Distance Perception in Mono

Distance perception in mono

Make a sound seem to approach, pass, and recede without stereo panning.

Identify the cues that suggest distance.
Use automation to coordinate those cues in your Mono Sound Walk.

Cues to distance

Level: a source usually gets quieter as it moves away.
Brightness: high-frequency loss can make it seem more distant.
Direct-to-reverberant balance: reflections become more prominent relative to direct sound in a room.

Level and distance

For a point source in a free field, doubling distance reduces sound pressure level by about 6 dB.

Distance	Example level
1 m	70 dB SPL
2 m	64 dB SPL
4 m	58 dB SPL
8 m	52 dB SPL

Predict the level at 16 m.

Distance calculator

Brightness and filtering

Air absorption can reduce high frequencies over distance.
A low-pass filter lets you imitate reduced brightness.
A duller sound can also suggest an obstacle or a different source.

Distance, loudness, and filtering

Open the interactive spatial audio demo

Distance only: enable distance/loudness. Move toward and away from the target. Which sounds closer?
Filtering only: disable distance/loudness and enable low-pass. Does a duller sound suggest distance or obstruction?
Both cues: enable distance/loudness and low-pass. Do the cues agree about how far away the sound seems?

Move with the arrow keys or WASD. Keep panning, ITD, and pulse rate off.

Click Start audio, then click the World area to use the movement keys.
For distance only, turn off low-pass, panning, ITD, and pulse rate. Enable distance/loudness. Move toward and away from the target and observe the distance and gain readouts.
Have students close their eyes while you choose two positions. Play at each position and ask which seems closer, then reveal the positions. Keep the computer’s playback volume fixed.
For filtering only, disable distance/loudness and enable low-pass. Watch the cutoff readout as you move vertically. Ask whether brightness alone changes apparent distance.
This demo maps filtering to vertical position. It is a designed spatial cue, not a calibrated simulation of air absorption over metres.
Ask students to describe the impression before explaining it. Reduced brightness can suggest distance or obstruction, depending on context.
Finally enable both distance/loudness and low-pass. Because they follow different position rules, the cues can reinforce or conflict with one another. Ask which cue students rely on when they disagree.
Source: Spatial Audio Accessibility Demo . Allow about four minutes.

Direct-to-reverberant ratio

DRR compares direct sound with the room’s reflected sound.

Higher DRR often suggests a closer source.
Lower DRR often suggests a more distant source.
Judge the balance in the context of the room.

Larsen et al.: Discrimination of direct-to-reverberant ratio

Which violin sounds closer?

Compare A1 with B1, then A2 with B2. Vote: A closer, B closer, or no difference. What sound cue led you to that choice?

A	B
A1	B1
A2	B2

Source: akuTEK, Intimacy—monaural

Play one ten-second example at a time, keeping the playback volume fixed. Collect votes before explaining the processing.
These are judgments of perceived closeness. The files do not represent known near, mid, and far distances, so do not ask for estimates in metres or score a subjective response as wrong.
First compare A1 with B1, then A2 with B2. In each pair, B has a 6 dB higher direct-to-reverberant ratio than A. The reverberant tail has the same content and level across all four files. A stronger direct component is a cue that can suggest a closer source. Ask whether students heard that effect.
Then compare A1 with A2, or B1 with B2. The direct-to-reverberant ratio stays the same within each letter pair. Example 1 has a 33 ms gap before the reverb begins; example 2 has no gap. Ask whether this changes perceived closeness or just the character of the room.
The clips isolate direct-to-reverberant balance and reflection timing. They are not a demonstration of high-frequency roll-off with distance.
Source and processing details: akuTEK, Intimacy—monaural . Audio streams from akuTEK and requires an internet connection.

Convolution reverb for believable rooms

An impulse response captures how a space or reverb system responds to a brief input.

Load an IR into ReaVerb to establish the environment.
Keep that room consistent while changing the direct/reverb balance.
Use level and filtering to support the source’s movement.

OpenAIR: measured spaces · Samplicity M7: reverb-unit IRs

Editing automation in REAPER

Make one mono sound approach, pass, and recede.

Select the track and press V to show its volume envelope.
Draw a quiet–loud–quiet fade. Ctrl/Cmd-drag in the lane draws freehand.
Alt/Option-drag a segment to reshape the transition. Listen for believable movement.
Adjust an FX control, then run FX: Show/hide track envelope for last touched FX parameter to automate it.

Resources:

Demonstrate editing an envelope before the next slide’s live fader recording. Keep the source mono and panning centered.
Start quietly, rise to a peak at the closest point, then fall away. Let students compare a steady ramp with a curved transition and describe the implied motion.
Curve names describe how parameter values change over time. A shape alone does not establish approach or departure; the direction of the change and the parameter matter.
For precise point editing, Ctrl/Cmd-double-click a point. Alt/Option-click removes a point. Mouse modifiers can differ in customized REAPER setups.
For an FX envelope, adjust the desired control first, open the Actions list with ?, and search for the action shown on the slide. The article author’s L shortcut is a personal assignment, not a default.
The combined practice will extend this volume envelope to the filter and room balance introduced earlier.
Optional extension: Alt/Option-drag along the bottom of an envelope lane to create an automation item. Reuse a movement pattern by copying or stretching it.
Source: Reapertips: 10+ Automation Shortcuts in REAPER .

Recording automation live

Touch: write while moving a control, then return to the existing envelope.
Latch: keep writing the last value after releasing the control, until playback stops.
Write: overwrite armed envelopes throughout playback.

Practice: one sound moving through a room

Use the same mono clip and room throughout.

A volunteer draws or records its approach and departure.
Another adjusts filter cutoff to support the movement.
A third adjusts the direct/reverb balance.

Listen without the screen. Where does the sound seem closest?

Echoes and reflection timing

A delay can represent a distinct reflection from a surface.
Delay time describes the extra travel path of that reflection.
Feedback adds repeats; their level and brightness affect the impression.

Optional: add one quiet, filtered echo to the moving sound.

Doppler and moving sources

Relative motion can shift the pitch we hear.

Approaching sources can sound higher in pitch.
Receding sources can sound lower in pitch.
Use the effect when the source’s speed makes it relevant.

Optional: compare the pass-by with and without a pitch shift.