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Fixing rhythm game sync issues when performance drops

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RC

RhythmGame_Creator

Posted on July 16, 2025 • Advanced

🎵 FNF Chart Sync Issues - Notes Going Off Beat!

Hey everyone! I’m working on a Friday Night Funkin’ style rhythm game in Scratch and I’m running into a major synchronization problem that’s driving me crazy! 😤

The Issue:

I’ve got my FNF chart recreation working with arrows/notes that move to the beat, but whenever the game experiences even the slightest lag, everything falls apart:

  • 🎵 Audio stays on time: The music keeps playing at the correct tempo
  • ⬇️ Notes slow down: The arrows/notes start moving slower during lag
  • 💔 Sync breaks: Everything gets completely out of sync with the song
  • 🎮 Gameplay suffers: Players can’t hit notes accurately anymore

My Current Setup:

I’m using these variables to manage timing:

  • Delay-Timer - For timing delays
  • Timer - Main timing variable
  • List scan - For scanning note lists

Here’s my current note movement code:

    when I start as a clone
show

if <(Left-Hold-Note) = [1]> then
switch costume to [Hold]
else
switch costume to (join (Note-Skin) [_])
end

if <(Up-Scroll) = [1]> then
set y to (-180)
else
set y to (180)
end

if <(Up-Scroll) = [1]> then
repeat until <(y position) > [179]>
change y by (Note-Speed)
end
else
repeat until <(y position) < [-179]>
change y by ((Note-Speed) * (-1))
end
end
delete this clone

The problem is that when lag happens, the repeat until loops slow down, but the music keeps playing at normal speed. How can I make the notes stay perfectly synchronized with the song even during performance drops? 🤔

Any rhythm game developers here who’ve solved this before? I really need help! 🙏

TS

TimingSync_Expert

Replied 2 hours later • ⭐ Best Answer

@RhythmGame_Creator This is a classic rhythm game synchronization problem! The issue is you’re using frame-based movement instead of time-based positioning. Let me show you the professional solution! 🎵

🎯 Understanding the Problem

Your current system moves notes by a fixed amount each frame, but when lag occurs:

flowchart TD A[🎵 Music Plays] --> B[60 FPS Normal] A --> C[30 FPS Lag] B --> D[Notes Move 60x per second] C --> E[Notes Move 30x per second] D --> F[✅ Perfect Sync] E --> G[❌ Notes Fall Behind] G --> H[💔 Game Becomes Unplayable] I[🔧 Solution: Time-Based Movement] --> J[Calculate Position from Timer] J --> K[✅ Always Synchronized] style A fill:#e1f5fe style F fill:#e8f5e8 style G fill:#ffebee style H fill:#ffebee style K fill:#e8f5e8

🔧 Solution 1: Time-Based Note Positioning

Instead of moving notes each frame, calculate their position based on elapsed time:

    // Setup timing system
when I receive [Start-Chart v]
set [Started at v] to (timer)
set [Chart BPM v] to [120] // Your song's BPM
set [Note Travel Time v] to [2] // Seconds for note to travel
forever
set [Current Time v] to ((timer) - (Started at))
end

🎵 Solution 2: Improved Note Movement

Replace your frame-based movement with time-based positioning:

    // In Note sprite
when I start as a clone
show
set [Note Start Time v] to (Current Time)
set [Note Lane v] to (Lane) // Which arrow lane

// Set costume based on note type
if <(Left-Hold-Note) = [1]> then
switch costume to [Hold]
else
switch costume to (join (Note-Skin) [_])
end

// Position based on lane
set x to ((Note Lane) * [100]) // Adjust spacing

forever
// Calculate time-based position
set [Time Elapsed v] to ((Current Time) - (Note Start Time))
set [Progress v] to ((Time Elapsed) / (Note Travel Time))

if <(Up-Scroll) = [1]> then
set y to ((-180) + ((Progress) * [360]))
else
set y to ((180) - ((Progress) * [360]))
end

// Delete when off screen
if <(Progress) > [1.1]> then
delete this clone
end
end

⚡ Solution 3: Advanced Timer System

Here’s the robust timing system that handles lag gracefully:

    // Master timing controller
define Update Timer System
set [Raw Timer v] to ((timer) - (Started at))

// Smooth out timer jumps from lag
if <((Raw Timer) - (Last Timer)) > [0.1]> then
// Large jump detected (lag recovery)
set [Timer v] to ((Last Timer) + [0.033]) // Max 1 frame jump
else
set [Timer v] to (Raw Timer)
end

set [Last Timer v] to (Timer)

// Update delay timer if needed
if <(Delay-Timer-Go?) = [1]> then
change [Delay-Timer v] by (1)
end

🎮 Solution 4: Beat-Synchronized Note Spawning

Spawn notes based on musical timing, not frame timing:

    // Note spawning system
define Spawn Notes for Beat (beat)
set [Beat Time v] to ((beat) / ((Chart BPM) / [60]))
set [Spawn Time v] to ((Beat Time) - (Note Travel Time))

if <(Current Time) > (Spawn Time)> then
if <(item (beat) of [Notes Spawned v]) = [0]> then
// Spawn note for this beat
set [Note Beat v] to (beat)
create clone of [Note v]
replace item (beat) of [Notes Spawned v] with [1]
end
end

🔧 Solution 5: Lag Compensation

Add intelligent lag detection and compensation:

    // Lag compensation system
define Handle Lag Compensation
set [Frame Time v] to ((timer) - (Last Frame Timer))
set [Last Frame Timer v] to (timer)

// Detect lag (frame took too long)
if <(Frame Time) > [0.05]> then // More than 50ms
set [Lag Detected v] to [1]
// Skip intermediate positions to catch up
change [Timer Offset v] by ((Frame Time) - [0.033])
else
set [Lag Detected v] to [0]
end

🎯 Solution 6: Perfect Hit Detection

Ensure hit detection works regardless of frame rate:

    // Hit detection based on time, not position
define Check Hit for Lane (lane)
set [Target Beat Time v] to (item (Current Beat) of [Beat Times v])
set [Hit Difference v] to (abs ((Current Time) - (Target Beat Time)))

if <(Hit Difference) < [0.1]> then // 100ms window
if <(Hit Difference) < [0.05]> then
broadcast [Perfect Hit v]
change [Score v] by [300]
else
broadcast [Good Hit v]
change [Score v] by [100]
end
else
broadcast [Miss v]
end

Key Benefits of This Approach:

  • 🎵 Perfect sync: Notes always match the music timing
  • ⚡ Lag resistant: Performance drops don’t affect synchronization
  • 🎯 Accurate hits: Hit detection based on time, not visual position
  • 📱 Cross-platform: Works consistently on different devices

The secret is to think in terms of musical time rather than visual frames. Your notes should always know exactly where they should be based on the song’s timeline! 🎵

RC

RhythmGame_Creator

Replied 4 hours later

@TimingSync_Expert This is absolutely incredible! 🤩

I implemented the time-based positioning system and the difference is night and day! Even when I deliberately cause lag by running other programs, the notes stay perfectly synchronized with the music.

The beat-synchronized spawning is genius - no more notes appearing at random times. My rhythm game finally feels professional! Thank you so much! 🎵✨

RD

RhythmDev_Pro

Replied 1 day later

Excellent solution! 🎮 Here are some additional pro tips for rhythm games:

  • 🎵 Audio latency: Add an audio offset setting for different devices
  • 📊 Performance monitoring: Track frame times to detect lag patterns
  • 🎯 Hit windows: Make hit timing windows slightly larger on lower-end devices
  • 💾 Preloading: Load all audio and sprites before starting the chart

Time-based systems are the foundation of all professional rhythm games! 🎵

VB

Vibelf_Community

Pinned Message • Moderator

🎵 Master Rhythm Game Development!

Amazing discussion on timing synchronization! For developers ready to create professional rhythm games, we can help you master:

  • 🎯 Advanced timing systems and beat detection
  • ⚡ Performance optimization for smooth gameplay
  • 🎮 Professional game feel and audio synchronization
  • 🔧 Cross-platform compatibility and testing

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