# BambooTracker Bank File (.btb) Format Specification
v1.3.0 - 2021-06-13

- All data are little endian.
- Unless otherwise noted, character encoding of string is ASCII.

---

## Header
| Type              | Field           | Description                                                               |
| ----------------- | --------------- | ------------------------------------------------------------------------- |
| string (16 bytes) | File identifier | Format string, must be `BambooTrackerBnk`.                                |
| uint32            | EOF offset      | Relative offset to end of file. i.e. File length - 18.                    |
| uint32            | File version    | Version number in BCD-Code. e.g. Version 1.3.0 is stored as `0x00010300`. |


## Instrument Section
| Type             | Field                     | Description                                   |
| ---------------- | ------------------------- | --------------------------------------------- |
| string (8 bytes) | Section identifier        | Must be `INSTRMNT`.                           |
| uint32           | Instrument section offset | Relative offset to end of instrument section. |
| uint8            | Instrument count          | Number of instruments.                        |

After instrument count, details of each instrument are described.

| Type             | Field                  | Description                                                                                                   |
| ---------------- | ---------------------- | ------------------------------------------------------------------------------------------------------------- |
| uint8            | Instrument index       | Index of the instrument.                                                                                      |
| uint32           | instrument offset      | Relative offset to end of the instrument details.                                                             |
| uint32           | Instrument name length | Length of instrument name.                                                                                    |
| string (N bytes) | Instrument name        | String of instrument name. Character encoding is UTF-8. If instrument name is not set, this field is omitted. |
| uint8            | Instrument type        | Type of the instrument. `0x00`: FM, `0x01`: SSG, `0x02`: ADPCM, `0x03`: Drumkit.                              |

The following data change depending on sound source of the instrument.


### FM
| Type  | Field              | Description                                                                                      |
| ----- | ------------------ | ------------------------------------------------------------------------------------------------ |
| uint8 | Envelope number    | Envelope number.                                                                                 |
| uint8 | LFO number         | Bit 0-6 is LFO number, and bit 7 is flag. If bit 7 is clear, it uses LFO.                        |
| uint8 | AL sequence number | Bit 0-6 is algorithm sequence number, and bit 7 is flag. If bit 7 is clear, it uses AL sequence. |
| uint8 | FB sequence number | Bit 0-6 is feedback sequence number, and bit 7 is flag. If bit 7 is clear, it uses FB sequence.  |

After FB sequence number, it repeats 9 operator's parameters for each operator (1-4).

| Type  | Field              | Description                                                                                                          |
| ----- | ------------------ | -------------------------------------------------------------------------------------------------------------------- |
| uint8 | AR sequence number | Bit 0-6 is attack rate sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses AR sequence.   |
| uint8 | DR sequence number | Bit 0-6 is decay rate sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses DR sequence.    |
| uint8 | SR sequence number | Bit 0-6 is sustain rate sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses SR sequence.  |
| uint8 | RR sequence number | Bit 0-6 is release rate sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses RR sequence.  |
| uint8 | SL sequence number | Bit 0-6 is sustain level sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses SL sequence. |
| uint8 | TL sequence number | Bit 0-6 is total level sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses TL sequence.   |
| uint8 | KS sequence number | Bit 0-6 is key scale sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses KS sequence.     |
| uint8 | ML sequence number | Bit 0-6 is multiple sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses ML sequence.      |
| uint8 | DT sequence number | Bit 0-6 is detune sequence number of the operator, and bit 7 is flag. If bit 7 is clear, it uses DT sequence.        |

| Type  | Field                               | Description                                                                                                                                                            |
| ----- | ----------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| uint8 | Arpeggio sequence number            | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses arpeggio sequence for all operators.                                                |
| uint8 | Pitch sequence number               | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses pitch sequence for all operators.                                                      |
| uint8 | Envelope reset flag                 | Flag for envelope reset. Bit 0 is for all operators, bit 1 is for operator 1 and bit 3 is for operator 4. If bit is set, envelope reset is enabled for correspondings. |
| uint8 | Operator 1 arpeggio sequence number | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 1 arpeggio sequence in FM 3ch expansion mode.                              |
| uint8 | Operator 2 arpeggio sequence number | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 2 arpeggio sequence in FM 3ch expansion mode.                              |
| uint8 | Operator 3 arpeggio sequence number | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 3 arpeggio sequence in FM 3ch expansion mode.                              |
| uint8 | Operator 4 arpeggio sequence number | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 4 arpeggio sequence in FM 3ch expansion mode.                              |
| uint8 | Operator 1 pitch sequence number    | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 1 pitch sequence in FM 3ch expansion mode.                                    |
| uint8 | Operator 2 pitch sequence number    | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 2 pitch sequence in FM 3ch expansion mode.                                    |
| uint8 | Operator 3 pitch sequence number    | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 3 pitch sequence in FM 3ch expansion mode.                                    |
| uint8 | Operator 4 pitch sequence number    | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses operator 4 pitch sequence in FM 3ch expansion mode.                                    |
| uint8 | Panning sequence number             | Bit 0-6 is panning sequence number, and bit 7 is flag. If bit 7 is clear, it uses panning sequence.                                                                    |


### SSG
| Type  | Field                      | Description                                                                                               |
| ----- | -------------------------- | --------------------------------------------------------------------------------------------------------- |
| uint8 | Waveform sequence number   | Bit 0-6 is waveform sequence number, and bit 7 is flag. If bit 7 is clear, it uses waveform sequence.     |
| uint8 | Tone/Noise sequence number | Bit 0-6 is tone/noise sequence number, and bit 7 is flag. If bit 7 is clear, it uses tone/noise sequence. |
| uint8 | Envelope sequence number   | Bit 0-6 is envelope sequence number, and bit 7 is flag. If bit 7 is clear, it uses envelope sequence.     |
| uint8 | Arpeggio sequence number   | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses arpeggio sequence.     |
| uint8 | Pitch sequence number      | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses pitch sequence.           |


### ADPCM
| Type  | Field                    | Description                                                                                           |
| ----- | ------------------------ | ----------------------------------------------------------------------------------------------------- |
| uint8 | Sample                   | Sample number.                                                                                        |
| uint8 | Envelope sequence number | Bit 0-6 is envelope sequence number, and bit 7 is flag. If bit 7 is clear, it uses envelope sequence. |
| uint8 | Arpeggio sequence number | Bit 0-6 is arpeggio sequence number, and bit 7 is flag. If bit 7 is clear, it uses arpeggio sequence. |
| uint8 | Pitch sequence number    | Bit 0-6 is pitch sequence number, and bit 7 is flag. If bit 7 is clear, it uses pitch sequence.       |
| uint8 | Panning sequence number  | Bit 0-6 is panning sequence number, and bit 7 is flag. If bit 7 is clear, it uses panning sequence.   |


### ADPCM Drumkit
| Type  | Field     | Description                 |
| ----- | --------- | --------------------------- |
| uint8 | Key count | The count of assigned keys. |

After key count, it repeats data of assigned key.

| Type  | Field         | Description                       |
| ----- | ------------- | --------------------------------- |
| uint8 | Key number    | Assigned key number.              |
| uint8 | Sample number | Sample number.                    |
| int8  | Key pitch     | Assigned key pitch.               |
| uint8 | Panning flags | Bit 0 is right and bit 1 is left. |


## Instrument Property Section
| Type            | Field                              | Description                                            |
| --------------- | ---------------------------------- | ------------------------------------------------------ |
| string (8bytes) | Seciton identifier                 | Must be `INSTPROP`.                                    |
| uint32          | Instrument property section offset | Relative offset to end of instrument property section. |

This section contains subsections of each instrument property.

| Type  | Field                 | Description                                            |
| ----- | --------------------- | ------------------------------------------------------ |
| uint8 | Subsection identifier | Identify subsection type. See table below for details. |
| uint8 | block count           | Number of property blocks.                             |

Subsection identifier is defined as:

| Value         | Subsection type                                                      |
| ------------- | -------------------------------------------------------------------- |
| `0x00`        | FM envelope                                                          |
| `0x01`        | FM LFO                                                               |
| `0x02`        | FM AL sequence                                                       |
| `0x03`        | FM FB sequence                                                       |
| `0x04`-`0x0C` | FM operator 1 sequences (in the order defined in instrument section) |
| `0x0E`-`0x15` | FM operator 2 sequences (in the order defined in instrument section) |
| `0x16`-`0x1E` | FM operator 3 sequences (in the order defined in instrument section) |
| `0x1F`-`0x27` | FM operator 4 sequences (in the order defined in instrument section) |
| `0x28`        | FM arpeggio sequence                                                 |
| `0x29`        | FM pitch sequence                                                    |
| `0x2A`        | FM panning sequence                                                  |
| `0x30`        | SSG waveform sequence                                                |
| `0x31`        | SSG tone/noise sequence                                              |
| `0x32`        | SSG envelope sequence                                                |
| `0x33`        | SSG arpeggio sequence                                                |
| `0x34`        | SSG pitch sequence                                                   |
| `0x40`        | ADPCM sample                                                         |
| `0x41`        | ADPCM envelope sequence                                              |
| `0x42`        | ADPCM arpeggio sequence                                              |
| `0x43`        | ADPCM pitch sequence                                                 |
| `0x44`        | ADPCM panning sequence                                               |

 And repeats sequence data block.


### FM Envelope
| Type  | Field  | Description                                           |
| ----- | ------ | ----------------------------------------------------- |
| uint8 | Index  | Envelope index number.                                |
| uint8 | Offset | Relative offset to end of the envelope block.         |
| uint8 | AL/FB  | High nibble is algorithm, and low nibble is feedback. |

After this, repeat parameters in the table below for each operator.

| Type  | Field     | Description                                                                                       |
| ----- | --------- | ------------------------------------------------------------------------------------------------- |
| uint8 | Enable/AR | Flag which the operator is enabled when bit 5 is set, and attack rate is bit 0-4.                 |
| uint8 | KS/DR     | Bit 0-4 is decay rate, and bit 5-6 is key scale.                                                  |
| uint8 | DT/SR     | Bit 0-4 is sustain rate, and bit 5-7 is detune.                                                   |
| uint8 | SL/RR     | Low nibble is release, and High nibble is sustain level.                                          |
| uint8 | TL        | Total level.                                                                                      |
| uint8 | SSGEGs/ML | Low nibble is multiple, high nibble is type of SSGEG. If SSGEG is disabled, high nibble is `0x8`. |


### FM LFO
| Type  | Field         | Description                                                                                                                                                      |
| ----- | ------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| uint8 | Index         | LFO index number.                                                                                                                                                |
| uint8 | Offset        | Relative offset to end of the LFO block.                                                                                                                         |
| uint8 | Frequency/PMS | High nibble is LFO moduletion frequency, and low nibble is phase modulation sensitivity.                                                                         |
| uint8 | AMops/AMS     | high nibble is AM operator flags and low nibble is amplitude modulation sensitivity. Bit 4 is operator 1 and bit 7 is operator 4. If flag is set, AM is enabled. |
| uint8 | Start count   | Tick wait count before beginning LFO.                                                                                                                            |


### ADPCM sample
| Type      | Field         | Description                                              |
| --------- | ------------- | -------------------------------------------------------- |
| uint8     | Index         | Sample index number.                                     |
| uint32    | Offset        | Relative offset to end of the sample block.              |
| uint8     | Root key      | Root key number.                                         |
| uint16    | Root delta-N  | Delta-N (sample rate) in root key.                       |
| uint8     | Repeat flag   | If bit 0 is set, this ADPCM sample is played repeatedly. |
| uint32    | Sample length | Length of ADPCM sample.                                  |
| uint8 x N | Sample        | Raw ADPCM sample is stored.                              |


### Sequence
Sequence-type data block (e.g. FM arpeggio, SSG envelope) is defined as:

| Type   | Field           | Description                                   |
| ------ | --------------- | --------------------------------------------- |
| uint8  | Index           | Index number.                                 |
| uint16 | Offset          | Relative offset to end of the sequence block. |
| uint16 | Sequence length | Length of sequence.                           |

And repeat sequence data units.

| Type   | Field        | Description                                                                                                                            |
| ------ | ------------ | -------------------------------------------------------------------------------------------------------------------------------------- |
| uint16 | Unit data    | Value of unit. This also indicates row number of sequence editor. For details, see the subsection *Sequence Unit*.                     |
| int32  | Unit subdata | Unit subdata. Only used by SSG waveform and envelope, and omitted in other sequences. For details, see the subsection *Sequence Unit*. |

After sequences, loops are stored.

| Type   | Field       | Description      |
| ------ | ----------- | ---------------- |
| uint16 | Loop counts | Number of loops. |

Loop unit is defined as the table below. If it is stored `0x00` in loop counts i.g. there is no loop, the unit is omitted.

| Type   | Field        | Description                                                                             |
| ------ | ------------ | --------------------------------------------------------------------------------------- |
| uint16 | Begin point  | Count from head of sequence where loop starts.                                          |
| uint16 | End point    | Count from head of sequence where loop stops.                                           |
| uint8  | Repeat count | Count of loop repeating. Note: If `0x01` is stored, it is interpreted as infinity loop. |

There is release details in the end of subsequence block.

| Type   | Field         | Description                                                                                                                                                                 |
| ------ | ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| uint8  | Release type  | `0x00`: no release, `0x01`: fixed, `0x02`: absolute, `0x03`: releative. SSG envelope can be selected from all of these, and other properties can use only `0x00` or `0x01`. |
| uint16 | Release point | Count from head of sequence where loop starts. If release type is `0x00`, this field is omitted.                                                                            |

| Type  | Field         | Description                                    |
| ----- | ------------- | ---------------------------------------------- |
| uint8 | Sequence type | Type of sequence. See table below for details. |

Sequence type is defined as:

| Value  | Type      |
| ------ | --------- |
| `0x00` | Absolute. |
| `0x01` | Fixed.    |
| `0x02` | Relative. |

FM/SSG arpeggio can be selected from all of these, FM/SSG pitch can be absolute or relative, and other properties must be set to `0x00`.


#### Sequence Unit
In FM Operator sequence, unit data is the value of operator parameter.

In FM and SSG arpeggio, unit data has 2 interpretations depending on its sequence type:

- Absolute, Relative: Tone distance from the criterion 0.
- Fixed: Tone distance from C4.

In FM and SSG pitch, unit data is the tone distance from the criterion 0.

In SSG waveform, unit data represents the waveform:

| Unit data | Waveform                        |
| --------- | ------------------------------- |
| `0x00`    | Square                          |
| `0x01`    | Triangle                        |
| `0x02`    | Sawtooth                        |
| `0x03`    | Inversed sawtooth               |
| `0x04`    | Square-masked triangle          |
| `0x05`    | Square-masked sawtooth          |
| `0x06`    | Square-masked inversed sawtooth |

When waveform is square-masked, unit subdata is set one of the 2 types of data:

- If bit 16 is 0, it is raw data. Bit 0-11 is square mask period.
- If bit 16 is 1, it is tone/mask ratio. Bit 0-7 is mask part and bit 8-15 is tone part.

The other waveform set unit subdata to `-1`.

In SSG tone/noise, unit data defined as:

| Unit data     | Type                                               |
| ------------- | -------------------------------------------------- |
| `0x00`        | Tone.                                              |
| `0x01`-`0x20` | Noise. The period is set as `value` - 1.           |
| `0x21`-`0x40` | Tone & Noise. Noise period is set as `value` - 33. |

In SSG envelope, unit data defined as:

| Unit data     | Type                                                                                     |
| ------------- | ---------------------------------------------------------------------------------------- |
| `0x00`-`0x0F` | Software envelope. The value represents SSG channel volume. Unit subdata is set as `-1`. |
| `0x10`-`0x17` | Hardware envelope. The envelope shape number is specified as `value` - 16.               |

When unit data is set to use hardware envelope, unit subdata is set one of the 2 types of data:

- If bit 16 is 0, it is raw data. Bit 0-15 is hardware envelope period.
- If bit 16 is 1, it is tone/hard ratio. Bit 0-7 is hard part and bit 8-15 is tone part.

---

## History
| Version | Date       | Detail                                                                                          |
| ------- | ---------- | ----------------------------------------------------------------------------------------------- |
| 1.3.0   | 2021-06-13 | Added FM/ADPCM panning sequence, drumkit panning, and removed unused subdata of ADPCM envelope. |
| 1.2.0   | 2020-04-28 | Added ADPCM drumkit instrument.                                                                 |
| 1.1.0   | 2020-02-25 | Added ADPCM instrument.                                                                         |
| 1.0.2   | 2019-12-16 | Revised to fix the deep copy of instrument sequence types.                                      |
| 1.0.1   | 2019-11-09 | Reversed SSG noise pitch order.                                                                 |
| 1.0.0   | 2019-07-14 | Initial release.                                                                                |
