diff --git a/src/main.rs b/src/main.rs
index 8e3553f..03704d6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,6 +3,8 @@ use std::{fs, io::{stdout, Write}};
 use midly::Smf;
 
 const FILENAME: &str = "media/TOUHOU - Bad Apple!!.mid";
+const STEP: u32 = 96;
+const TRACK: usize = 0;
 
 fn get_u32(bits: &[bool; 32]) -> u32 {
     let mut result = 0u32;
@@ -20,33 +22,47 @@ fn main() {
 
     let mut stdout = stdout();
 
-    let mut current_on = [false; 32];
+    let mut current_on_upper = [false; 32]; // higher notes
+    let mut current_on_lower = [false; 32]; // lower notes
 
-    let track = &smf.tracks[0];
+    let track = &smf.tracks[TRACK];
     for (_, event) in track.iter().enumerate() {
+        // println!("{}", event.delta);
         let mut delta = event.delta.as_int();
-        while delta >= 96 {
-            delta -= 96;
-            let word = get_u32(&current_on);
-            stdout.write(&word.to_le_bytes()).ok();
+        while delta >= STEP {
+            delta -= STEP;
+            let upper_word = get_u32(&current_on_upper);
+            let lower_word = get_u32(&current_on_lower);
+            stdout.write(&upper_word.to_le_bytes()).ok();
+            stdout.write(&lower_word.to_le_bytes()).ok();
         }
         match event.kind {
             midly::TrackEventKind::Midi { channel: _, message } => match message {
                 midly::MidiMessage::NoteOff { key, vel: _ } => {
-                    let index = key.as_int() as isize - 59;
-                    if index >= 0 && index < 32 {
-                        current_on[index as usize] = false;
+                    let key_i = key.as_int() as usize;
+                    if key_i >= 59 && key_i <= 90 {
+                        current_on_upper[key_i-59] = false;
+                    }
+                    if key_i >= 27 && key_i <= 58 {
+                        current_on_lower[key_i-27] = false;
                     }
                 }
                 midly::MidiMessage::NoteOn { key, vel: _ } => {
-                    let index = key.as_int() as isize - 59;
-                    if index >= 0 && index < 32 {
-                        current_on[index as usize] = true;
+                    let key_i = key.as_int() as usize;
+                    if key_i >= 59 && key_i <= 90 {
+                        current_on_upper[key_i-59] = true;
+                    }
+                    if key_i >= 27 && key_i <= 58 {
+                        current_on_lower[key_i-27] = true;
                     }
                 }
-                _ => {}
+                _ => {
+                    // println!("event {}: {:?}", i, message);
+                }
             },
-            _ => {}
+            _ => {
+                // println!("event {}: {:?}", i, event);
+            }
         }
     }
 }