diff --git a/GB_set_highpass_filter_mode.md b/GB_set_highpass_filter_mode.md
index fdf1fb6..81540c5 100644
--- a/GB_set_highpass_filter_mode.md
+++ b/GB_set_highpass_filter_mode.md
@@ -9,14 +9,22 @@ typedef enum {
 } GB_highpass_mode_t;
 ```
 
-<tt>void GB_set_highpass_filter_mode([[GB_gameboy_t]] *gb, [[GB_highpass_mode_t]] mode);</tt>
+<tt>void GB_set_highpass_filter_mode([[GB_gameboy_t]] *gb, GB_highpass_mode_t mode);</tt>
 
 In `apu.h`
 
 ## Description
 
-TBD
+A real Game Boy has its audio output going through a high-pass filter before reaching the built-in speaker or headphones, which removes the variable DC-offset the digital output generates. This function controls the high-pass filter the emulator instance uses:
+
+* `GB_HIGHPASS_OFF`: No high-pass filter is used, the DC offset remains
+* `GB_HIGHPASS_ACCURATE`: A simple high-pass filter is applied; this setting best represents the hardware behavior
+* `GB_HIGHPASS_REMOVE_DC_OFFSET`: The DC offset is separated from the actual wave form, and a simple high-pass filter is only applied to the DC offset part
 
 ## Thread Safety
 
 `GB_set_highpass_filter_mode` is thread-safe and can be called from any thread and context.
+
+## Notes
+
+Keep in mind that the DC offset is not constant prior to applying the high-pass filter.
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