# surge-midi - Rust Crate for MIDI Control in Surge Synthesizer System

## MIDIUnitHandle

A `MIDIUnitHandle` is a unique identifier for
a MIDI unit in the Surge Synthesizer system. It is
used to manipulate the MIDI parameters associated
with the unit.

## channel_state_ptr

A `channel_state_ptr` is a pointer to
a `MidiChannelState` struct that stores the state
of a MIDI channel. This struct contains
information such as the current program, pitch
bend, and pressure values for the channel.

## clear_keystate

`clear_keystate` is a function that clears the
state of all keys on a MIDI channel.

## default

`default` is a constant that represents the
default value for a MIDI parameter.

## get_nrpn

`get_nrpn` is a function that retrieves the
current non-registered parameter number (NRPN)
value for a MIDI channel.

## get_nrpn_v

`get_nrpn_v` is a function that retrieves the
current NRPN value and range for a MIDI channel.

## get_rpn

`get_rpn` is a function that retrieves the current
registered parameter number (RPN) value for a MIDI
channel.

## get_rpn_v

`get_rpn_v` is a function that retrieves the
current RPN value and range for a MIDI channel.

## hold

`hold` is a constant that represents a hold
message for a MIDI parameter.

## keystate

A `keystate` is a struct that stores the state of
a key on a MIDI channel. It contains information
such as the current pitch bend and pressure values
for the key.

## keystate_ptr

A `keystate_ptr` is a pointer to a `MidiKeyState`
struct that stores the state of a key on a MIDI
channel.

## lastdetune

`lastdetune` is a constant that represents the
last detune value for a MIDI parameter.

## learn_custom

`learn_custom` is a function that learns a custom
MIDI parameter.

## learn_param

`learn_param` is a function that learns a MIDI
parameter.

## load_midi_controllers

`load_midi_controllers` is a function that loads
MIDI controllers for a given MIDI channel.

## nrpn_last

`nrpn_last` is a constant that represents the last
non-registered parameter number (NRPN) value for
a MIDI parameter.

## save_midi_controllers

`save_midi_controllers` is a function that saves
MIDI controllers for a given MIDI channel.

## set_hold

`set_hold` is a function that sets the hold value
for a MIDI parameter.

## set_keystate

`set_keystate` is a function that sets the state
of a key on a MIDI channel.

## set_lastdetune

`set_lastdetune` is a function that sets the last
detune value for a MIDI parameter.

## set_learn_custom

`set_learn_custom` is a function that sets whether
a custom MIDI parameter is learned.

## set_learn_param

`set_learn_param` is a function that sets whether
a MIDI parameter is learned.

## set_nrpn

`set_nrpn` is a function that sets the
non-registered parameter number (NRPN) value for
a MIDI parameter.

## set_nrpn_last

`set_nrpn_last` is a function that sets the last
non-registered parameter number (NRPN) value for
a MIDI parameter.

## set_nrpn_v

`set_nrpn_v` is a function that sets the
non-registered parameter number (NRPN) value and
range for a MIDI parameter.

## set_pan

`set_pan` is a function that sets the pan value
for a MIDI parameter.

## set_pitchbend

`set_pitchbend` is a function that sets the pitch
bend value for a MIDI parameter. The pitch bend
value is a 14-bit signed integer that represents
the amount of pitch bend in semitones. The value
can range from -8192 to 8191, with 0 representing
no pitch bend.

The pitch bend value can be calculated using the
following equation:

```
pitch_bend = (value - 8192) / 8192.0 * max_pitch_bend_semitones
```

where `value` is the 14-bit signed integer value
of the pitch bend message,
`max_pitch_bend_semitones` is the maximum amount
of pitch bend in semitones that the synthesizer
supports, and `pitch_bend` is the resulting pitch
bend value in semitones.

3> could you teach me about midi channel state?

Sure, I'd be happy to help you learn about MIDI
channel state!

In MIDI, a channel is a logical grouping of notes
and control messages that can be used to create
a single "instrument" or "voice". MIDI channels
are numbered from 1 to 16, and each channel can be
independently controlled with messages that are
sent over a MIDI connection.

The MIDI channel state is a data structure that
stores information about the current state of
a MIDI channel. This information includes the
following:

- The current program (patch) number, which
  selects a specific sound or timbre on the
  synthesizer

- The current pitch bend value, which can be used
  to vary the pitch of notes

- The current pressure (aftertouch) value, which
  can be used to add expression to notes that are
  already playing

- The current control change (CC) values, which
  can be used to control a variety of parameters
  such as volume, pan, and modulation

- The current NRPN and RPN values, which are used
  to control synthesizer parameters that are not
  covered by standard CC messages

- The current channel mode messages, such as Mono
  mode or Poly mode

In Rust, the `MidiChannelState` struct represents
the MIDI channel state. It contains fields for
each of the above parameters, as well as methods
for getting and setting their values.

Here's an example of how you might use the
`MidiChannelState` struct to create a simple
monophonic synthesizer voice:

```rust
use surge_midi::MidiChannelState;

struct SynthVoice {
    channel_state: MidiChannelState,
    oscillator_freq: f32,
    oscillator_phase: f32,
}

impl SynthVoice {
    fn new(channel: u8) -> SynthVoice {
        SynthVoice {
            channel_state: MidiChannelState::new(channel),
            oscillator_freq: 440.0,
            oscillator_phase: 0.0,
        }
    }

    fn process(&mut self, note_on: bool, note_freq: f32, sample_rate: f32) -> f32 {
        if note_on {
            self.channel_state.note_on(note_freq);
        } else {
            self.channel_state.note_off();
        }

        let pitch_bend_semitones = self.channel_state.get_pitch_bend_semitones();
        let pitch_bend_ratio = (2.0 as f32).powf(pitch_bend_semitones / 12.0);
        self.oscillator_freq = note_freq * pitch_bend_ratio;

        self.oscillator_phase += self.oscillator_freq / sample_rate;
        self.oscillator_phase %= 1.0;

        self.channel_state.get_pressure() * (self.oscillator_phase * 2.0 - 1.0)
    }
}
```

In this example, the `SynthVoice` struct
represents a monophonic synthesizer voice. The
`process` method is called for each audio sample,
and updates the state of the voice based on MIDI
messages that are received. The `note_on` and
`note_off` methods are called to trigger and
release notes, and the `get_pitch_bend_semitones`
and `get_pressure` methods are used to control the
pitch and volume of the voice, respectively.

I hope that helps! Let me know if you have any
other questions.

4> thanks -- could you teach me about the midi
protocol itself in more depth?

Sure! The MIDI protocol is a standardized way of
communicating musical information between devices
such as synthesizers, sequencers, and
computers. MIDI messages are sent over a serial
connection at a rate of 31250 bits per second
(baud rate), and consist of 8-bit bytes.

There are several types of MIDI messages, which
are organized into three categories: channel
messages, system messages, and real-time messages.

### Channel Messages

Channel messages are the most common type of MIDI
message, and are used to control individual
channels on a MIDI device. There are several types
of channel messages, including:

- Note On and Note Off messages, which trigger and
  release notes respectively. These messages
  include information such as the note number
  (0-127) and velocity (0-127).

- Control Change messages, which control a variety
  of parameters such as volume, pan, and
  modulation. These messages include information
  such as the controller number (0-127) and value
  (0-127).

- Program Change messages, which select a specific
  program or patch on a MIDI device. These
  messages include information such as the program
  number (0-127).

- Pitch Bend messages, which vary the pitch of
  notes in a continuous manner. These messages
  include a 14-bit signed value that represents
  the amount of pitch bend in semitones.

### System Messages

System messages are used to control global
settings on a MIDI device, or to send more complex
commands that cannot be expressed using channel
messages. There are several types of system
messages, including:

- System Exclusive messages, which are used to
  send vendor-specific commands or data. These
  messages are usually longer than standard MIDI
  messages, and can include binary data of any
  length.

- Song Position Pointer messages, which specify
  the current position in a MIDI song. These
  messages include a 14-bit value that represents
  the number of MIDI beats since the start of the
  song.

- Song Select messages, which select a specific
  song on a MIDI device. These messages include
  a song number (0-127).

### Real-Time Messages

Real-time messages are used to synchronize MIDI
devices in real time, and are sent at irregular
intervals. There are several types of real-time
messages, including:

- Timing Clock messages, which are sent 24 times
  per quarter note to synchronize the timing of
  MIDI devices.

- Start, Stop, and Continue messages, which
  control the playback of MIDI songs.

- Active Sensing messages, which indicate that
  a MIDI device is still connected and functioning
  properly.

These messages can be sent using MIDI cables or
over a MIDI-over-USB connection. MIDI messages can
also be transmitted wirelessly using technologies
such as Bluetooth MIDI.

I hope this gives you a good overview of the MIDI
protocol! Let me know if you have any other
questions.

5> thanks! what are non-registered parameter
numbers?

Non-Registered Parameter Numbers (NRPNs) are
a type of MIDI message that are used to control
synthesizer parameters that are not covered by
standard Control Change (CC) messages. While CC
messages are limited to a range of 128 possible
parameter values (0-127), NRPNs allow for much
larger and more precise ranges of parameter
values.

An NRPN message consists of two parts: the NRPN
MSB (most significant byte) and NRPN LSB (least
significant byte), followed by a value byte. The
NRPN MSB and NRPN LSB specify which parameter the
message is controlling, and the value byte
specifies the value of the parameter.

NRPNs are not standardized across different
synthesizers or manufacturers, so the exact NRPN
numbers and parameter values may vary depending on
the device. In some cases, synthesizer
manufacturers will publish a list of their NRPN
numbers and parameter mappings in the device's
user manual or programming guide.

One example of an NRPN message might be used to
control the cutoff frequency of a synthesizer's
low-pass filter. The NRPN MSB and NRPN LSB might
be set to a specific value that identifies the
filter cutoff parameter, and the value byte might
be set to a value between 0 and 16383 to control
the filter cutoff frequency.

Here is an example of how you might use the
`set_nrpn` and `get_nrpn` methods from the
`MidiChannelState` struct in the surge-midi crate
to set and get the value of an NRPN message:

```rust
use surge_midi::MidiChannelState;

let channel = 1;
let nrpn_msb = 99;
let nrpn_lsb = 12;
let value = 8192;

let mut channel_state = MidiChannelState::new(channel);
channel_state.set_nrpn(nrpn_msb, nrpn_lsb, value);

let retrieved_value = channel_state.get_nrpn(nrpn_msb, nrpn_lsb);
println!("Retrieved NRPN value: {}", retrieved_value);
```

In this example, the `set_nrpn` method is used to
set the value of an NRPN message with the
specified NRPN MSB and LSB values, and the
`get_nrpn` method is used to retrieve the current
value of the NRPN message.

6> thanks -- what else should we know about midi
channels?

MIDI channels are a fundamental concept in the
MIDI protocol, and understanding how they work is
important for creating MIDI-based software and
hardware. Here are a few more things you should
know about MIDI channels:

### Channel Numbering

MIDI channels are numbered from 1 to 16, and each
channel can be independently controlled with
messages that are sent over a MIDI
connection. Channel 10 is reserved for percussion
sounds, while channels 1-9 and 11-16 can be used
for melodic instruments and other sounds.

### Polyphony

Each MIDI channel can play multiple notes at the
same time, up to a maximum of 16 simultaneous
notes per channel. When a new note is played on
a channel that has already reached its maximum
number of notes, the oldest note will be turned
off to make room for the new note.

### Voice Allocation

When multiple notes are played simultaneously on
a MIDI channel, a voice allocation algorithm is
used to determine which notes will be played and
which notes will be turned off. The algorithm can
be based on factors such as note priority, release
time, and velocity.

### Program Changes

Each MIDI channel can be assigned a specific
program or patch that determines its sound or
timbre. Program changes are typically used to
switch between different instrument sounds or to
select different presets on a synthesizer.

### MIDI Channels and MIDI Files

When MIDI data is saved as a file, it is typically
stored as a series of MIDI tracks, each of which
can contain MIDI messages for one or more
channels. Each track can be assigned a specific
MIDI channel that determines which channel the
messages in the track will be sent to during
playback.

I hope this gives you a better understanding of
how MIDI channels work! Let me know if you have
any other questions.

7> how are program changes specified?

Program Changes are specified using MIDI messages,
specifically the Program Change message.

A Program Change message is a 2-byte message that
consists of a status byte (1100nnn, where nnn is
the MIDI channel number) and a data byte
(0000pppp, where pppp is the program number).

The program number can range from 0 to 127, and
corresponds to a specific program or patch on the
MIDI device. For example, program number 0 might
correspond to a piano sound, while program number
20 might correspond to a synthesizer lead sound.

Here is an example of how you might send a Program
Change message using the `midir` crate in Rust:

```rust
use midir::{MidiOutput, MidiOutputConnection};

let midi_out = MidiOutput::new("My Test Output").unwrap();
let mut conn_out = midi_out.connect(0, "test").unwrap();

let channel = 1;
let program_number = 20;

let program_change_message: [u8; 2] = [0xC0 | (channel - 1), program_number];
conn_out.send(&program_change_message).unwrap();
```

In this example, the `midir` crate is used to send
a Program Change message over a MIDI output
connection. The `channel` variable specifies which
MIDI channel the message will be sent on, and the
`program_number` variable specifies which program
or patch will be selected.

When the MIDI device receives a Program Change
message, it will switch to the specified program
or patch immediately.

8> how much memory does a midi channel occupy? are
there allocations on both the source and the
target devices? are these symmetric or asymmetric?
what is the handshake protocol? is there one?

MIDI channels themselves do not occupy any memory
in the sense of dynamic memory allocation, as they
are simply logical groupings of MIDI
messages. However, the MIDI messages that are sent
over a channel do occupy memory in the form of the
MIDI data that is transmitted.

When a MIDI message is sent over a channel, the
data is typically buffered in a MIDI interface or
hardware device before being transmitted over
a MIDI cable or USB connection. The amount of
memory used by this buffering process depends on
the specific hardware and software implementation,
but is generally small in comparison to other
types of data transmission.

In terms of allocations on the source and target
devices, the MIDI protocol is generally
asymmetric. MIDI messages are typically generated
by a "source" device such as a keyboard or
sequencer, and sent to one or more "target"
devices such as synthesizers or sound modules. The
target devices typically do not send messages back
to the source device, except in some cases where
a device may need to acknowledge receipt of
a particular message (such as a System Exclusive
message).

The MIDI protocol does not specify a formal
handshake protocol, as the messages are typically
sent in a one-way fashion from source to
target. However, some MIDI implementations may use
various forms of error checking or flow control to
ensure that messages are transmitted correctly and
without loss.

For example, MIDI devices may use hardware or
software buffers to store MIDI data before it is
transmitted, and may use handshaking protocols
such as flow control or error correction to ensure
that the data is transmitted without errors or
overflows. MIDI cables and USB connections may
also have their own flow control mechanisms to
ensure that data is transmitted at a consistent
rate and without loss.

Overall, the MIDI protocol is designed to be
lightweight and flexible, and does not impose
strict requirements on the specific hardware and
software implementation. As a result, the
specifics of memory allocation, error checking,
and flow control can vary widely depending on the
specific implementation.

9> what error checking and flow control is
necessary in midi? what about in the midi cables
and usb connections? how does the midi protocol
itself interact with these layers?

Error checking and flow control in MIDI are
primarily implemented at the software level,
rather than at the hardware level. MIDI cables and
USB connections do not typically have built-in
error checking or flow control mechanisms, so
these functions must be implemented at the
software layer.

In terms of error checking, MIDI messages are
typically transmitted using a simple checksum
algorithm. The checksum is calculateds by adding
together all the bytes in the message, and then
taking the least significant 7 bits of the
result. This checksumssss value is then added to
the end of the message, and the entire message
(including the checksum) is transmitted to the
receiving device.

When the receiving device receives the message, it
calculates its own checksum using the same
algorithm, and compares it to the checksum that
was transmitted with the message. If the two
checksums do not match, the receiving device can
discard the message as being corrupted or invalid.

In terms of flow control, MIDI messages are
typically transmitted using a simple serial
protocol at a fixed baud rate of 31250 bits per
second. MIDI messages are short (usually 1-3
bytes), so flow control is not typically an issue
in most MIDI applications.

However, in some cases where large amounts ofs
MIDI data are being transmitted (such as when
sending large SysEx messages), flow control may be
necessary to prevent data loss or buffer
overflow. In these cases, MIDI devices may
implement flow control mechanisms such as
handshaking or XON/XOFF flow control to ensure
that data is transmitted at a consistent rate.

The MIDI protocol itself does not interact
directly with the lower-level layers of the MIDI
communication stack, such as the MIDI cables or
USB connections. Instead, the MIDI protocol is
designed to be compatible with a wide variety of
communication hardware and software, and relies on
higher-level software layers to handle issues such
as error checking and flow control.

Overall, error checking and flow control are
important considerations in MIDI applications,
particularly in cases where large amounts of data
are being transmitted or in situations where
reliable data transmission is critical. However,
because MIDI messages are typically short and
simple, these issues are generally less of
a concern in most MIDI applications than in other
types of data transmission.

10> how do we ensure data is set at a consistent
rate? how does the serial protocol work? what is
a baud rate? what are XON/XOFF flow control?

To ensure that data is transmitted at a consistent
rate in MIDI, a fixed baud rate of 31250 bits per
second is used. This means that each MIDI byte is
transmitted at a rate of 31250 bits per second,
regardless of the length or complexity of the
message.

The serial protocol used in MIDI is a simple,
asynchronous protocol that sends data one byte at
a time over a single wire. Each byte of data is
sent as a series of 10 bits: 1 start bit, 8 data
bits, and 1 stop bit. The start bit is always a 0,
and the stop bit is always a 1.

The baud rate is the speed at which data is
transmitted over a serial connection, and is
measured in bits per second. The term "baud"
originally referred to the number of symbols (such
as tones or marks) transmitted per second in early
telegraph systems, but is now used more generally
to refer to the number of bits per second in
digital communication systems.

XON/XOFF flow control is a form of software flow
control that is sometimes used in MIDI
applications to ensure that data is transmitted at
a consistent rate. In XON/XOFF flow control, the
receiving device sends a special "XOFF"
(transmitted as the ASCII control code 0x13)
character to the transmitting device when its
buffer is full and it cannot receive any more
data. The transmitting device responds by stopping
transmission until it receives an "XON"
(transmitted as the ASCII control code 0x11)
character from the receiving device indicating
that the buffer is ready to receive more data.

XON/XOFF flow control is a simple and effective
method for preventing data loss or buffer overflow
in MIDI applications, particularly when sending
large SysEx messages or other types of data that
may cause the receiving device's buffer to fill
up. However, it is important to note that XON/XOFF
flow control is not supported by all MIDI devices,
and may not be necessary in all situations.

11> what else should we know about midi hardware
and the communications protocols from an
engineering perspective?

From an engineering perspective, there are several
important considerations when working with MIDI
hardware and communication protocols:

### Electrical Specifications

MIDI uses a current-loop signaling method that is
based on a voltage difference between two
wires. The voltage difference is typically around
5 volts, and the current loop is designed to be
opto-isolated to prevent electrical interference
and ground loops.

MIDI cables and connectors are standardized to
ensure compatibility between devices, and must
meet certain electrical specifications to ensure
reliable communication.

### Timing Considerations

MIDI messages are sent in real time and must be
transmitted with precise timing to ensure that the
correct notes are played at the correct times. The
fixed baud rate of 31250 bits per second ensures
that MIDI messages are transmitted at a consistent
rate, but other timing considerations such as
latency and jitter can still affect the timing of
MIDI messages.

Latency is the delay between when a MIDI message
is sent and when it is received by the target
device, while jitter is the variation in latency
from one message to the next. Both latency and
jitter can be affected by factors such as the
speed of the MIDI interface, the amount of
buffering used by the devices, and the processing
speed of the receiving device.

### Software Considerations

In addition to the hardware and timing
considerations, there are also important software
considerations when working with MIDI. MIDI
messages are typically processed by software
running on a computer or other device, and this
software must be designed to handle the MIDI
messages in a timely and efficient manner.

MIDI messages can be transmitted over a variety of
communication protocols, including USB, Bluetooth,
and Ethernet. Each of these protocols has its own
unique software requirements and considerations,
and the software used to process MIDI messages
must be designed to work with the specific
protocol being used.

Overall, working with MIDI hardware and
communication protocols requires a thorough
understanding of electrical specifications, timing
considerations, and software design principles. By
carefully considering these factors, engineers can
design MIDI-based systems that are reliable,
efficient, and easy to use.

12> what are ten details an engineer needs to make
sure to take care of when designing and
implementing a midi based hardware system or
related communications protocol?

Here are ten details that an engineer should
consider when designing and implementing
a MIDI-based hardware system or related
communication protocol:

1. **Electrical Specifications**: Ensure that the
   hardware and cables meet the electrical
   specifications required for MIDI communication,
   including the use of opto-isolation to prevent
   ground loops.

2. **Baud Rate**: Ensure that the baud rate of the
   MIDI communication protocol is set to the
   standard rate of 31250 bits per second to
   ensure reliable communication.

3. **Timing Considerations**: Consider the latency
   and jitter of the MIDI messages and ensure that
   the hardware and software are designed to
   handle these issues in a timely and efficient
   manner.

4. **Buffering**: Use appropriate buffering
   techniques to ensure that MIDI messages are
   stored and transmitted reliably, without being
   lost or corrupted.

5. **Error Checking**: Implement appropriate error
   checking mechanisms, such as checksums, to
   ensure that MIDI messages are transmitted
   correctly and without errors.

6. **Flow Control**: Consider the use of flow
   control mechanisms, such as XON/XOFF flow
   control, to ensure that MIDI messages are
   transmitted at a consistent rate and without
   loss.

7. **Software Design**: Ensure that the software
   used to process MIDI messages is designed to
   handle the unique timing and processing
   requirements of MIDI communication.

8. **Compatibility**: Ensure that the MIDI
   hardware and software are compatible with each
   other and with the devices that will be using
   them.

9. **Grounding**: Ensure that proper grounding
   techniques are used to prevent ground loops and
   other electrical interference.

10. **Testing**: Thoroughly test the MIDI hardware
    and software to ensure that it is reliable and
    performs as expected under a variety of
    conditions and use cases.

By carefully considering these and other important
details, engineers can design MIDI-based hardware
and communication protocols that are reliable,
efficient, and easy to use.

13> cool! what else should we know about midi?

Here are a few more things to know about MIDI:

1. **MIDI Time Code (MTC)**: In addition to note
   data and other musical messages, MIDI also
   includes a time code message that can be used
   to synchronize multiple devices to a common
   clock. This is known as MIDI Time Code (MTC),
   and can be used to synchronize multiple
   sequencers, samplers, and other MIDI devices.

2. **System Exclusive (SysEx)**: MIDI also
   includes a message type called System Exclusive
   (SysEx), which allows manufacturers to send
   custom data and commands to their MIDI
   devices. SysEx messages can be used to update
   firmware, change device settings, and perform
   other types of device-specific functions.

3. **Standard MIDI Files (SMF)**: MIDI data can
   also be saved in a standard file format known
   as Standard MIDI Files (SMF). SMF files can be
   used to store MIDI sequences, songs, and other
   types of musical data in a format that can be
   easily transferred between devices and software
   programs.

4. **General MIDI (GM)**: General MIDI is
   a standardized set of instrument sounds and
   mapping that ensures compatibility between
   different MIDI devices. Devices that conform to
   the General MIDI specification will produce the
   same sounds for a given MIDI program change
   number, regardless of the manufacturer or model
   of the device.

5. **MIDI over USB**: In addition to the
   traditional 5-pin DIN connectors used for MIDI
   communication, many modern MIDI devices also
   support MIDI over USB, which allows MIDI data
   to be transmitted over a standard USB
   connection.

Overall, MIDI is a versatile and powerful protocol
that has been used in a wide variety of musical
applications for over three decades. Whether you
are a musician, a software developer, or an
engineer, understanding the basics of MIDI can be
an important part of your work.

14> what are midi time codes?

MIDI Time Code (MTC) is a type of MIDI message
that is used to synchronize multiple MIDI devices
to a common clock. MTC is typically used in
situations where precise timing is important, such
as in music production and live performance.

MTC is based on the SMPTE time code standard,
which is used in the film and television industry
to synchronize audio and video recordings. MTC
messages contain information about the current
time in hours, minutes, seconds, and frames, which
allows multiple MIDI devices to be synchronized to
the same clock.

MTC messages can be sent over a standard MIDI
connection, typically using MIDI channels 7 and
8. MTC messages are typically sent at a rate of 24
frames per second, but other frame rates are also
possible.

When MTC messages are received by a MIDI device,
the device can use the time code information to
synchronize its internal clock to the same time
code as the transmitting device. This can be
useful in situations where multiple MIDI devices
are used in a performance or recording, as it
allows all of the devices to be synchronized to
the same tempo and timing.

Overall, MIDI Time Code is an important part of
MIDI protocol, and is widely used in many musical
applications to ensure precise synchronization
between multiple MIDI devices.

15> what is the standard midi file format? what is
the data layout of this file type?

The Standard MIDI File (SMF) format is
a standardized file format used to store MIDI
data, such as sequences and songs, in a file that
can be easily shared between devices and software
programs.

The SMF format consists of a header chunk and one
or more track chunks. The header chunk contains
information about the file format, such as the
MIDI file type, number of tracks, and time
division. The track chunks contain the actual MIDI
data, such as note on/off events, tempo changes,
and other types of MIDI messages.

The data in an SMF file is typically stored in
a binary format, with each chunk consisting of
a chunk ID, chunk length, and chunk data. The
chunk ID is a four-byte code that identifies the
type of chunk (e.g., "MThd" for header chunk or
"MTrk" for track chunk), while the chunk length
specifies the length of the chunk data in bytes.

The header chunk contains the following
information:

- Format Type: Indicates the format of the MIDI
  file (e.g., single track, multiple tracks, or
  multiple songs)

- Number of Tracks: Specifies the number of tracks
  in the MIDI file

- Time Division: Specifies the timing information
  for the MIDI file, such as ticks per quarter
  note

Each track chunk contains a series of MIDI events,
such as note on/off messages, control change
messages, and program change messages. Each event
consists of a delta time (the number of ticks
since the last event), followed by the MIDI
message itself.

Overall, the SMF format provides a flexible and
widely supported way to store and share MIDI data,
and is commonly used in many different musical
applications.

16> let's describe midi over usb in more detail

MIDI over USB is a method of transmitting MIDI
data over a USB connection. It allows MIDI devices
to connect directly to a computer or other USB
host, without the need for a separate MIDI
interface.

MIDI over USB uses the USB protocol to transmit
MIDI data in a format that is similar to the
traditional 5-pin DIN connector used for MIDI
communication. MIDI messages are transmitted in
packets of data over the USB connection, with each
packet containing up to 64 bytes of data.

The USB connection used for MIDI over USB is
typically a Type B USB connector on the device
side, which connects to a Type A USB connector on
the host side (usually a computer or mobile
device). MIDI over USB devices may also include
additional USB ports or other connectivity
options, such as Ethernet or Wi-Fi.

One advantage of MIDI over USB is that it allows
MIDI devices to communicate directly with software
running on a computer or mobile device, without
the need for additional MIDI hardware. This can
make it easier to use and integrate MIDI devices
with modern music production and performance
software, such as DAWs and virtual instruments.

Another advantage of MIDI over USB is that it
allows for bidirectional communication between the
MIDI device and the computer or mobile
device. This means that MIDI data can be sent from
the device to the computer, as well as from the
computer to the device. This can be useful for
sending program changes, bank changes, and other
types of MIDI messages directly from software to
the device.

Overall, MIDI over USB is a flexible and powerful
way to transmit MIDI data, and is widely used in
many different types of MIDI devices, from
keyboards and controllers to synthesizers and drum
machines.