diff --git a/papers/doc/7-systems/k007232.md b/papers/doc/7-systems/k007232.md
index 92b4759c4..1e5dc7684 100644
--- a/papers/doc/7-systems/k007232.md
+++ b/papers/doc/7-systems/k007232.md
@@ -4,6 +4,8 @@ a Konami's 2 channel PCM sound chip was used in their arcade boards in 1986-1990
 
 Its sample format is unique; the topmost bit is the end marker, and the low 7 bits are used for generating sound (unsigned format).
 
+It has 7 bit digital output per each channel and no volume register on chip, so it needs external logic to control channel volume.
+
 # effects
 
 - Nothing for now