How to use a line-in or audio interface with vizz.fm

What you need

Most modern laptops have no real line input, so a small USB audio interface is the reliable route. They are cheap, need no drivers, and give you a proper stereo line-level input with a gain knob.

Option 1: A USB audio interface

Any class-compliant USB interface works. If you already own one for recording, use it. Many DJ controllers and mixers (Pioneer, Numark, Denon, Native Instruments) are USB audio devices themselves. Plug one into the computer and it usually shows up as an input, no separate interface needed. Check whether its USB audio carries the master output or only the individual decks; you want the master mix.

Option 2: A built-in line-in jack

Desktop PCs usually have a dedicated line-in jack on the back, typically color-coded blue. That is a true stereo line-level input and works fine with a 3.5 mm cable. Older Macs (before roughly 2016) had one too.

Cables and adapters

• Mixers and consoles: usually RCA or 1/4-inch outputs. Use the “Record Out”, “Booth”, or a spare “Master” output if you have one, so the visualizer feed is independent of your main volume.
• Turntables: need a phono preamp. Plug the turntable into a mixer or a preamp first, then that into the interface. A bare turntable into a line input is very quiet and thin.
• Synths and drum machines: 1/4-inch outputs, usually mono per jack. A single cable is fine, or use both outputs into a two-input interface for stereo.
• Phones and small players: a 3.5 mm to RCA or 3.5 mm to 3.5 mm cable from the headphone output works, with the device volume around 70 to 80 percent.

Setup

Plug everything in, then confirm the operating system sees signal before you open the browser. Most problems show up at this step, where they are easy to fix.

Selecting it in vizz.fm

1. Open vizz.fm
2. Click the audio source button and choose Microphone
3. The browser asks which microphone to use. Pick your interface or “Line In” from the list
4. Play your source and the visualizer should react immediately

Getting the level right

A line input is usually quieter than a laptop mic, which gets automatic gain from the operating system, so the first impression is often “it barely moves”. The connection is fine; the level is low. Work from the source toward the browser:

1. Source volume. Set the mixer's record or booth output, or the device's headphone volume, to a healthy level, short of maximum.
2. Interface gain. Raise the gain knob until the interface's signal light is green on peaks and never red. No signal light? Use the OS input meter.
3. OS input level. Aim for peaks around two-thirds of the meter in Sound settings.
4. vizz.fm sensitivity. Finally, adjust the Global Sensitivity slider in the app to taste. It is a final trim. It cannot rescue a whisper-quiet signal.

If the visuals look pinned at maximum no matter what, the signal is clipping somewhere. Back off in the same order: source first, then interface gain.

Troubleshooting

• Constant hum or buzz. Almost always a ground loop, usually when the source and the computer are on different power outlets or the laptop is charging. Try running the laptop on battery to confirm. A cheap inline ground loop isolator on the RCA or 3.5 mm cable fixes it for good.
• Distorted or crackly. A line-level signal going into a mic-level jack (the laptop combo jack), or the interface gain too high. Lower the source, or switch to a real line input.
• Only one channel. A mono cable in a stereo jack, or a single synth output. Usually harmless for visualizing, since the app reacts to the overall signal, but a stereo cable or a second input fixes it.
• Device missing from the browser list. Reload the page after plugging the interface in; browsers only refresh the device list on a new permission request or reload. Also check the OS sees it first.
• Works in the OS meter but not in the browser. Another app has exclusive control of the device. Close your DAW or DJ software, or turn off exclusive mode in the device's Windows properties (Advanced tab).
• Sounds fine but reacts late. If you are listening through the interface's direct monitor, you hear the audio a few milliseconds before the computer does. That small offset is normal, and an audience listening to the same speakers as the visuals will not notice it.

See your mixer in real time.

No downloads, no sign-up. Open the app, pick your interface as the microphone, and go.

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