> ## Documentation Index
> Fetch the complete documentation index at: https://comfytv.org/llms.txt
> Use this file to discover all available pages before exploring further.
# Audio Echo
> Add echo, slapback, or feedback repeats to a track — from a tight vocal double to canyon-sized reflections.
## What this node does
**Audio Echo** applies FFmpeg's `aecho` delay/echo filter (or a native feedback delay) to an audio track. You pick a **preset** or dial in your own delay time, feedback, and gain. Presets like `mountains` produce long, decaying reflections; `robot` and `doubled` are short slapback-style repeats.
It takes a `COMFYTV_AUDIO` snapshot (or a `COMFYTV_VIDEO`, whose audio track is used) and outputs processed `COMFYTV_AUDIO`. It has a ▶ **Run** (FFmpeg does the work). A source is required.
To feed native ComfyUI `AUDIO` in or out, insert a **Bridge** — see [bridges.md](https://github.com/jtydhr88/ComfyTV/blob/main/docs/bridges.md).
## When to use it
* Thicken a dry vocal with a short doubled slapback.
* Add spacious, decaying echoes for an ambient or cinematic feel.
* Create rhythmic feedback repeats that trail off over time.
## Parameters
### preset
Chooses the echo character. Options: `custom`, `feedback`, plus four built-in `aecho` recipes — `doubled`, `robot`, `mountains` (default), `mountains2` (two-tap). Pick `custom` to use the four manual sliders below; pick `feedback` to use a native feedback delay driven only by **delay\_ms** and **decay**.
### in\_gain
Input signal level fed into the echo, **0.0–1.0** (default **0.6**). Used only when `preset = custom`.
### out\_gain
Level of the echoed (wet) signal in the output, **0.0–1.0** (default **0.3**). Used only when `preset = custom`.
### delay\_ms
Delay time before the first repeat, in milliseconds, **1–90000** (default **1000**). Used by `custom` and `feedback`. Short values (a few ms) give slapback/robot tones; long values (hundreds of ms) give distinct echoes.
### decay
How much each repeat fades relative to the previous one, **0.01–1.0** (default **0.5**). Higher = longer, more sustained tails. Used by `custom` and `feedback`.
## Outputs
| Output | Type | Meaning |
| --------- | --------------- | ------------------------- |
| **audio** | `COMFYTV_AUDIO` | The echoed audio snapshot |
## Tips
* The built-in presets ignore the manual sliders — set **preset = custom** to hear your gain/delay/decay values.
* `feedback` mode only reads **delay\_ms** and **decay**; the gains do nothing there.
* Very short delays (under \~10 ms) start to sound like comb-filtering/robotic coloration rather than distinct echoes.
## Related nodes
* **Muse Reverb (FDN)** — for dense, smeared reverberation rather than discrete repeats.
* **Audio Convolve (IR)** — real-space reverb from an impulse response.
* **Audio Modulation** — chorus/flanger for a different kind of "thickening."