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To test the frequency range of your earphones, you can play a song with a variety of pitches. Listen carefully for the low sounds, such as those from bass guitars or baritone vocals. These tones should sound deep but crisp and rich.  Some earphones can detect frequencies as low as 20 hertz (Hz). Check the packaging for more information. If all headphones seem to have the same frequency issues, your hearing could be the issue. Balanced earphones pick up high frequencies as well as low frequencies. High frequencies occur in orchestral arrangements and other music. Try listening to music with high-pitched voices, guitars, piccolos, and other instruments to make sure these tones come through the earphones without distortion.  Good earphones can detect frequencies as high as 20 kHz. Earphones may detect either high or low frequencies better. If this happens, choose earphones that are best for the content you listen to. To test the dynamic range, change the volume so the audio plays loudly but doesn't make you uncomfortable. The dynamic range indicates how loud and soft the audio can get before you stop hearing it. You should be able to hear the full range of sound clearly at a comfortable volume. For instance, if you listen to a lot of podcasts, you may need your earphones to pick up low voices rather than high-pitched instruments. . Flatness is when low, medium, and high-pitched sounds all have the same audio quality. Try playing a song that transitions between various pitch levels. If the earphones seem to pick up higher tones much better than lower tones, the music probably won’t sound that great to you. Good earphones maintain a consistent audio quality no matter how high or low a tone is.  Fatness doesn’t mean the music lacks dynamic highs and lows. This test is subjective. It can change depending on your hearing. Find earphones that work best for you personally. Keep the audio at a high but comfortable level and listen closely. You have probably heard unpleasant sounds blasting from a car radio before. Bass-heavy music often sounds unpleasant because the electronics cannot relay the sounds cleanly. No one enjoys having that buzzing sound in their ears.  The audio should sound clear no matter what plays. Usually, newer, costlier earphones have less issues with rattling than older, cheaper earphones. Rattling may not be an issue if you don’t listen to a lot of music with low pitches. The best earphones are immersive, making you feel like you’re at a concert or listening to someone speak in person. For this to happen, the audio needs to be full and rich. Any distortion not only sounds unpleasant, but reminds you you’re wearing earphones.  If you can, use binaural recordings to test this. These sounds are recorded with microphones placed on the ear, so they are ideal tests of immersion. For example, listen to binaural audio of someone knocking on a door. Ask yourself if it sounds like someone is knocking on a real wooden door right next to you.

Summary:
Play low-frequency sounds to make sure they are audible. Listen to high frequencies to gauge how well the earphones detect them. Adjust the sound volume to hear the dynamic range. Test the earphones for an even sound quality at all pitches. Check the audio for any signs of buzzing or rattling. Gauge how realistic the sound is in your ears.