Docs Audio
Transitions
A transition is one track beginning as another ends. In NOT Cable the transition is mixed inside the broadcast engine, not at the receiver. Every point hears one single stream and none of them mixes on its own.
There are two separate mechanisms. Crossfading decides how tracks join, and the gap killer decides what happens to silence at the head and tail of a track.
This is what it looks like in Studio.
Crossfading#
The crossfade point is found in one of two ways.
Auto detect looks for the place where the level at the end of a track falls below a set threshold. The default threshold is -11 dB. It follows the natural ending of a song, which makes it the right choice most of the time.
Fixed time starts a set distance back from the end of the track. The default is 3 seconds.
| Setting | Default | What it does |
|---|---|---|
| Crossfade point | Auto detect | Threshold method or fixed time |
| Fixed time | 3.0 sec | Where the fade starts in fixed mode |
| Auto trigger | -11 dB | Where the tail falls below this level |
| Minimum overlap | 1000 ms | The next track starts at least this early |
| Maximum overlap | 3000 ms | Overlap never exceeds this |
| Curve | Equal power | Equal power or linear |
| Short-track limit | 15 sec | Tracks shorter than this never fade |
Minimum and maximum overlap work together. Even if the threshold is found early the overlap does not exceed the maximum, and even if it is found late it does not fall below the minimum.
The equal power curve holds total loudness steady across the transition. A linear curve leaves a dip in the middle. For music, equal power is usually the right one.
Fade out and fade in#
The crossfade point only decides when the next track starts. The ending track plays to its natural end unless a fade-out is explicitly asked for.
| Setting | Default |
|---|---|
| Fade out the ending track | Off |
| Fade in the next track | Off |
| Fade-in time | 800 ms |
Both are off by default. Most tracks have their own intro and their own tail; adding a fade on top of them makes the transition sound artificial.
Gap killer#
The gap killer trims silence at the head and tail of a track. This happens as the track is loaded, so the silence never reaches the air at all.
| Setting | Default | What it does |
|---|---|---|
| Silence from beginning | -30 dB | Intro below this threshold is trimmed |
| Silence from end | -35 dB | Tail below this threshold is trimmed |
| Skip blips | 10 ms | Sounds this short count as silence |
| End the song | 7 sec | This much silence ends the track early |
The head threshold is higher than the tail threshold, and that is deliberate. Song intros usually start harder, while tails fade away slowly.
Skipping blips stops a single tick at the start of a recording from breaking the silence. A sound that short does not count as presence.
The last row catches a long silence in the middle. If a recording has no sound for seven seconds, the track ends there. Setting zero turns that behaviour off.
When each applies#
The two mechanisms apply at different moments, and the difference matters.
Crossfade settings act on the broadcast currently playing. Move a slider and the next transition uses the new value.
Gap killer settings apply from the next track loaded onward. The track playing now was already loaded trimmed, and does not change retroactively.
The maths of the curve#
The equal-power curve keeps the sum of the squares of both gains constant
across the transition, where t is the progress from zero to one:
On a linear curve the gains are t and 1 - t. In the middle, at t = 0.5,
the sum of squares falls to 0.5:
That three-decibel dip in the middle is the drop you hear on a linear curve. Two unrelated pieces of music add as power, not as amplitude, which is why equal power is the correct one.
How overlap is bounded#
The crossfade point that is found is a proposal; it is clamped between two limits:
With the defaults that is between 1000 and 3000 milliseconds. Even if the threshold is found very early in the track the overlap never exceeds three seconds, and even if it is found very late it never falls below one.
Tracks shorter than fifteen seconds never fade at all. A jingle or a short announcement is not longer than the transition window itself.