Fix: Unity Cinemachine Impulse Listener Not Shaking

Here is how to fix Cinemachine Impulse Listener not shaking when the source generates a signal. You set up an Impulse Source on an explosion prefab, attach a CinemachineImpulseListener to your virtual camera, and call GenerateImpulse. Nothing happens. The console shows no errors, the source thinks it fired, but the camera holds perfectly still. Almost always, the channel mask, the signal asset, or the listener gain is the culprit.

The Symptom

An CinemachineImpulseSource calls GenerateImpulse on a hit event. The callback runs, no exceptions are thrown, the impulse profiler shows a signal was generated — but the active virtual camera does not move. Other camera shake systems (like Cinemachine Basic Multi Channel Perlin) work correctly, so the camera setup itself is fine.

What Causes This

Channel mismatch. Each impulse source broadcasts on a channel; each listener subscribes to a channel mask. If your source is on channel 4 but your listener listens only to channel 1, the signal is filtered out. Channel masks are bitwise, so subscribing to multiple channels requires combining flags.

No Raw Signal asset. The Impulse Source has a Raw Signal field that points to an ImpulseSignal asset (a curve over time). If this is empty, the source generates a zero-amplitude signal. Cinemachine ships with several presets like 6D Shake and Recoil.

Listener Gain is zero. The listener has a Gain multiplier applied to incoming signals. If it is set to 0, every signal is multiplied to nothing.

Source out of range. Impulse signals decay with distance. If the source is far from the camera and the source’s Impact Radius and Dissipation Distance are small, the camera receives an attenuated signal that is too weak to see.

The Fix

Step 1: Verify channel match. Open the Impulse Source and the Impulse Listener inspectors side by side. The source has a Channel dropdown. The listener has a Channel Mask. Both should include at least one common channel.

Step 2: Assign a Raw Signal. On the Impulse Source, drag a signal asset into the Raw Signal field. Use the Cinemachine’s built-in 6D Shake as a starting point.

Step 3: Generate the impulse with explicit force.

using UnityEngine;
using Unity.Cinemachine;

[RequireComponent(typeof(CinemachineImpulseSource))]
public class ExplosionShake : MonoBehaviour
{
    private CinemachineImpulseSource source;

    void Awake() { source = GetComponent<CinemachineImpulseSource>(); }

    public void Boom(float magnitude = 1f)
    {
        // Pass a velocity vector for directional shake
        Vector3 velocity = Random.insideUnitSphere * magnitude;
        source.GenerateImpulseWithVelocity(velocity);
    }
}

Step 4: Confirm listener Gain. On the CinemachineImpulseListener, set Gain to 1.0 for a baseline. Also confirm Use 2D Distance matches your project (enable for top-down 2D games so depth differences do not attenuate the signal).

Step 5: Tune dissipation.

// In the source inspector or via code:
source.ImpulseDefinition.ImpactRadius = 5f;
source.ImpulseDefinition.DissipationDistance = 100f;
source.ImpulseDefinition.DissipationRate = 0.25f;

A small radius means the camera must be very close to feel the full force. A large dissipation distance means the signal travels far before decaying. For first-person games where the source and camera are usually nearby, set Impact Radius to roughly the player’s effective range.

Verifying the Pipeline

Drop a quick debug log on each end:

// Subscribe to listener events
void OnEnable()
{
    listener.RegisterCallback((Vector3 pos, Quaternion rot) => {
        if (pos.sqrMagnitude > 0.0001f) Debug.Log($"Got impulse: {pos}");
    });
}

If you see logs but no visible motion, the signal is too small — raise gain. If you see no logs at all, the channel or signal asset is wrong.

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Unity Engine, the underlying behavior is shaped by how the engine layers its abstractions - the public API you call, the runtime systems that respond, and the platform-specific implementations underneath. A bug at any layer can produce symptoms that look like they originate at a different layer. Triaging effectively means recognizing which layer the symptom belongs to, even when the gameplay code is what's visible.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

This bug class disproportionately affects late-stage development. The work to surface it is interactive testing in realistic conditions, which only really happens after the gameplay is in place and assets are populated. Catching it early requires deliberate testing of conditions that look unimportant.

At the engine level, the behavior comes from a deliberate design decision in Unity. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

After applying the fix, the verification step has three parts: confirm the original repro is resolved, confirm no obvious regressions in adjacent functionality, and (for shipping titles) deploy to a small player cohort first and watch the crash and report rates. Each step catches something the others miss.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

Related bug classes often share the same root cause. If you find yourself fixing this issue, look for cousins: similar symptoms in adjacent systems, the same data flow but a different value, or the same fix pattern in another module. The catalog of 'we've seen this before' becomes valuable institutional knowledge.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

For shipping titles with a long support window, watch for this issue resurfacing after dependency updates. Engine upgrades, driver updates, OS releases - each one can resurface a bug class you thought you'd fixed because the underlying behavior changed slightly. Regression tests catch the obvious ones; player reports catch the rest.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

If this issue manifests under high load (many actors, many particles, many network connections), profile the post-fix code path with realistic counts. The original cost was a bug; the new cost is real work, and real work has a budget.

Diagnostic approach

Diagnosing this class of bug benefits from a structured approach: confirm the symptom, isolate the variables, hypothesize the cause, and verify the hypothesis before writing fix code. Skipping the isolation step is the most common mistake; without it, fixes often address symptoms while the underlying cause continues to produce other variations.

For Unity-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

The tooling around this bug class matters as much as the fix itself. Good logging, accessible profilers, and clear error messages turn 30-minute investigations into 5-minute ones. If your project doesn't have visibility into this code path, the first fix should add the visibility - the second fix uses it.

Within Unity, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Platform-specific edge cases are worth enumerating explicitly. iOS handles backgrounding differently than Android; Windows handles focus changes differently than macOS. A fix that works on the development platform may not work on every target. Test on each shipping platform deliberately.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

Document the fix and its rationale in the commit message or attached engineering doc. Future engineers will encounter related issues; the rationale tells them whether your fix is reusable or specific to the case at hand. Without rationale, the fix gets reverted or copied incorrectly.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Channels match, signal assigned, gain non-zero, source within dissipation range. Four checks, in order, every time.”

Related Issues

For other Cinemachine motion problems, see Cinemachine Camera Jitter and Cinemachine Camera Shaking.

Channels are silent when they mismatch. Check both ends.