When you press and immediately release (click) the Filter button on the Thinklabs One, the device is designed to alternate between two favorite filters, analogous to Bell and Diaphragm on a conventional stethoscope. The LEDs on the Hz scale indicate the filter pitch, as shown in the image to the left. Lower pitch filters for heart sounds appear to the left side of the scale, and higher pitch filters appear to the right side of the scale. If all LEDs are lit, the One is using the full bandwidth filter (entire frequency range).

However, you may press the Filter button only to find the LEDs remain fixed in the same location. Fortunately, the One is working perfectly, the issue is minor, and the solution is a simple one. Both favorites have been set to the same filter. In other words, pressing the Filter button alternates between two favorites set to the same filter setting. The resolution is to select a different filter for at least one of the favorites. For more information on setting favorites, click here.