Certain events in Left 4 Dead and Left 4 Dead 2 have associated audio cues. These take the form of sound queues that play when Special Infected spawn, or sounds that the Special Infected make while waiting to attack.
Special Infected[]
Note: Each Special Infected has a different number of notes in their audio cue. A strings cue indicates the Special Infected has spawned far away, and a piano cue means that it has spawned nearby.
| Number of notes: | 2 | 3 | 4 | 5 | 6 | 8 |
|---|---|---|---|---|---|---|
| Special Infected: | Smoker | Hunter | Spitter | Boomer | Charger | Jockey |
| Infected Name | Idle sound file | Audio Cue (Piano) | Audio Cue (Strings) | Notes |
|---|---|---|---|---|
| Boomer | A low vomiting and belching sound | C D# E F E(sus) | C D# E F E(sus) | The audio cue is played 2 octaves down. |
| Charger | Hoarse yells | G# G A# A G G# | G# G A# A G G# | The audio cue is played 2 octaves down. |
| Hunter | A low growling sound | D C C# | D C C# | The Hunter will only make an idle sound while he is crouched. The audio cue is played both 2 octaves up and 3 octaves up. |
| Jockey | Hoarse, manic laughter | C C C C C# C B C | C C C C C# C B C | The audio cue is played 1 octave down and 2 octaves down. |
| Smoker | A dry cough | F-G# E | F-G# E | The audio cue is played 2 octaves down. |
| Spitter | A wet cry or gargle | A A# G# A | A A# G# A | The audio cue is played 2 octaves up. |
Boss Infected[]
These infected do not have preset audio cues by the game, but they do have boss music and do make their own idle sounds.
| Infected Name | Idle sound file | Music | Notes |
|---|---|---|---|
| Tank | A deep nasal breathing or growling | A low mixture of bass, drums, and a capella mixture, with some light flute and piano | The idle sounds for a Tank can only be heard on Campaign mode, where the Tank is pre-spawned and waits for the Survivors. In other game modes, the Tank automatically targets the Survivors. |
| Witch | A keening wimper | A high mixture of a capella, drums, and some fast piano, with some string and wind instruments | None |