Who's There? Exploring the Use of Knocking Sound Effects in Cinema

Knocking sound effects in classic films

The pace and pattern of a knocking sound effect is as important as the timbre of the sound itself. A fast and furious effect implies that the visitor is rushing to connect with whoever’s inside. A shy and slow tap might suggest a nervous visitor who fears the moment of contact. In some cases, the rhythm of a knock acts as a secret code. Let’s explore further in the sections below.

The Shining, The Matrix – Door knocking sound effects

Stanley Kubrick’s classic movie The Shining features an iconic and intense knock-knock moment from horror film history. Jack Nicholson’s arhythmic knocking is paired with maniacal facial expressions to build tension and add a layer of fear to the sequence. Like the big bad wolf, his innocent knock is followed by a burst of violence as he chops through the door with an axe.

An equally important moment takes place near the beginning of The Matrix, when Keanu Reeves’ character Neo receives a series of cryptic messages from an unknown sender on his computer. After a few exchanges, they send the words Knock, Knock, Neo, and he’s alarmed to hear two loud knocks on his apartment door. The startling timbre of their aggressive knocking helps the audience connect with Neo’s ominous feeling of being watched.

Insidious 3, Who Framed Roger Rabbit – Knocking on a wall

The timbre of knocking sounds on a wall are usually more hollow. They could carry an intimate connotation when the knock comes from a neighbor rather than an outside visitor, like in the scene below from The Summer I Turned Pretty.

A series of soft knocks are exchanged between young lovers in neighboring bedrooms. They can’t share the same room, but the sound is a reassuring sign that they are aware of each other and not too far away.

An almost identical scene plays out in the supernatural thriller Insidious: Chapter 3, when the main character Quinn knocks on her bedroom wall to connect with her neighbor, Hector. She hears a response knock and swoons, taking out her cell phone to begin texting him. But she quickly learns that Hector is not at home. It comes out that the knocking sound came from an evil spirit.

These two examples demonstrate how the same sound effect can have opposite meanings.

Knocking on a wall can also represent the pursuit of someone in hiding. This scene from Who Framed Roger Rabbit show a villain named Judge Doom pursuing the main character. Each knock is followed by a period of pause and listening, to see if someone behind the wall reacts. Judge Doom knocks with a metal-tipped cane, changing the timbre of the sound from the usual bare knuckle knocking sound to a harder and higher pitched tone.

A Beautiful Mind, Marshall, Bobby Fischer – Knocking on a table

Knocking on a table carries a completely different set of meanings from doors and walls. It’s often a sign of authority and endings. The intensity of the knocking sound effect often conveys the intention behind the person making the statement.

An obvious example of this is the knocking of a judge’s gavel against the podium’s sound block. In the scene above, a defendant is declared not guilty and an immense feeling of relief washes over the audience. But the same fateful knock can also carry a guilty sentence and have the opposite effect.

Like a gavel, games of chess are finalized when one player knocks over their king in a sign of resignation. The light timbre of this knocking sound effect can carry immense weight, as in the climactic scene above from Searching for Bobby Fischer.

In this scene from A Beautiful Mind, the professor’s resignation is met by a moment of warm and supportive knocking sound effects, as each of his colleagues places their pen down on the table in a show of support. As each pen drops, its gentle knock against the wooden table reiterates their humble and singular appreciation for him.

Wolf of Wallstreet, Three Stooges – Knocking against body parts

Characters have known to occasionally knock on body parts. The pairing of a hollow knocking sound with characters being tapped on the head might be used for comedic effect, to imply that person is being absent minded.

Knocking on human heads was a common trope in the Three Stooges. Notice that in some cases, the knocking sound effect resembles a popping bubble. The use of unlikely sounds adds to the absurdity and humor of these scenes.

The scene above from Wolf on Wallstreet shows two men in business suits knocking repeatedly on their chest in a tongue-in-cheek moment of solidarity. Similar gestures are common in scenes where a warrior is asserting their strength and confidence.

Stranger Things, Harry Potter – Knocking in coded rhythms

A tap-t-t-tap-tap pattern on someone’s door is a classic way to let people know you’re a friendly visitor. But there are other examples in films where characters knock to convey secret messages. The scene below, from Stranger Things, features a character named Will tapping out Morse code to secretly communicate a phrase to his friends.

Playing on this theme, the movie Harry Potter and the Order of the Phoenix features this scene where three knocks of a wizard’s staff are required to open up the entrance to Grimmauld Place.

How to create and use knocking sound effects

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Transforming a simple knocking sound into an ominous pulse element can add tension and atmosphere to a thriller scene. Here’s a detailed guide on how to achieve this using transposition, playback speed manipulation, saturation, and reverb.

Step-by-Step Guide to Creating Ominous Knocking Sounds

1. Recording and Preparing the Knocking Sound

• High-Quality Recording:
  • Capture a clean, high-quality recording of a knocking sound. Use a condenser microphone to ensure the details and nuances are captured.
  • Record multiple takes to have a variety of options to choose from.

2. Transposing and Slowing Down Playback

• Transposition:
  • Import the knocking sound into your DAW.
  • Transpose the sound an octave down to lower its pitch, creating a deeper, more menacing tone.
  • Plugin Recommendations: Ableton Live’s Transpose function, Logic Pro’s Pitch Shifter, or Waves SoundShifter.
• Slowing Down Playback:
  • Reduce the playback speed to stretch the sound, adding weight and an eerie, drawn-out quality.
  • Techniques:
    • In Ableton Live, use the Warp function and adjust the tempo.
    • In Logic Pro, use Flex Time and set the algorithm to Flex and Slow.
    • Ensure the time-stretching algorithm preserves the quality of the sound.

3. Applying Saturation for Greater Definition and Power

• Saturation Plugins:
  • Plugin Recommendations: FabFilter Saturn, Soundtoys Decapitator, or Waves J37 Tape.
  • Apply saturation to the transposed and slowed-down knocking sound to enhance its harmonics and add a gritty, powerful edge.
  • Adjust the drive and mix parameters to blend the saturated sound with the original, ensuring it adds definition without overwhelming the natural tone.

4. Adding Reverb for Natural Decay and Spatial Effect

• Reverb Plugins:
  • Plugin Recommendations: Valhalla Room, Waves H-Reverb, or Altiverb.
  • Apply a large, ambient reverb to the knocking sound to create a sense of space and allow the sound to decay naturally.
  • Adjust the wet/dry mix to ensure the reverb complements the sound without drowning it out.
  • Set the decay time and pre-delay to create a haunting, lingering effect that fills the air.

5. Fine-Tuning and Additional Effects

• EQ and Filtering:
  • Use EQ to shape the final sound, removing any unwanted frequencies and enhancing the desired characteristics.
  • Apply a low-pass filter to remove any high-end noise introduced during processing.
  • Plugin Recommendations: FabFilter Pro-Q 3, Waves Q10, or Logic Pro’s Channel EQ.
• Compression:
  • Apply compression to control the dynamics and glue the sound together.
  • Use a slow attack and release to maintain the natural decay of the knocking sound.
  • Plugin Recommendations: Waves SSL G-Master Buss Compressor, Logic Pro’s Compressor, or FabFilter Pro-C 2.
• Automation:
  • Automate volume, reverb, and saturation parameters to create dynamic changes and add movement to the sound.

Tips for Effective Ominous Knocking Sound Design

• Experiment with Transposition: Different pitch levels can produce varying degrees of unease, so experiment with transposing by different intervals.
• Layering for Depth: Layer multiple transposed and slowed-down knocks for a richer, more complex sound.
• Use of Reverb: Choose reverb settings that match the atmosphere of the scene, whether it’s a large, empty space or a claustrophobic, echoing environment.
• Attention to Detail: Fine-tune each processing step to ensure a polished, professional result that enhances the tension and atmosphere of the scene.

By following these steps and tips, you can transform a simple knocking sound into a powerful, ominous pulse element that adds tension and atmosphere to thriller scenes. Experiment with different techniques and effects to develop your unique sound design style.

If you don’t have access to a foley studio, you can download the royalty-free knocking sounds we’ve provided in this article. Pick up a free copy of Audio Design Desk to make it even easier to select and place sounds on your video timeline.