diff --git a/Core/apu.c b/Core/apu.c
index c74bb6d..4e417d7 100755
--- a/Core/apu.c
+++ b/Core/apu.c
@@ -27,11 +27,11 @@ static void update_sample(GB_gameboy_t *gb, unsigned index, uint8_t value, unsig
     if (gb->apu_output.sample_rate) {
         unsigned left_volume = 0;
         if (gb->io_registers[GB_IO_NR51] & (1 << index)) {
-            left_volume = gb->io_registers[GB_IO_NR50] & 7;
+            left_volume = (gb->io_registers[GB_IO_NR50] & 7) + 1;
         }
         unsigned right_volume = 0;
         if (gb->io_registers[GB_IO_NR51] & (0x10 << index)) {
-            right_volume = (gb->io_registers[GB_IO_NR50] >> 4) & 7;
+            right_volume = ((gb->io_registers[GB_IO_NR50] >> 4) & 7) + 1;
         }
         GB_sample_t output = {(0xf - value) * left_volume, (0xf - value) * right_volume};
         if (*(uint32_t *)&(gb->apu_output.current_sample[index]) != *(uint32_t *)&output) {
diff --git a/Core/apu.h b/Core/apu.h
index bace09a..44b3d45 100644
--- a/Core/apu.h
+++ b/Core/apu.h
@@ -6,9 +6,9 @@
 
 
 #ifdef GB_INTERNAL
-/* Divides nicely and never overflows with 4 channels and 8 volume levels */
-#define MAX_CH_AMP 0x1FFE
-#define CH_STEP (MAX_CH_AMP/0xF/7)
+/* Divides nicely and never overflows with 4 channels and 8 (1-8) volume levels */
+#define MAX_CH_AMP 0x1FE0
+#define CH_STEP (MAX_CH_AMP/0xF/8)
 #endif
 
 /* APU ticks are 2MHz, triggered by an internal APU clock. */