# Digital I/O Availability

The availability of S/PDIF and ADAT ports depends on the Digital I/O
Mode setting and the current sample rate.

The GUI reflects this dynamically: ports that are unavailable at the
current sample rate or Digital I/O mode are shown with strikethrough
text in the routing window, and a tooltip explains why they are
unavailable. Mixer inputs connected to unavailable ports are similarly
indicated.

## Sample Rate Categories

- **Single-band**: 44.1, 48 kHz
- **Dual-band**: 88.2, 96 kHz
- **Quad-band**: 176.4, 192 kHz

At quad-band sample rates, the mixer is also unavailable — the mixer
window displays a message indicating this.

## Scarlett 3rd Gen 18i20

This model has S/PDIF In/Out (coaxial/RCA), Optical 1 In/Out, and
Optical 2 In/Out ports.

### S/PDIF RCA Mode (Default)

| Rate | S/PDIF In | S/PDIF Out | Optical 1 In | Optical 1 Out | Optical 2 In | Optical 2 Out |
|------|-----------|------------|--------------|---------------|--------------|---------------|
| Single | S/PDIF 1-2 | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 | - | ADAT 1-8 |
| Dual | S/PDIF 1-2 | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 | - | - |
| Quad | S/PDIF 1-2 | S/PDIF 1-2 | - | - | - | - |

### S/PDIF Optical Mode

| Rate | S/PDIF In | S/PDIF Out | Optical 1 In | Optical 1 Out | Optical 2 In | Optical 2 Out |
|------|-----------|------------|--------------|---------------|--------------|---------------|
| Single | - | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 | S/PDIF 1-2 | S/PDIF 1-2 |
| Dual | - | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 | S/PDIF 1-2 | S/PDIF 1-2 |
| Quad | - | S/PDIF 1-2 | - | - | - | - |

### Dual ADAT Mode

| Rate | S/PDIF In | S/PDIF Out | Optical 1 In | Optical 1 Out | Optical 2 In | Optical 2 Out |
|------|-----------|------------|--------------|---------------|--------------|---------------|
| Single | - | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 | - | ADAT 1-8 |
| Dual | - | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 | ADAT 5-8 | ADAT 5-8 |
| Quad | - | S/PDIF 1-2 | - | - | - | - |

## Scarlett 4th Gen 16i16 and 18i16

These models have S/PDIF In/Out (coaxial/RCA) and Optical In/Out
ports.

### ADAT Mode

| Rate | S/PDIF In | S/PDIF Out | Optical In | Optical Out |
|------|-----------|------------|------------|-------------|
| Single | S/PDIF 1-2 | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 |
| Dual | S/PDIF 1-2 | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 |
| Quad | S/PDIF 1-2 | S/PDIF 1-2 | - | - |

### Optical S/PDIF Mode

| Rate | S/PDIF In | S/PDIF Out | Optical In | Optical Out |
|------|-----------|------------|------------|-------------|
| Single | - | S/PDIF 1-2 | S/PDIF 1-2 | S/PDIF 1-2 |
| Dual | - | S/PDIF 1-2 | S/PDIF 1-2 | S/PDIF 1-2 |
| Quad | - | S/PDIF 1-2 | - | - |

## Scarlett 4th Gen 18i20

This model has S/PDIF In/Out (coaxial/RCA), Optical 1 In/Out, and
Optical 2 In/Out ports.

### RCA S/PDIF Mode

| Rate | S/PDIF In | S/PDIF Out | Optical 1 In | Optical 1 Out | Optical 2 |
|------|-----------|------------|--------------|---------------|-----------|
| Single | S/PDIF 1-2 | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 | - |
| Dual | S/PDIF 1-2 | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 | - |
| Quad | - | S/PDIF 1-2 | - | - | - |

### Optical S/PDIF Mode

| Rate | S/PDIF In | S/PDIF Out | Optical 1 In | Optical 1 Out | Optical 2 In | Optical 2 Out |
|------|-----------|------------|--------------|---------------|--------------|---------------|
| Single | - | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 | S/PDIF 1-2 | S/PDIF 1-2 |
| Dual | - | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 | S/PDIF 1-2 | S/PDIF 1-2 |
| Quad | - | S/PDIF 1-2 | - | - | - | - |

### Dual ADAT Mode

| Rate | S/PDIF In | S/PDIF Out | Optical 1 In | Optical 1 Out | Optical 2 In | Optical 2 Out |
|------|-----------|------------|--------------|---------------|--------------|---------------|
| Single | - | S/PDIF 1-2 | ADAT 1-8 | ADAT 1-8 | ADAT 9-16 | ADAT 9-16 |
| Dual | - | S/PDIF 1-2 | ADAT 1-4 | ADAT 1-4 | ADAT 5-8 | ADAT 5-8 |
| Quad | - | S/PDIF 1-2 | - | - | - | - |
