[ Collapse ] Bluetooth audio degradation

Chaos

Adds turbulence to the link quality set by Distance.

At Chaos 0% failures spread evenly and the tone follows Distance alone.

Turn it up and the link drifts on its own: the tone brightens and dulls, dropouts arrive in clusters. At Chaos 100% the drift is twice as deep and its events twice as often as at 50%.

It also sets how often the link briefly recovers, and how often one channel alone gets worse. The two channels drift separately.

Disorder

Replays short chunks of recent audio in the wrong order. A digital scramble rather than a dropout or a repeat.

Packet sets the chunk size; Distance makes the scramble more likely.

Dropouts

Sets how much of the audio signal never arrives.

At low Distance the dropouts are short: around 12 ms, heard as a tick or a flutter. As Distance rises they stretch, up to roughly a third of a second.

Dropouts are the device’s main failure. Most Receiver controls shape how they sound: whether they fall silent or repeat, how long they last, and how they enter and leave.

It is also the only dial that can disconnect the link: above Dropouts 50% and Distance 80% the link can go silent for 0.5 to 1.5 seconds before it reconnects. Distance makes disconnects more frequent, never longer.

Link

Toggles the link on and off. Off, the link can buzz briefly before the audio drains away. On, it returns in about 60 ms, dark and gritty, and opens up to full over the next second.

It works at any Distance, including 0%.

What the link death sounds like is set in the Encoder and Receiver panels: PLC how long the drain runs, Codec and Packet the pitch of the buzz, and Reconnect how dark and gritty the return is.

Mix

Blends the degraded signal against the dry one. At 100% you hear only the failing link; lower it to keep clean audio underneath.

Output

Trims the processed signal, −12 to +12 dB, unity at 0.

Dropouts and bandwidth collapse take energy out of the signal, so a heavily degraded link sits quieter than the dry one. Bring it back up with Output.

Visualiser Strip

A graphic visualisation of the Bluetooth link.

Columns of pixels representing the link’s transmitted packets.

The height shows the codec’s bandwidth: as Distance rises, the codec gives up its top end and the picture gets shorter.

Dropouts can dim the pixels as packets get lost: a light scatter of dark pixels when one channel dropped out, and a faint after-image of the whole column when both did. With audio playing, only a complete disconnect goes fully black.

The strip draws what the device does to the audio, not a measurement of what comes out. That’s how it can tell a dropout from a stutter or a scramble, which would all look like the same hole on a spectrum analyser.

Readouts

Link: the link quality right now, 0% when the link is dead.

±: how far link quality is swinging over the last second. A steady link sits near zero; Chaos widens it.

Bandwidth: the codec’s bandwidth ceiling right now.

Colours

The pixels are coloured by audio level: near-black at complete silence, blue and teal when quiet, green at medium, and orange to white at the loudest.

Each failure tints the pixels its own colour.

DisconnectDropoutInterferenceDisorderStutterPotholeRecovery

Codec

Chooses which Bluetooth codec the device imitates.

SBC is the old generic Bluetooth sound: gritty, clicky, dark. Its bandwidth steps down in jumps rather than gliding, because the subbands switch off one at a time. It collapses furthest, down to 2.8 kHz at 44.1 kHz sessions, 3 kHz at 48 kHz.

AAC is the Apple and AirPods default, the most balanced of the three, and the only codec that pre-echoes and whose treble goes mono before its bass. It spawns the most Smear whistles and collapses to 4.6 kHz.

LC3 is the modern LE Audio codec: smooth and robust, with the least grit and collapse; it still holds 7 kHz at full Distance.

Muffle

The treble control: how far the top end is allowed to close as Distance rises. A codec running out of bits gives up its treble first.

At Muffle 100%, Distance can close the top end down to the codec’s floor, a frequency set by Codec.

Lo-Cut

Thins the bass as the link gets worse.

It starts at about Distance 40% and thins the bass up to 300 Hz. At Lo-Cut 0% the bass is never touched.

Crush

The digital grit of a codec running out of bits. Crush sets how far Distance cuts the bit depth. Bass and mids go down to the Codec’s floor: 5 bits on SBC, 6 on AAC, 7 on LC3. The treble above 2.7 kHz is starved harder: down to 2 bits on SBC, 3.5 on AAC, 5.8 on LC3.

Warble

The swirling, underwater sound of a badly encoded MP3: eight narrow bands of high frequencies drop and rise at random. Audio below 1.6 kHz is not affected.

From Distance 20%, Warble sets how deep and how often the bands dip.

Pre-Echo (AAC)

Places a ghost of every sharp attack in front of it. When AAC runs short of bits, an attack’s coding noise spreads backwards across its block: Collapse copies the attack’s first 4.5 ms, reverses them, and layers them into the 4.5 ms before it.

Pre-Echo sets how loud the ghosts get at Distance 100%.

Note: The device always delays the audio by 9 ms, on every codec, and reports it to Live, which compensates. Judge timing with Live’s preview off.

Smear

Adds short metallic whistles over the sound, known as codec birdies: an encoder running out of bits invents tones when it can no longer code the correct ones. Each is a single tone between 2.5 and 8 kHz that dies away over about 150 ms, up to six at a time.

Smear sets how many whistles Distance can bring; Codec scales it, most on AAC, fewest on SBC.

Mono

Sets the maximum of how far the stereo image can collapse by Distance 100%.

A failing link short of bandwidth drops stereo first, the Bluetooth mono fallback.

On AAC the high frequencies go mono first: cymbals and reverb centre while the low end keeps its stereo width. At Mono 100% and Distance 45% the high frequencies are fully mono but the low end is still 55% wide.

SBC and LC3 narrow evenly.

Buffer Depth

How sensitive the receiver’s buffer is to Distance.

The receiver keeps a reserve of decoded audio between the radio and the output. A deep reserve can compensate for failures that arrive while Distance is still low, but a smaller buffer can run dry almost immediately.

The higher the Buffer Depth value, the later the link starts failing.

Buffer Depth changes when the failures start, not how they sound. Hold Distance still and lower Buffer Depth: the link falls apart, the sound stays the same.

Packet

How long each failure lasts.

Bluetooth moves audio in packets. Packet sets their size and how much audio goes missing each time one is lost. It sets the length of every stutter, mute and scramble.

At Packet 50% events run at their calibrated length; at 0% about a third as long, a fast machine-gun chatter; at 100% three times as long, slow and lurching.

The total amount of failure stays the same: many short events or a few long ones.

Stutter

Sets the probability for a dropout to turn into stutter instead of going silent.

When a packet fails to arrive, the receiver has two choices: play nothing or repeat the last slice of audio.

Stutter 0% means every dropout stays a hard mute. At Stutter 35% about a third of the dropouts turn into stutter. At Stutter 100% nearly every dropout repeats, fewer as Distance rises, because a receiver with an empty buffer has nothing left to repeat.

PLC

How a dropout enters silence.

PLC is packet-loss concealment that defines what the receiver does with the dropout. Old, cheap receivers usually make hard cuts. Modern ones try to conceal the dropout.

At PLC 0% it simply mutes with a hard cut. Raising the amount fills the front of the dropout with a fading repeat of the audio that did arrive.

The Codec changes how long the fill lasts. Packet lengthens the repeated slice along with every other failure length, which lowers the pitch of that repeat.

Reconnect

How dark and gritty the link sounds when it comes back after a complete disconnect.

After a full disconnect, Bluetooth reconnects at the lowest quality the source and receiver can agree on, the codec’s floor, and climbs back up over about a second.

Reconnect sets how far below that floor the return starts: nothing at 0%; at 100% the first instant back has 62% less bandwidth and up to four and a half bits less resolution, heard as grit.

Only a full disconnect triggers it: on its own above Distance 80% with Dropouts above 50%, or by hand with the Link toggle.

Pothole (LC3)

A dropout that is repaired instead of lost.

LC3 can send a second, much coarser copy of the audio, so a missing packet is covered rather than lost. Nothing goes silent, but for a moment the sound degrades.

The top end falls to a twentieth and flickers, the stereo image collapses to nearly mono, and transients blur, for 100 to 450 ms at Packet 50%.

Pothole sets how often a loss is repaired this way; Distance sets how deep, reaching full depth at Distance 50%.

Catch-Up

How the receiver catches back up after a dropout.

After a dropout the receiver plays behind, so the audio speeds up 3% to 6% to catch up: half a semitone to a semitone higher.

Catch-Up decides which dropouts get that speed-up. Raise it and only shorter ones do, but each rise runs much longer.

Relay (SBC, AAC)

Which stereo channel is the weak one.

True wireless earbuds often work in a relay: the source talks to one bud, which forwards the audio signal to the other. The audio has to cross the air twice to reach the second one, so it fails first, fails harder and recovers last.

At Relay 0% both channels are treated the same. Negative values make the left the weak channel, positive values the right. At the extremes the weak channel loses about twelve times as much audio as the other, and its dropouts run about four times as long. The strong channel still loses a little, just as it would in a real pair.

Relay distributes failures between the channels, it does not add any: the total is the same wherever you set it. It is off on LC3, which gives each channel its own link.