Pan law is how much a mono sound is turned down on each side when it sits in the center, so it doesn’t sound louder there than panned hard. With the common −3 dB law the stereo loudness stays even across the pan, but fold the mix to mono and anything in the center comes out 3 dB louder than the same sound panned hard. That’s why hard-panned guitars and hats seem to fall back on a phone or a club’s mono system.

You balance the mix on headphones and it feels right: guitars wide, hats off to one side, vocal and 808 dead center. Then you hit the mono button, or play it on a phone, and the vocal and bass jump forward while the panned parts sink. Nothing is out of phase. The correlation meter looks fine. It’s still a different mix.

Most of that shift comes from a setting you probably never chose: the pan law.

What the pan knob is actually doing

A mono track panned to the center plays out of both speakers. Two speakers playing the same thing add up, so if the panner left both sides at full level, the sound would get louder every time you moved it toward the middle. A pan law turns both sides down at center to stop that. The question is by how much, and there are four common answers. This little script prints all four for a sound in the center, halfway left (L50) and hard left (L100):

#!/usr/bin/env python3
"""Pan law table: per-side gain and level change for a mono source, in stereo and folded to mono.
Levels are relative to the same source panned hard to one side (which every law leaves at unity)."""
import math, sys

def gains(law_db, pos):
    """pos -1 (hard L) .. 0 (center) .. +1 (hard R). Returns (L, R) linear gains."""
    t = (pos + 1) / 2                      # 0..1
    if law_db == 0:                        # balance-style: center is unity on both sides
        return min(1, 2 * (1 - t)), min(1, 2 * t)
    p = math.cos(t * math.pi / 2), math.sin(t * math.pi / 2)   # constant power, -3 dB at center
    lin = 1 - t, t                                              # linear, -6 dB at center
    if law_db == -3: return p
    if law_db == -6: return lin
    if law_db == -4.5: return tuple(math.sqrt(a * b) for a, b in zip(p, lin))
    raise SystemExit("laws: 0, -3, -4.5, -6")

db = lambda x: 20 * math.log10(x) if x > 0 else float("-inf")
laws = [float(a) if "." in a else int(a) for a in sys.argv[1:]] or [0, -3, -4.5, -6]
print(f"{'law':>6} {'pan':>6} {'L gain':>8} {'R gain':>8} {'stereo':>8} {'mono':>8}")
for law in laws:
    for pos, name in ((0, "C"), (-0.5, "L50"), (-1, "L100")):
        l, r = gains(law, pos)
        stereo = 10 * math.log10(l * l + r * r)    # acoustic power from two speakers
        mono = db(l + r)                           # both sides summed to one speaker
        print(f"{law:>5}dB {name:>6} {db(l):>7.1f}  {db(r):>7.1f}  {stereo:>+7.1f}  {mono:>+7.1f}")

$ python3 pan_law.py
   law    pan   L gain   R gain   stereo     mono
    0dB      C     0.0      0.0     +3.0     +6.0
    0dB    L50     0.0     -6.0     +1.0     +3.5
    0dB   L100     0.0     -inf     +0.0     +0.0
   -3dB      C    -3.0     -3.0     +0.0     +3.0
   -3dB    L50    -0.7     -8.3     +0.0     +2.3
   -3dB   L100     0.0     -inf     +0.0     +0.0
 -4.5dB      C    -4.5     -4.5     -1.5     +1.5
 -4.5dB    L50    -1.6    -10.2     -1.0     +1.2
 -4.5dB   L100     0.0     -inf     +0.0     +0.0
   -6dB      C    -6.0     -6.0     -3.0     +0.0
   -6dB    L50    -2.5    -12.0     -2.0     +0.0
   -6dB   L100     0.0     -inf     +0.0     +0.0

Read the table against a sound panned hard left, which every law leaves alone. The stereo column is what you hear from two speakers in a room, and the mono column is what happens when both sides are added together into one speaker.

• 0 dB (no compensation). Center is 3 dB louder in stereo and 6 dB louder in mono. You’ll mostly meet this on balance knobs, not true panners.
• −3 dB (constant power). Loudness stays even as you pan in stereo. Fold to mono and the center is 3 dB hotter than anything hard-panned.
• −6 dB. Perfect in mono, but in stereo the center dips 3 dB, so centered parts feel a bit too quiet on speakers.
• −4.5 dB. The compromise. Center is 1.5 dB down in stereo and 1.5 dB up in mono.

No law is right in both places at once. That’s the whole point: pick one, know which way it leans, and check the other way before you bounce.

Why your mix changes in mono

With a −3 dB law, mixing on speakers or headphones gives you a fair picture of the stereo balance. But a lot of playback is effectively mono: phone speakers, many Bluetooth speakers, club systems and some broadcast chains. In mono everything you put in the middle gets a 3 dB lift relative to anything panned hard, and parts at half-pan get about 2.3 dB. So the vocal, kick, snare and 808 move forward together, and the double-tracked guitars, wide pads and panned percussion step back.

Three decibels doesn’t sound like a lot until it’s the hats in a drill beat or the rhythm guitars in a rock mix. That’s the difference between a part that drives the song and one you have to look for. If your low end also lives in the center, mono makes the bass feel bigger too, which is one more reason a mix that’s balanced on headphones can sound heavy and narrow on a phone. We go into the phone side in why the 808 disappears on phone speakers.

The pan knob on a stereo track is usually a balance knob

In many DAWs, the single pan knob on a stereo track doesn’t move the sound anywhere. It turns the opposite side down. Push a stereo synth halfway left and you haven’t moved it, you’ve made its right channel quieter, and whatever was only on the right side is fading away. Hard left and the right channel is gone. If you want to move or narrow a stereo source, use a stereo panner or width control (many DAWs offer one on the track), or split it into two mono tracks and pan each one.

When pan law bites you in practice

1. Moving a session between DAWs. Open the same mix in an app with a different default law and every panned part shifts against the centered ones by a dB or more. If a collaborator says your session sounds different, check the pan law in both projects before you touch a fader.
2. Changing the law mid-mix. Most DAWs let you set it per project. Change it halfway through and your balance moves. Pick one at the start and leave it.
3. Summing stems somewhere else. Panning is printed into the stems, so they come back correctly. But if you send mono stems and let the mix engineer pan them, their law decides the balance, not yours. Our note on exporting stems for a mix engineer covers what to print.
4. Automating pans. A sweep from hard left to center with a −3 dB law is level in stereo but rises 3 dB in mono. If the move needs to be level everywhere, ride the volume a touch with it.

A quick routine that works

1. Find the pan law in your project settings, write it down, and keep it the same for the whole record.
2. Balance in stereo first. That’s how most people judge a mix.
3. Fold to mono at a low monitor level for ten seconds per section. Listen for which parts drop out, not for the whole mix getting smaller.
4. If a hard-panned part disappears, bring it a little toward center (70 to 80% often keeps the width and loses less in mono) or lift it 1 to 2 dB, then recheck stereo.
5. Bounce and measure the file, not the session. A low correlation reading is a separate problem from pan law, covered in phase correlation and mono.

Genre notes

• Hip-hop and trap. Vocal, kick and 808 in the middle get the mono lift, so hats and percussion panned hard are the first things to vanish on a phone. Keep the main hat closer to center and spread the extras.
• Rock and metal. Double-tracked guitars hard left and right are the sound of the genre, and they’re exactly what drops 3 dB in mono. Check that the riff still carries before you pull the vocal up.
• EDM and house. Club systems are often mono or close to it. Leads and stabs you widened with a balance knob can lose half their content. Use a real width tool and check it summed.
• Jazz and acoustic. Panning often mirrors where players stood. A gentler spread, around half-pan, keeps that picture in mono with only about a 2 dB shift.

What is pan law?

Pan law is the amount a mono sound is turned down on each side when it’s panned to the center, so it doesn’t get louder than when it’s panned hard. Common values are 0, −3, −4.5 and −6 dB.

Which pan law should I use?

−3 dB keeps stereo loudness even as you pan and is a common default. −6 dB keeps mono even instead, and −4.5 dB splits the difference. The best choice is the one you pick at the start and keep, then check the other way before you bounce.

Why do my panned instruments get quieter in mono?

With a −3 dB pan law, a centered sound adds up to 3 dB louder in mono than the same sound panned hard. So centered parts like the vocal and 808 come forward and hard-panned parts like guitars and hats fall back.

Is the pan knob on a stereo track a panner?

In many DAWs it’s a balance control. Turning it left lowers the right channel instead of moving the sound, so anything only on the right side fades out. Use a stereo panner or width control to move or narrow a stereo source.