diff --git a/nemu/src/device/audio.c b/nemu/src/device/audio.c
index 11fe2c9..0fb22f1 100644
--- a/nemu/src/device/audio.c
+++ b/nemu/src/device/audio.c
@@ -38,15 +38,16 @@ static void audio_callback(void *userdata, uint8_t *stream, int len) {
   uint32_t read_cnt = MIN(count, len);
   uint32_t to_end_cnt = audio_base[reg_sbuf_size] - pos_read;
   int32_t out_bound_cnt = read_cnt - to_end_cnt;
+  memset(stream, 0, len);
   if (out_bound_cnt > 0) {
-    SDL_memcpy(stream, sbuf + pos_read, to_end_cnt);
-    SDL_memcpy(stream + to_end_cnt, sbuf, out_bound_cnt);
+    memcpy(stream, sbuf + pos_read, to_end_cnt);
+    memcpy(stream + to_end_cnt, sbuf, out_bound_cnt);
   } else {
-    SDL_memcpy(stream, sbuf + pos_read, read_cnt);
+    memcpy(stream, sbuf + pos_read, read_cnt);
   }
   pos_read += read_cnt;
   pos_read %= audio_base[reg_sbuf_size];
-  if (len > read_cnt) SDL_memset(stream + read_cnt, 0, len - read_cnt);
+  // if (len > read_cnt) memset(stream + read_cnt, 0, len - read_cnt);
   audio_base[reg_count] -= read_cnt;
 }