MIDI CC (Mod Wheel) Signal Loss in Logic Pro

Applicable Products

• Virtual Guitarist (all series)
• Usynth
• Virtual Bassist (all series)
• Beatmaker (all series)
• Symphonic Elements

Technical Issue Summary

Input from specific hardware controllers (commonly Mod Wheel/CC1, Expression/CC11) fails to reach the active Instrument Track. The signal is intercepted at the Physical Input stage by the Control Surface subsystem before reaching the Sequencer Input object in the Logic Environment.

System Architecture & Root Cause

1. The Interception Point

Logic Pro's MIDI signal flow differs from standard signal paths. The Controller Assignments database sits between the hardware driver and the Sequencer:

• Path: Hardware Driver → Controller Assignments (Interception) → Sequencer Input → Active Track

Any MIDI message defined in the Controller Assignments database is consumed at the interception point. It is not duplicated; it is routed exclusively to the assigned parameter (e.g., a specific plugin knob or fader).

2. Persistence Mechanism

Unlike project-specific mappings in other DAWs, Logic Pro Controller Assignments are stored in the global User Preferences, not the project file.

• Storage Location: ~/Library/Preferences/com.apple.logic.pro.cs
• Consequence: A mapping created for a specific plugin in Project A remains active globally. If you open Project B and try to use the Mod Wheel on a UJAM instrument, the system-level assignment steals the CC1 message to control the (potentially missing) parameter from Project A.

3. MIDI Hex Data Identification

In the diagnosis steps below, identifying the conflict requires recognizing specific MIDI Status Bytes in the Expert View.

• CC1 (Mod Wheel) Channel 1: Status: B0, Data 1: 01
• CC1 (Mod Wheel) Channel 2: Status: B1, Data 1: 01
• CC11 (Expression) Channel 1: Status: B0, Data 1: 0B

Diagnosis and Resolution (Expert View)

Step 1: Open Controller Assignments

1. Launch Logic Pro.
2. Execute Key Command: Command + K.
3. CRITICAL: Toggle the view from Easy View to Expert View (Button usually located at top-left or bottom-left depending on Logic version). Easy View filters out inactive assignments, hiding the root cause.

Step 2: Locate the "Zombie" Assignment

Navigate the columns in the Expert View window:

1. Zone (Left Column): Select (No Zone) or Global.
2. Control/Parameter (Center Column): Scan the list. You are looking for assignments that are not standard Mackie Control/HUI commands.
3. Input Message (Right/Bottom Panel):

• Select an assignment in the center list.
• Inspect the Value Change field.
• Identify the hex code B0 01 (or your specific controller's ID).

Step 3: Delete and Purge

1. Highlight the conflicting assignment (e.g., "Phase Plant: Mod Wheel").
2. Press Delete (Backspace).
3. Verification: Immediate functionality restoration. No restart required. The signal path Physical Input → Sequencer Input is re-established immediately upon deletion.

Technical Appendix: DAW Architecture Comparison

Logic Pro's handling of MIDI mapping is architecturally distinct from other industry standards. Understanding this distinction helps in diagnosing why "Learn" functions behave differently here.

External References

• Controller Assignments Expert View Parameters
• Logic Pro CS Preference File Structure
• Why won’t logic record the modulation wheel movements when setting automation for a track?
• Controller Assignment Problem in Logic Pro