Connect one thing at a time: permission, output, profile, channel, then playback.

The signal path in plain language

When you use 303box with external hardware, the browser sits between the sequencer and the device. The site creates note, timing and control messages. The browser exposes the MIDI outputs it is allowed to access. You choose one output. 303box sends messages on a MIDI channel. The hardware must be listening to that same channel and must be configured to receive the type of data you are sending.

That means “the computer sees the device” is only the first checkpoint. Successful playback requires the entire path to agree.

1. The browser supports Web MIDI and permission is granted.
2. The intended device appears in the OUTPUT menu.
3. The correct 303box device profile is selected.
4. The bass channel matches the hardware receive channel.
5. The playback mode includes MIDI output.
6. The hardware is in a state where incoming MIDI produces sound.

Before touching 303box: simplify the hardware side

Start with one device and one cable path. Disconnect unused MIDI interfaces if they create duplicate names. Stop any DAW or utility that may be holding the same MIDI port. Make sure the instrument itself produces sound locally before testing browser MIDI. If the device is silent from its own keyboard or sequencer, 303box is not the first problem to solve.

If your device lets you choose a MIDI receive channel, note that value before opening the site. Do not assume a factory default if you have used the machine in another setup; channel settings often survive power cycles.

Step 1: Enable MIDI and inspect the output list

Press ENABLE MIDI. The browser may show a permission prompt. After access is granted, open the OUTPUT menu. The important question is not whether MIDI is “enabled” in general, but whether the exact physical destination appears here.

If the menu shows only a dash, reload after confirming the device is connected and powered. If the device was unplugged and reconnected, the browser may expose a new internal port identity. 303box attempts to recover by matching the device name when possible, but a clean selection is still the safest first step after a cable change.

Live MIDI port check: Confirm that the hardware’s selected MIDI control/input port is the same physical route shown in OUTPUT. Then match the hardware receive channel to BASS CH — and RHYTHM CH for the T-8 rhythm part. A device can appear connected but remain silent when the port or channel differs.

Step 2: Choose the device profile deliberately

The current hardware-oriented profiles are Roland T-8 and Behringer TD-3, plus an automatic choice when the output name is recognizable. The profile is not a magic driver. It tells 303box which musical assumptions are appropriate for that device family, including whether a rhythm channel exists and which transport options make sense.

If AUTO does not identify a port correctly, select the profile manually. A generic USB-MIDI interface may expose the interface name rather than the synth model, so automatic detection cannot always know what is connected on the far side of the cable.

Step 3: Match the bass channel

MIDI channels are numbered 1 through 16. A note sent on channel 2 will not trigger a device listening only on channel 1. This is one of the most common reasons a connection looks healthy while no sound is produced.

Use the BASS CH selector in 303box and make it match the receive channel configured on the hardware. Do not change several settings at once. If the device says it is receiving on channel 2, set 303box to 2 and test again before touching clock or transport.

The T-8 profile also exposes a rhythm channel because that device combines bass and rhythm parts. The TD-3 profile does not pretend there is a drum part on the synth; the workflow stays focused on bass notes.

Step 4: Understand playback modes

303box separates where the sound should go:

• BROWSER: hear the internal browser instrument only. No external MIDI performance is required.
• BROWSER + MIDI: hear the browser while sending the pattern to the selected MIDI output. This is useful when you want a visual/audio reference while checking hardware.
• MIDI ONLY: use the external instrument as the audible destination and keep the browser synth out of the way.

If hardware is silent, start with BROWSER + MIDI rather than MIDI ONLY. The browser sound confirms that the sequencer itself is running. Once the external device responds reliably, MIDI ONLY is useful for recording or performing without doubling the line.

T-8 workflow: bass and rhythm in one compact device

The T-8 profile is useful when you want a synchronized bass-and-rhythm sketch. Keep the test simple at first: verify bass notes before enabling extra transport behavior. Then confirm the rhythm channel separately. A successful bass path does not prove the rhythm channel is correct, because the two parts can listen on different channels.

Clock and start/stop options should be treated as session tools, not troubleshooting shortcuts. If notes do not arrive, enabling clock will not fix the note channel. First prove that a single running pattern reaches the bass part. Then add synchronization features one by one.

TD-3 workflow: focus on note phrasing and channel match

The TD-3 is a dedicated 303-style bass workflow, so the important path is simpler: output, profile, bass channel and note playback. 303box sends note events with different velocities for normal and accented steps and uses overlapping note timing for slide-oriented phrasing. The exact audible result still depends on the synth's own settings and implementation.

For a first test, use a pattern with clear rests and no slides. If that works, add accent. Then add one slide between two different pitches. This staged test tells you whether silence is a connection problem or whether a later expression detail is simply behaving differently than expected.

Clock and transport: useful, but not required for basic note playback

MIDI clock communicates tempo timing. Start/stop transport messages tell compatible gear when a sequence should begin or end. These are separate from note messages. A synth can receive notes perfectly while ignoring external clock, or it can follow clock while its note channel is mismatched.

When diagnosing a connection, keep clock and transport off until note playback is proven. Once notes work, enable clock if you want the device's own sequencer or tempo-aware behavior to follow 303box. Enable transport only if your hardware setup is meant to respond to external start/stop.

A disciplined troubleshooting sequence

1. Stop playback. Start from silence so old queued notes do not confuse the test.
2. Confirm local sound. Make sure the hardware itself can produce audio.
3. Enable MIDI once. Accept the browser permission if asked.
4. Inspect OUTPUT. Select the exact destination; do not leave it on “—”.
5. Select the profile. Use T-8 or TD-3 explicitly if AUTO is uncertain.
6. Match BASS CH. Read the hardware receive setting and copy that number.
7. Choose BROWSER + MIDI. This proves the sequencer is running while testing the external path.
8. Use a simple pattern. No slide, no unusual transport behavior, obvious rests.
9. Press play. If the browser sounds and hardware does not, the remaining problem is in output/channel/device reception, not the pattern engine.
10. Add features later. Clock, transport, slide and recording workflows come after basic notes work.

What to do when OUTPUT is empty

An empty output menu means 303box does not currently have a connected MIDI destination exposed by the browser. Check power, cable and browser permission. Close software that may have exclusive access to the port. Disconnect and reconnect the device, then reload the page. If the browser previously remembered a port that no longer exists, selecting the newly exposed output is more reliable than trusting an old saved identifier.

What to do when OUTPUT is correct but there is no sound

This is where channel mismatch becomes the prime suspect. Verify the device receive channel. Then verify BASS CH. If they match, confirm the playback mode includes MIDI. Next, confirm the hardware is not filtering incoming notes or expecting a different MIDI path. Only after these checks should you investigate clock, transport or expression behavior.

What PANIC is for

MIDI instruments can occasionally hold a note if playback is interrupted between note-on and note-off events. PANIC is a safety control for that situation. It clears queued output where possible and sends note-release/all-notes-off style cleanup to the active channel. It is not a connection test and it should not be required during normal playback.

Browser limitations and session reliability

Web MIDI support and permission behavior are browser-dependent. USB reconnection can change how a port is represented. Sleep, device power changes or another application taking the port can also interrupt a session. For an important recording, confirm the output and channel again before the take rather than assuming yesterday's browser state is still valid.

303box stores some routing preferences locally for convenience, but the physical MIDI port remains a live browser resource. A saved choice cannot force a disconnected device to exist.

Manual transfer is still a valid hardware workflow

You do not need live MIDI to use 303box productively. A readable pattern sheet can be faster than debugging a session when you only need to move sixteen steps. Program the notes, rests, octave moves, accents and slides manually on the device, then perform filter and envelope changes on the hardware itself.

This is why 303box treats the browser as a notebook rather than as the final instrument. MIDI is one route from idea to machine, not the only route.

Independent compatibility note

303box is not affiliated with Roland or Behringer. Device names are used to describe compatibility and workflow. Hardware behavior may change with firmware or user configuration. When a device-specific setting differs from this guide, use the current manufacturer manual and the settings shown on your own unit as the final reference.