diff --git a/doc/7-systems/nes.md b/doc/7-systems/nes.md
index 4837df48b..c3ccb7064 100644
--- a/doc/7-systems/nes.md
+++ b/doc/7-systems/nes.md
@@ -6,7 +6,8 @@ also known as Famicom. it is a five-channel sound generator: first two channels
 
 # effects
 
-- `11xx`: **write to delta modulation counter.** range is `00` to `7F`. this may be used to attenuate the triangle and noise channels down to about half normal volume.
+- `11xx`: **write to delta modulation counter.** range is `00` to `7F`.
+  - this may be used to attenuate the triangle and noise channels; at `7F`, they will be at about 57% volume.
   - will not work if a sample is playing.
 - `12xx`: **set duty cycle or noise mode of channel.**
   - may be `0` to `3` for the pulse channels: