Any sound or music that exists within the film's world and can be heard by the characters — radio, ringing phones, footsteps. Contrast with non-diegetic sound like score, which only the audience hears.
Technical Foundations
Diegetic sound (from the Greek "diegesis," meaning "narrative") is any sound that originates from the film's world and can be perceived by the characters. In contrast to non-diegetic sound (such as film score), which only the audience hears, diegetic sound is part of the physical reality of the scene.
What is diegetic sound?
Classic examples:
- Dialogue between actors
- Music from a radio (character can hear it)
- Telephone ringing
- Car engine sound when car is shown
- Footsteps when actor walks across floor
- Doorbell
- Background noise (traffic, people talking) in the scene's environment
- Music that character plays (guitar, piano)
Test rule: If the character in the film can see or react to the source, the sound is diegetic.
Non-diegetic sound for contrast
Non-diegetic sound is sound that the characters do not hear:
- Film score (orchestral music for emotional effect)
- Voice-over narration (character speaks to audience, not to other characters)
- Ambient music (sound design element for audience emotion)
- Sound effects that dramatically support the scene (thunder for fear, for example)
Example scene with diegetic and non-diegetic sound
Scenario: Character sits alone in living room, grieving
Diegetic sound:
- Character breathing (diegetic – the character is breathing)
- Clock ticking on wall (diegetic – is in the room)
- Car driving by outside (diegetic – outside in the world)
- Character could turn on radio (diegetic)
Non-diegetic sound:
- Film music score (string music) plays over scene (non-diegetic – character does not hear this)
- Voice-over narration of the character (non-diegetic – inner thoughts, not dialogue)
Sound mixer approach:
- Diegetic sound: room-based, with reverb and spatial positioning (simulates 3D room acoustics)
- Non-diegetic sound: stereo-based, no room reverb (universal "over-the-scene" music)
Technical treatment of diegetic sound
1. Room sound characteristics
Diegetic sound must replicate the acoustic properties of the room:
| Room type | Characteristics | Audio treatment |
|---|---|---|
| Small room | Little reverb, tight reflections | Short early reflection (10-20ms), minimal reverb |
| Large hall | Much reverb, long reflections | Longer reverb (2-5 seconds), broad frequency spectrum |
| Outdoors (open air) | No reflections, long distance | No reverb, distance attenuation (higher frequencies quieter) |
| Car interior | Small room, hard surfaces | Short reverb, very "dry" and close |
| Bathroom | Tile reflections, high-frequency boost | Bright, "brilliant" reverb, +3-6dB above 2kHz |
2. Spatial positioning
Diegetic sound is spatially positioned:
Example:
A scene in a living room:
- Radio plays music (left side of room)
- Car horn sounds outside (from window, right)
- Character speaks (center, loud)
In the stereo mix:
- Radio: Left (~-6 dB, 80% Left, 20% Right)
- Car horn: Right (~-8 dB, 20% Left, 80% Right)
- Character: Center (~0 dB, 50% Left, 50% Right)
This creates a 3D spatial experience – the audience can "localize" where the sounds are in the room.
3. Distance simulation
Diegetic sound becomes quieter the farther it is from the camera:
Inverse square law (fundamental acoustic principle):
If a sound source is twice as far away, the volume drops by approximately 6 dB.
Practical example:
- Character speaks from close proximity: -6 dBFS (very loud)
- Character speaks 3 meters away (in another room corner): -12 dBFS (half as loud)
- Character speaks 10 meters away (outside): -18 dBFS (very quiet, nearly inaudible)
This is consistently applied to diegetic sound.
4. Frequency filtering at distance
The farther a sound source is, the more high frequencies are absorbed (by air and material):
Near field (< 2 meters):
- Full frequency response (20 Hz - 20 kHz)
Mid distance (2-10 meters):
- Reduced highs (-6 dB above 5 kHz)
- Full bass still present
Far field (> 10 meters):
- Heavily reduced highs (-12 dB above 5 kHz)
- Mids also reduced (-3 dB above 1 kHz)
- Dominant bass
Audio technique: A low-pass filter (e.g., cutoff at 4-5 kHz) acoustically simulates distance.
5. Diegetic sound through obstacles
When diegetic sound comes through walls, doors, or other objects:
Example: dialogue through closed door
- Original dialogue (close): dialogue is clear, brilliant
- Through wooden door: dialogue is muffled, high frequencies reduced
- Through thick concrete wall: dialogue barely intelligible, only bass rumbles
Audio technique:
- Increasingly aggressive low-pass filtering
- Level reduced (absorption through material)
- Reverb diminished (wall reflects less)
Practical applications of diegetic sound
1. Radio music in scene
Setup:
A character sits in a car and listens to the radio.
Diegetic treatment:
- Radio music has limited frequency band (simulates cheap radio speaker)
- Minimal bass (below 60 Hz attenuated)
- Heavily reduced highs (above 12 kHz attenuated)
- Focus on midrange (250 Hz - 4 kHz)
- Level can change when character adjusts volume (fader moves)
- Audio can sound "distorted" if character turns it up too loud (simulates speaker clipping)
Sound mixer approach:
- Music is filtered with a bandpass EQ (only midrange frequencies pass through)
- Optional: add slight distortion/compression (sounds cheap and "real")
- Spatial: music comes from car center (stereo, but limited)
2. Telephone conversation
Setup:
Character is on a phone call with someone.
Diegetic treatment:
- Other person's voice is treated through telephone filter:
- Heavily reduced highs (above 3 kHz very quiet)
- Mono instead of stereo (telephone = mono)
- Slight distortion/compression (telephone codec effect)
- Slight delay or pitch-shift (simulates telephone processing)
- Character's voice is normal (he/she speaks in room, not through phone)
Sound mixer approach:
- Other person's voice treated with specialized telephone EQ
- Optional: vintage telephone emulation plugin (e.g., Waves StudioEQ with telephone preset)
3. Music that character plays
Setup:
Character plays guitar or piano in scene.
Diegetic treatment:
- The music is live recorded or very naturally sounding samples
- Must synchronize with actor's movement (foley synchronization)
- Acoustic properties of instrument must be realistic
- Acoustic guitar: wood resonances, string vibrations
- Piano: hammer sound, string vibrations, pedal noises
Sound mixer approach:
- Instrument recording with correct microphone placement (e.g., 30cm from soundhole)
- Minimal EQ (let it sound natural)
- Reverb/reverb according to room acoustics (not aggressive)
4. Ambient sounds (traffic, people, nature)
Setup:
Scene outdoors in front of busy street.
Diegetic treatment:
- Traffic sounds are continuously audible (not constant)
- Distant voices/people are muffled and unclear
- Nature sounds (birds, wind) have characteristic properties
Sound mixer approach:
- Multiple ambience layers:
- Distant traffic (-20 dB, low-pass filtered)
- Near birds (-15 dB, high-frequency)
- Wind (-10 dB, context-dependent)
- Dynamic variation (not static) – real environment is never constant
Common mistakes with diegetic sound
| Mistake | Symptom | Cause | Fix |
|---|---|---|---|
| Too much room reverb on diegetic sound | Sounds "distorted" or "unnatural" | Wrong reverb settings | More subtle reverb, specific room emulation |
| No distance simulation | Diegetic sound sounds closer than visually | No low-pass filter or level adjustment | Apply distance EQ |
| Wrong level balance | Character dialogue much louder than ambience | Dialogue peak is -3 dBFS, radio music is -25 dBFS | Better level planning, compression for dynamics control |
| Incorrect spatial positioning | Diegetic sound sounds "mono" or wrongly placed | No stereo positioning | Pan (left/right) based on visual location |
| Too artificial radio filter | Radio doesn't sound authentic | Too aggressive low-pass or distortion | More subtle filtering, check spectral balance |
Summary
Diegetic sound is the "reality" of the film – the world the characters inhabit. Good diegetic sound treatment makes the difference between a film that feels "real" and one that feels "artificial."
Best practice:
- Spatial characteristics: reverb and reflections according to room type
- Distance simulation: level and EQ based on visual distance
- Frequency filtering: reduce high frequencies at distance
- Continuous nature: ambient sounds are dynamic, not static
- Subtlety: diegetic sound should often be inaudibly subtle to be believable
A film with realistic, well-treated diegetic sound feels much "more real" and immersive than a film where everything is "score and voice-over."