What it is and how it works
When the same sound arrives from two directions with a small delay, the ear perceives it as a single sound coming from the direction of the one that arrived first: this is the precedence effect (studied by Helmut Haas and others). Approximate values:
- Below about 1–2 ms: "summing" localization (the image moves between the two speakers).
- From about 2 ms up to 30–40 ms (for complex music and speech; up to about 50 ms depending on the signal): the two sounds fuse and the direction is that of the first. Haas observed that the delayed sound can be even up to about 10 dB louder without shifting the localization, for delays of about 10–30 ms.
- Beyond about 50 ms (speech and impulsive sounds) or 100 ms (music): a distinct echo is heard.
In production it is used like this: take a mono sound, send it to one channel as is and to the other delayed by 5–30 ms. The image becomes wide and "enveloping" while remaining a single sound. It is a cheap and very effective pseudo-stereo.
The problem: mono
When you sum the two channels (mono), the sound and its delayed copy create a comb filter: regular notches in the spectrum (the first notch is at 1/(2×delay): with 10 ms at 50 Hz, then 150, 250, 350 Hz…). The sound becomes "phasey", thin or metallic in mono. For this reason the Haas effect must be used judiciously and always checked in mono.
Parameters one by one
- Delay time: 5–15 ms = discreet width, more risk of an obvious comb filter in the mids; 15–30 ms = wider and "doubled"; 30–40 ms = starts to sound like doubling/slap.
- Delayed side: the sound seems to come from the non-delayed side; to balance the image, lower the leading side by 1–3 dB or raise the delayed one.
- Level of the delayed side: equal or slightly lower (−1/−3 dB).
- Different EQ on the two sides: one side slightly darker or with a different HP reduces the comb filter in mono and makes the effect more natural.
- Modulation (optional): a slightly varying delay makes the copy less "static" (toward a chorus).
- HP on the delayed side: 150–300 Hz, so the lows stay mono.
How to do it in FL Studio
- Fruity Stereo Shaper: the Delay control delays the right channel (turned right) or the left (turned left) by up to 500 ms to create pseudo-stereo on mono signals; the presets suggest 20–40 ms. The Phase control (all-pass filter 10 Hz–22 kHz) can decorrelate further.
- Fruity Delay 3: Mono model with Offset (delays one channel), Dry 100%, low Wet, feedback 0; or two instances.
- Double track: duplicate the channel, pan 100% L and 100% R, shift one of the two by 10–20 ms in the Playlist (or with the channel's time offset control), add slightly different EQs.
- Third-party: Waves Doubler, Soundtoys MicroShift (micro-pitch + delay, more mono-compatible), Polyverse Wider (compatible widening), iZotope Ozone Imager (Stereoize mode).
When to use it and on what
- Mono guitars (rhythm, arpeggios) when you don't have two takes.
- Mono synths (plucks, arpeggios, secondary leads) for width.
- Backing vocals and ad-libs (not the lead).
- Percussion (shaker, tambourine) for a wider air.
- Reverbs and delays (different pre-delay L/R).
- Mono pads.
Not on kick, bass, 808, lead vocal, snare: they must stay centered and mono-compatible.
Starting settings
| Source | Delay | Delayed side | HP on delayed side | Notes |
|---|---|---|---|---|
| Mono rhythm guitar | 12–20 ms | −1 dB | 150 Hz | slightly different EQ per side |
| Pluck/arpeggio | 8–15 ms | 0 dB | 200 Hz | check mono |
| Backing vocals | 15–25 ms | −2 dB | 200 Hz | or micro-pitch |
| Shaker | 10–20 ms | 0 dB | 400 Hz | — |
| Mono pad | 20–30 ms | 0 dB | 200 Hz | light modulation |
By genre
- Pop and EDM: Haas or micro-pitch on plucks, guitars and choirs; never on the lead.
- Rock: real double takes are better; Haas for single parts.
- Hip hop: ad-libs and samples widened.
- Lo-fi: guitars and piano discreetly widened.
Common mistakes
- Haas on elements with bass: comb filter in the low end and an unstable image.
- Delays of 1–5 ms: comb filter in the mids very audible in mono without real width.
- Unbalanced image (the sound "pulls" to one side): compensate with level or pan.
- Using it on many elements: the mix becomes "diffuse" and loses its focal point.
How to hear it
- Switch to mono: if the instrument becomes thin, metallic or loses volume, reduce the delay, lower the delayed side or use different EQs.
- Move the delay from 5 to 40 ms: hear the shift from "width" to "double" to "echo".
Starting settings
| Parameter | Value | Why |
|---|---|---|
| Delay | 5–30 ms (below the echo threshold) | Fusion and width. |
| Delayed side level | 0/−3 dB | Balanced image. |
| HP on delayed side | 150–300 Hz | Mono lows. |
| Different EQ per side | ±1–2 dB on different bands | Less comb filter in mono. |
| Fruity Stereo Shaper Delay | 10–30 ms (preset 20–40 ms) | Stock pseudo-stereo. |
Frequencies to watch
| Range | What to do |
|---|---|
| Below 150–300 Hz | HP on the delayed side: mono lows, no comb filter in the low end. |
| Comb notches: 1/(2×delay) and odd multiples | With 10 ms the first notch in mono is at 50 Hz, then 150, 250 Hz…; with 20 ms at 25, 75, 125 Hz…: check in mono. |
Example chain
| Step | Tool | Settings | Why |
|---|---|---|---|
| Processed mono source | EQ and compression | — | Clean signal. |
| Haas / pseudo-stereo | Fruity Stereo Shaper (Delay) / Fruity Delay 3 (Mono + Offset) / double track / MicroShift | 10–25 ms | Width. |
| EQ per side or on the delayed side | Fruity Parametric EQ 2 | HP 200 Hz, small differences | Mono compatibility. |
| Verification | Spreader (phase meters) / Wave Candy vectorscope | Correlation | Objective control. |
How to check the result
- Correlation of the track above 0 (better +0.3/+0.7).
- In mono the track loses no more than 2–3 dB and doesn't sound metallic.
- L/R balance: the sound shouldn't seem shifted to one side (L/R meters within 1 dB).