learning techniques to extract meaningful information from your recordings.
By combining the right equipment, careful recording techniques, and creative audio processing, you can unlock the hidden world of ultrasound and discover a universe of sound waiting to be explored.
Here are our latest exploits recording bats, circling around the Sonic Artefacts workshop:
Made some ultrasonic recordings with the Cortiça Microphones? Please share them with us!
