ENVO

“Just right” isn’t really about the volume of your podcast. It is about the gap between the podcast and everything else in the room. When the room gets louder, the noise floor rises and swallows that gap: suddenly you can’t make out the words, even though the podcast is playing exactly as loud as before.

So what you want isn’t constant volume. You want a constant gap. And that means the volume has to move: up when the world gets loud, back down when it quiets. Ten times a second ENVO measures your surroundings, and once a second it decides whether to act. Your chosen level is always the baseline: touch the volume buttons and that becomes the new baseline. You are never fighting the app.

How loud a room is and how much of your audio it buries are two different questions. ENVO splits the signal into six octave bands from 125 Hz to 4 kHz, spreads each band’s level upward at 12 dB per octave, because a low drone also masks the bands above it, and weights the result after ANSI S3.5: by where speech carries its information. An A-weighting would all but overlook the drone of a train. ENVO doesn’t.

Like a camera’s light meter, ENVO never keeps the picture: a single number is computed from the microphone, and the audio is thrown away instantly.

ENVO reasons in decibels, the language your ear speaks: about 0.5 dB of volume per dB of room change, never further than ±3, ±6 or ±9 dB from your baseline. iOS only moves the system volume in steps of roughly 3 dB, and ENVO’s intent changes by at most 0.75 dB per second. Steps are therefore infrequent, and never rapid.

Your own music. The microphone hears your speaker too, and a naive app would turn itself up. So ENVO measures the noise floor in the quiet moments between beats and words, as the L90 of the last 10 to 60 seconds, and learns from its own volume steps how much of it comes from the device.

Rising voices. As a restaurant fills, everyone talks louder and the room climbs into a roar (the Lombard effect). ENVO recognises speech-shaped noise by its spectrum and syllable rate and follows it by up to 3 dB less. Engines, ventilation and traffic get the full response.

The door. Brief spikes are clipped against the median before they reach the floor. A louder room counts, a hand clap doesn’t.

1. 01A hard ceiling at 92% system volume, for ENVO’s own contribution only.
2. 02Never further than ±3, ±6 or ±9 dB from your baseline.
3. 03Never more than a quarter of the slider’s travel, five hardware steps.
4. 04At most 0.75 dB of change per second.
5. 05Your baseline always wins.
6. 06Reverts on its own and lands exactly on zero.
7. 07Doesn’t follow the Lombard spiral.
8. 08Spikes can’t trigger jumps.
9. 09Doesn’t listen to itself.
10. 10Never steers blind when the microphone drops out.
11. 11Says when it can’t measure: pocket, covered, clipping.
12. 12Touches nothing when nothing is playing.
13. 13Admits when an output keeps its own volume.
14. 14Starts over when headphones come or go.

162 tests in the public source drive the shipping control law, not a re-implementation of it. What it says here is there to be read rather than taken on faith.

The input is compressed. iOS applies automatic gain control to the microphone. Measured on an iPhone 14 against a calibrated sound level meter, a real change of 20 dB reads as 15.6 dB. ENVO adapts usefully, not accurately.

Continuous music out loud sets a floor ENVO cannot see beneath: it returns you to your starting volume, but not below it. On headphones the full range applies.

The number on screen is a masking-weighted estimate with ±10 dB of uncertainty, not a dB(A) figure. As a relative measure it is useful; as an absolute measurement it is not.

RESPONSE

The noise-floor window: SLOW 60 s, MED 30 s, FAST 10 s.

RANGE

±3, ±6 or ±9 dB from your baseline. A leash length, not a sensitivity dial.

DIR

Increases only, decreases only, or both.

CALIBRATE

A room calibration of about 35 s with pink noise, or a 5-second refresh.

START / STOP

Before START, ENVO touches nothing.

AUTO-RESUME

Restart on launch if ENVO was running at last quit.

ENVO runs in the background with any audio app, keeps hi-fi stereo on your Bluetooth headphones and starts with Siri, the Action Button or Shortcuts. Headphones are its best case: there, the microphone hears the room, not your music.