What it is
A stereo imager changes the perceived width of a stereo signal by altering the ratio between Mid (center) and Side (sides). Raising the Side widens, lowering it narrows; at 0% Side the signal is mono. Many imagers are multiband: they let you keep the bass narrow and widen the mids and highs. True widening techniques, on the other hand, create differences between the two channels where there were none before.
Widening techniques (from the most to the least compatible)
- Arrangement and recording: two different takes (double-tracked guitar, doubled backing vocal) panned L/R. This is the most natural widening and is perfectly mono-compatible, because in mono the two takes add up like a double, without cancellations.
- Panning different mono instruments to different positions (hi-hat 30% R, shaker 40% L, guitars 80–100%).
- Native stereo sounds: synths with detuned unison, stereo pads, stereo miking (XY, ORTF, AB).
- Modulation: chorus, ensemble, dimension (see “Chorus, flanger, phaser and ensemble”).
- Mid/Side: raising the Side or the Side EQ (air on the sides).
- Micro-pitch / micro-shift: a copy transposed by ±5–15 cents and delayed by 10–25 ms per side (Eventide H910/MicroPitch style). Wide, but reduces intelligibility if too high.
- Haas: a 5–30 ms delay on one side (see “Haas effect”). Very wide, the least compatible in mono (comb filter).
- Decorrelation and “psychoacoustic” wideners: different all-pass filters on the two channels. High width, with a risk of an “out of head” sound and cancellations.
Multiband imager: starting values
| Band | Width (100% = unchanged) | Reason |
|---|---|---|
| Below 120 Hz | 0% (mono) | Stable low end in clubs, mono and vinyl |
| 120–500 Hz | 80–100% | Warmth without mud on the sides |
| 500 Hz–4 kHz | 100–115% | Body and width of harmonic instruments |
| Above 4 kHz | 110–130% | Air and space |
In mastering do not exceed +10/+15% on the high bands: a narrow mix is fixed in the mix, not with the imager.
Use by source
- Pads and accompaniment synths: wide (correlation +0.2/+0.5), HP on the Side at 150–200 Hz.
- Lead and vocal: centered and narrow; width comes from the sends (stereo reverb, ping-pong delay) and from doubles.
- Backing vocals: panned doubles, imager +10/+20% on the high bands.
- Drums: stereo overheads and room; kick, snare and bass in the center.
- 808, sub, bass: mono below 120–150 Hz; any stereo saturation only above 300 Hz.
- FX and transitions: can be very wide, they are short and do not carry the song.
Tools
- FL Studio: Fruity Stereo Shaper (control of L/R, phase inversion, delay between channels), Fruity Stereo Enhancer (width, delay and phase), the mixer track's Stereo separation knob (left widens, right narrows). For multiband: Patcher with a crossover or external plugins.
- External: iZotope Ozone Imager (free, multiband and vectorscope), Polyverse Wider, Waves S1, Kilohearts Haas, Soundtoys MicroShift, Eventide MicroPitch.
Common mistakes
- Widening the master to 150%: in mono the vocal and the main instruments change volume and the mix turns hollow.
- Imager on tracks that contain bass: the low end loses power and on vinyl it causes groove problems.
- Widening everything: if everything is wide, nothing is. You need contrast between a narrow center and wide sides.
- Haas or decorrelation on the lead vocal: it loses the center and intelligibility in mono.
- Judging width on headphones: headphones exaggerate separation. Check on speakers and in mono.
Starting settings
| Parameter | Value | Why |
|---|---|---|
| Bass | Mono below 120–150 Hz | Power and compatibility. |
| Pads and synths | Correlation +0.2/+0.5 | Wide but compatible. |
| Imager in mastering | Maximum +10/+15% on the high bands | A narrow mix is fixed in the mix. |
| Micro-pitch | ±5–15 cents, 10–25 ms, mix 15–30% | Width on supporting vocals and synths. |
| Haas | 5–30 ms on secondary elements only | Comb filter in mono. |
| Check | Average correlation above +0.2 | No loss in mono. |
Frequencies to watch
| Range | What to do |
|---|---|
| Below 120 Hz | Width 0% (mono): kick, bass, 808, sub. |
| 120–500 Hz | Natural width; avoid widening so as not to swell the mud on the sides. |
| 500 Hz–4 kHz | Body of harmonic instruments: moderate width. |
| Above 4 kHz | Air and space: +10/+30% on tracks, maximum +10/+15% in mastering. |
Example chain
| Step | Tool | Settings | Why |
|---|---|---|---|
| Source | Double takes, stereo synths | Natural width | The most compatible. |
| Panning | FL Studio mixer | Different positions | Separation of the instruments. |
| M/S EQ | Pro-Q / Ozone | Side HP 120–200 Hz | Bass in the center. |
| Imager | Ozone Imager / Fruity Stereo Enhancer | +10/+30% on the high bands | Air and space. |
| Measurement | Ozone Imager vectorscope / Wave Candy | Correlation and Lissajous | Mono compatibility check. |
How to check the result
- Side/Mid width in the Sub and Bass bands: −20 dB or less (mono).
- Side/Mid width in Presence and Air: between −8 and −2 dB for an open mix; near 0 dB or above, excessive width.
- Average mix correlation between +0.2 and +0.8; negative stretches only on short FX.
- Mono (sum) loudness no more than 1.5–2 LU below the stereo one; lead vocal with the same loudness in mono and stereo.
- L/R balance within ±0.5 dB.