This is Burn-in Audio, which specializes in Low-Mids.
When you feel that a sound is "muddy," you may think that it is because the high frequencies are weak. However, the cause is more likely to be in this frequency band where sound congestion tends to occur.
🎧 Volume setting
First set the volume to low.
When the main program starts, please turn up the volume a little at a time. Set the volume just before the sound becomes distorted.
After adjustment, please remove the earphones from your ears.
The time it takes for changes to occur varies from device to device. If you do not feel any change, please try several times.