View source for Sonic & Knuckles Collection/Technical information/Music and sound effects

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{{SCHG S3K}}

Note: All data is little endian unless stated otherwise.

==Music==
Music playback is handled by the external DLL <tt>MIDIOUT.DLL</tt>. Music tracks are stored in the DLL as "CMP" [[wikipedia:Resource (Windows)|resources]]. These can be converted to and from standard [[MIDI]] files using [[SKC-Midi]].

===API===
<tt>GetMidiInterface</tt> returns a pointer to a <tt>MidiInterfaceClass</tt> class. This class provides the following methods:

{|class="prettytable" style="width:auto;"
!Function||Description
|-
| <tt>BOOL init(HWND hwnd)</tt>
| Initialise the playback code. If playback reaches the end of a non-looping track, an [https://docs.microsoft.com/en-gb/windows/win32/winmsg/about-messages-and-message-queues?redirectedfrom=MSDN#application-defined-messages application-defined message] with an identifier of <tt>0x464</tt> is posted to the HWND supplied to this function.
|-
| <tt>BOOL loadSong(short id, unsigned int bgmmode)</tt>
| Loads the specified song into memory. Valid values for bgmmode are:
* 0 = FM Synthesizer
* 1 = General MIDI
|-
| <tt>BOOL playSong()</tt>
| Starts playback of the currently loaded song.
|-
| <tt>BOOL stopSong()</tt>
| Stops playback of the currently loaded song.
|-
| <tt>BOOL pauseSong()</tt>
| Pauses playback of the currently loaded song.
|-
| <tt>BOOL resumeSong()</tt>
| Resumes playback of the currently loaded song.
|-
| <tt>BOOL setTempo(unsigned int pct)</tt>
| Changes the tempo of the currently loaded song. The default tempo is 100.
|}


===Compression===
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===Format===
Once decompressed, tracks are stored using the following format:

{|class="prettytable" style="width:auto;"
!Offset||Type||Description
|-
| 0
| 4 bytes
| [[sega:MIDI#Time_Division|Time Division]].
|-
| 4
| 4 bytes
| Number of events.
|-
| 8
| 4 bytes
| Unknown.
|-
| 12
| 4 bytes
| Unknown.
|-
| 16
| 8 * (number of events) bytes
| Array of MIDI events (8 bytes each)
{| class="prettytable" style="width:auto;"
!  Offset || Type || Description
|-
| 0 || 4 bytes || [[sega:MIDI#Delta-Times|Event delta time]].
|-
| 4 || 3 bytes || Event data. The purpose depends on the event type.
|-
| 7 || 1 byte  || Event type. Can be one of the following values:
|-
|   || $00     || [[sega:MIDI#MIDI_Channel_Events|MIDI Channel Event]]. The event data contains the numeric value and parameters.
|-
|   || $01     || [[sega:MIDI#Set_Tempo|Tempo Event]]. The event data contains the sequence tempo in terms of microseconds per quarter-note.
|-
|   || $02     || Loop Start/End. The event data is unused.
|}
|}


==Sound effects==
Sound effects are stored in the <tt>SONIC3K.DS2</tt> file, in 8-bit unsigned Mono at 22kHz. This can be edited using [[SKCsnd]].

The file format consists of a 32-bit integer containing the number of sound effects, followed by an array of 32-bit integers containing the length of each sound effect in bytes. After this is the sound data as raw [[PCM]] for each sound effect stored sequentially until the end of the file.


==References==
<references />

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