# Banks and Selectors

> Original: [Bank support](https://tttapa.github.io/Control-Surface/Doxygen/db/dbd/classBank.html)

Banks allow a single physical control to address multiple MIDI parameters by switching the active bank.

## How banks work

`Bank<N>` manages N settings. Bankable elements compute their effective address as:

    effective_address = base_address + (bank_setting × offset)

The offset is set when constructing the bank, and the base address is set per-element.

```cpp pico
Bank<4> bank(2);  // 4 settings, offset 2 between each
```

With base address 16, the four banks produce addresses 16, 18, 20, 22.

## Bank types

- `BankType::ChangeAddress` — shifts the CC/note number
- `BankType::ChangeChannel` — shifts the MIDI channel

## Selectors

Selectors control which bank setting is active:

| Class | Description |
|-------|-------------|
| `EncoderSelector<N>` | Rotary encoder cycles banks |
| `IncrementDecrementSelector<N>` | Two buttons: up/down |
| `IncrementSelector<N>` | Single button, wraps around |
| `ManyButtonsSelector<N>` | One button per bank |
| `SwitchSelector` | Two-position toggle |
| `ProgramChangeSelector<N>` | Incoming MIDI PC selects bank |

```cpp pico
IncrementDecrementSelector<4> selector {bank, {2, 3}, Wrap::Wrap};
```

## Transposer

`Transposer<Min, Max>` is a specialized bank that offsets note numbers:

```cpp pico
Transposer<-12, 12> transposer;
IncrementDecrementSelector<25> transposeSelect {transposer, {2, 3}, Wrap::Clamp};
```

## Bankable input elements

All input elements (`CCValue`, `NoteLED`, etc.) have bankable variants:

```cpp pico
Bankable::CCValue<4> cc {{bank, BankType::ChangeAddress}, {16, Channel_1}};
```

## Bankable output elements

Bankable output elements (`Bankable::NoteButton`, `Bankable::CCPotentiometer`, etc.) are not yet implemented (Phase 11). Bank switching currently works with input elements and selectors only.