diff --git a/mainmem.audio.s b/mainmem.audio.s
index 26e59d0..5661d09 100644
--- a/mainmem.audio.s
+++ b/mainmem.audio.s
@@ -1,7 +1,10 @@
 * MAINMEM.AUDIO.S
 * (c) Bobbi 2022 GPLv3
 *
-* Applecorn audio code
+* Applecorn audio code.
+* This is the implementation of the audio-engine.  The code is
+* device-independent, using the Ensoniq driver in MAINMEM.ENSQ.S
+* or the Mockingboard driver in MAINMEM.MOCK.S.
 *
 
 SYSCLOCK     DB    $00                       ; Centisecond counter (5 bytes)
@@ -729,6 +732,7 @@ ADSRPHASE   STX   OSCNUM
 :S1         TYA                             ; Change/step -> A
             CLC
             ADC   CURRAMP,X                 ; Add change to current amp
+            BCS   :CLAMP                    ; If overflow, clamp to target
             CMP   :TARGET                   ; Compare with target
             BCS   :CLAMP                    ; If target < sum, clamp to target
             BRA   :UPDATE                   
@@ -739,6 +743,7 @@ ADSRPHASE   STX   OSCNUM
 :S2         TYA                             ; Change/step -> A
             CLC
             ADC   CURRAMP,X                 ; Add change to current amp
+            BCS   :CLAMP                    ; If overflow, clamp to target
             CMP   :TARGET                   ; Compare with target
             BCC   :CLAMP                    ; If target >= sum, clamp to target
             BRA   :UPDATE