1. Separate the audio path from the MIDI path
A USB or MIDI connection carries note instructions. Listen through the instrument’s own headphone or audio output: MIDI does not automatically return its analog audio to the browser. Confirm that the device produces sound with its local controls or internal sequencer, then stop that sequencer.
Start with one device and one cable route. For a direct USB connection, select the device’s USB MIDI port in OUTPUT. If a DIN cable connects through a MIDI interface, the list may show the interface name rather than the synth model.
2. Match three selections to the device
| 303box control | Must match | Example |
|---|---|---|
| OUTPUT | The physical MIDI output route connected by your cable | TD-3 USB or the interface output leading to the TD-3 |
| DEVICE | The connected instrument’s profile | TD-3 for TD-3; T-8 for T-8 |
| BASS CH | The instrument’s MIDI receive channel | If the device receives on IN 2, choose BASS CH 2 |
A port and a channel are different. OUTPUT selects the route to an instrument; BASS CH selects channel 1–16 within that route. Check that the device’s selected MIDI input route and the browser output use the same physical connection, then match their channel numbers. Read the device’s current setting instead of assuming a factory default.
Press ENABLE MIDI and allow access if the browser asks. If OUTPUT shows only “—”, no destination has been selected; resolve that before continuing. A listed port alone does not prove that notes reach the instrument.
3. Run a controlled four-note test
Open C notes on steps 1, 5, 9 and 13
- Confirm the load. Choose Base Octave 2, Tempo 120 BPM and Tune 0. The test has no accents or slides.
- Choose BROWSER + MIDI. Leave SEND CLOCK and SEND START / STOP off. Keep the device’s own pattern stopped.
- Press PLAY in the 303 section. Expect four C notes per bar with gaps between them. Listen to browser and hardware separately; their timbres need not match.
- Press STOP. If hardware sustains a note, use PANIC and investigate the connection. PANIC does not establish a connection or save a pattern.
On a T-8, this validates only the bass channel. Test rhythm separately afterward by matching RHYTHM CH to the device’s rhythm receive channel. A TD-3 is a bass instrument; do not apply the T-8 rhythm-channel setup to it.
4. Follow the first failed observation
| Observation | Check first | What it does not prove |
|---|---|---|
| Browser is silent too | PLAY, browser volume, audio output and whether the example loaded | That hardware routing is broken |
| Browser plays; OUTPUT is empty | Browser Web MIDI support/permission, power, cable and system port visibility | That the instrument is faulty |
| OUTPUT selected; device silent | Physical route, receive channel, BASS CH and a MIDI playback mode | That live notes were actually sent and received |
| Device plays a different sequence | Its internal sequencer and the START / STOP setting | That its pattern memory was changed |
| Note order matches; tone differs | Hardware waveform, tuning, filter and envelope | That the MIDI notes are wrong |
| Live notes work; memory writing fails | The TD-3 lab’s input/output, SysEx and read checks | That live playback validates a memory write |
Change one setting at a time. If the port list is empty, check whether another MIDI application uses the same port. After reconnecting a cable, select the currently listed output again. If the issue persists, record browser/OS versions, exact port names and the visible error text; repeatedly resetting permissions and settings makes the failure harder to isolate.
5. Choose the next route after live notes work
Once the four notes play on the device, try the accent and slide examples separately. CLOCK carries tempo timing; START / STOP controls transport. Add them only when you intend to synchronize the device’s own sequencer, following its manual.
For memory transfer, continue to the TD-3 USB transfer lab. Backup, destination slot and read-back are separate checks there. Direct writing remains experimental; this guide does not claim a successful physical memory-write recording.
Sources and scope
The W3C Web MIDI API is the technical reference for messages, ports and browser permissions. Browser support and device receive settings can differ. 303box is independent of Roland and Behringer; use the manufacturer’s manual for model- and firmware-specific settings.