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Text File | 1996-02-23 | 16.8 KB | 360 lines

Impulse Header Layout 0 1 2 3 4 5 6 7 8 9 A B C D E F ┌───┬───┬───┬───┬───────────────────────────────────────────────┐ 0000: │'I'│'M'│'P'│'M'│ Song Name, max 26 characters, includes NULL │ ├───┴───┴───┴───┴───────────────────────────────────────┬───┬───┤ 0010: │.......................................................│ x │ x │ ├───────┬───────┬───────┬───────┬───────┬───────┬───────┼───┴───┤ 0020: │OrdNum │InsNum │SmpNum │PatNum │ Cwt/v │ Cmwt │ Flags │Special│ ├───┬───┼───┬───┼───┬───┼───────┼───────┴───────┼───┬───┼───┬───┤ 0030: │GV │MV │IS │IT │Sep│(0)│MsgLgth│Message Offset │ x │ x │ x │ x │ ├───┴───┴───┴───┴───┴───┴───────┴───────────────┴───┴───┴───┴───┤ 0040: │ Chnl Pan (64 bytes)...........................................│ ├───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┤ ├───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┤ 0080: │ Chnl Vol (64 bytes)...........................................│ ├───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┤ ├───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┤ 00C0: │ Orders, Length = OrdNum │ ├───────────────────────────────────────────────────────────────┤ xxxx: │ 'Long' Offset of instruments, Length = InsNum*4 (1) │ ├───────────────────────────────────────────────────────────────┤ xxxx: │ 'Long' Offset of samples headers, Length = SmpNum*4 (2) │ ├───────────────────────────────────────────────────────────────┤ xxxx: │ 'Long' Offset of patterns, Length = PatNum*4 (3) │ └───────────────────────────────────────────────────────────────┘ (1) Offset = 00C0h+OrdNum (2) Offset = 00C0h+OrdNum+InsNum*4 (3) Offset = 00C0h+OrdNum+InsNum*4+SmpNum*4 Note that if the (long) offset to a pattern = 0, then the pattern is assumed to be a 64 row empty pattern. Cwt: Created with tracker. Impulse Tracker y.xx = 0yxxh Cmwt: Compatible with tracker with version greater than value. OrdNum: Number of orders in song. InsNum: Number of instruments in song SmpNum: Number of samples in song PatNum: Number of patterns in song Flags: Bit 0: On = Stereo, Off = Mono Bit 1: Vol0MixOptimizations - If on, no mixing occurs if the volume at mixing time is 0 (redundant v1.04+) Bit 2: On = Use instruments, Off = Use samples. Bit 3: On = Linear slides, Off = Amiga slides. Special: Bit 0: On = song message attached. Song message: Stored at offset given by "Message Offset" field. Length = MsgLgth. NewLine = 0Dh (13 dec) EndOfMsg = 0 Bits 1-15: Undefined. GV: Global volume. (0->128) All volumes are adjusted by this MV: Mix volume (0->128) During mixing, this value controls the magnitude of the wave being mixed. IS: Initial Speed of song. IT: Initial Tempo of song Sep: Panning separation between channels (0->128, 128 is max sep.) Chnl Vol: Volume for each channel. Ranges from 0->64 Chnl Pan: Each byte contains a panning value for a channel. Ranges from 0 (absolute left) to 64 (absolute right). 32 = central pan, 100 = Surround sound. +128 = disabled channel (notes will not be played, but note that effects in muted channels are still processed) Orders: This is the order in which the patterns are played. Valid values are from 0->199. 255 = "---", End of song marker 254 = "+++", Skip to next order Impulse Instrument Format 0 1 2 3 4 5 6 7 8 9 A B C D E F ┌───┬───┬───┬───┬───────────────────────────────────────────────┐ 0000: │'I'│'M'│'P'│'I'│ DOS FileName (12345678.123) │ ├───┼───┼───┼───┼───┬───┬───┬───┬───────┬───┬───┬───────┬───┬───┤ 0010: │00h│Flg│VLS│VLE│SLS│SLE│ x │ x │FadeOut│NNA│DNC│TrkVers│NoS│ x │ ├───┴───┴───┴───┴───┴───┴───┴───┴───────┴───┴───┴───────┴───┴───┤ 0020: │ Instrument Name, max 26 bytes, includes NUL...................│ ├───────────────────────────────────────┬───┬───┬───┬───┬───┬───┤ 0030: │.......................................│ x │ x │ x │ x │ x │ x │ ├───────────────────────────────────────┴───┴───┴───┴───┴───┴───┤ 0040: │ Note-Sample/Keyboard Table, Length = 240 bytes................│ ├───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┤ ├───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┴───┤ 0130: │ Volume envelope (200 bytes)...................................│ ├───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┤ ├───┴───┴───┴───┴───┴───┴───┴───┤ 01F8: │ Node points (25x2 bytes)......│ └───────────────────────────────┘ Total length of an instrument header is 554 bytes. But for practical use in a player, it's better to load 504 bytes (up to 1F8h) into memory, load the extra 50 bytes into a temporary buffer and look up the node times (for VLS/VLE/SLS/SLE) during loadup (as opposed to during playback). Flg: Bit 0. On = Use volume envelope Bit 1. On = Use volume loop Bit 2. On = Use sustain volume loop VLS: Volume loop start (node number) VLE: Volume loop end (node number) SLS: Sustain loop start (node number) SLE: Sustain loop end (node number) FadeOut: Ranges between 0 and 64, but the fadeout "Count" is 512. See the Last section on how this works. Fade applied when: 1) Note fade NNA is selected and triggered (by another note) 2) Note off NNA is selected with no volume envelope or volume envelope loop 3) Volume envelope end is reached DNC: Duplicate note check (0 = Off, 1 = On) NNA: New note action: 0 = Note cut 1 = Note off 2 = Note continue 3 = Note fade TrkVers: Tracker version used to save the instrument. This is only used in the instrument files. NoS: Number of samples associated with instrument. This is only used in the instrument files. Note-Sample/Keyboard Table. Each note of the instrument is first converted to a sample number and a note (C-0 -> B-9). These are stored as note/sample pairs (note first, range 0->119 for C-0 to B-9, sample ranges from 1-99, 0=no sample) Volume envelope: Values from 0->64, 0FFh indicating end of envelope. (after which note fade applies) Node data: Tick THEN magnitude Impulse Sample Format 0 1 2 3 4 5 6 7 8 9 A B C D E F ┌───┬───┬───┬───┬───────────────────────────────────────────────┐ 0000: │'I'│'M'│'P'│'S'│ DOS Filename (12345678.123) │ ├───┼───┼───┼───┼───────────────────────────────────────────────┤ 0010: │00h│GvL│Flg│Vol│ Sample Name, max 26 bytes, includes NUL.......│ ├───┴───┴───┴───┴───────────────────────────────────────┬───┬───┤ 0020: │.......................................................│ x │ x │ ├───────────────┬───────────────┬───────────────┬───────┴───┴───┤ 0030: │ Length │ Loop Begin │ Loop End │ C5Speed │ ├───────────────┼───────────────┼───────────────┼───┬───┬───┬───┤ 0040: │ SusLoop Begin │ SusLoop End │ SamplePointer │ViS│ViD│ViR│ViT│ └───────────────┴───────────────┴───────────────┴───┴───┴───┴───┘ The cache file has the following pieces of information added on: 0 1 2 3 4 5 6 7 8 9 A B C D E F ┌───────────────┬───────┬───────┬───┬───────────────────────────┐ 0050: │ File Size │ Date │ Time │Fmt│...........................│ └───────────────┴───────┴───────┴───┴───────────────────────────┘ Fmt. 0 = unchecked. 1 = directory, 2 = it sample, 3 = st sample GvL: Global volume for instrument, ranges from 0->64 Flg: Bit 0. On = sample associated with header. Bit 1. On = 16 bit, Off = 8 bit. Bit 2. On = stereo, Off = mono. Stereo samples not supported yet Bit 3. Reserved Bit 4. On = Use loop Bit 5. On = Use sustain loop Bit 6. On = Ping Pong loop, Off = Forwards loop Bit 7. On = Ping Pong Sustain loop, Off = Forwards Sustain loop Vol: Default volume for instrument Length: Length of sample in no. of samples NOT no. of bytes LoopBeg: Start of loop (no of samples in, not bytes) Loop End: Sample no. AFTER end of loop C5Speed: Number of bytes a second for C-5 (ranges from 0->9999999) SusLBeg: Start of sustain loop SusLEnd: Sample no. AFTER end of sustain loop SmpPoint: 'Long' Offset of sample in file. ViS: Vibrato Speed, ranges from 0->64 ViD: Vibrato Depth, ranges from 0->64 ViT: Vibrato waveform type. 0=Sine wave 1=Ramp down 2=Square wave 3=Random (speed is irrelevant) ViR: Vibrato Rate, rate at which vibrato is applied (0->64) The depth of the vibrato at any point is worked out in the following way: Every processing cycle, the following occurs: 1) Mov AX, [SomeVariableNameRelatingToVibrato] 2) Add AL, Rate 3) AdC AH, 0 4) AH contains the depth of the vibrato as a fine-linear slide. 5) Mov [SomeVariableNameRelatingToVibrato], AX ; For the next ; cycle. For those that don't understand assembly, then the depth is basically the running-sum of the rate divided by 256. Sample vibrato uses a table 256-bytes long Note: The sample load routine uses bytes the at 2Eh and 2Fh for conversion flags! So DON'T write anything there! All samples are UNSIGNED (even 16-bit ones) Impulse Pattern Format 0 1 2 3 4 5 6 7 8 9 A B C D E F ┌───────┬───────┬───┬───┬───┬───┬───────────────────────────────┐ 0000: │Length │ Rows │ x │ x │ x │ x │ Packed data................ │ ├───┬───┼───┬───┼───┼───┼───┼───┼───┬───┬───┬───┬───┬───┬───┬───┤ Length: Length of packed pattern, not including the 8 byte header Note that the pattern + the 8 byte header will ALWAYS be less than 64k Rows: Number of rows in this pattern (Ranges from 32->200) Patterns are unpacked by the following pseudocode... GetNextChannelMarker: Read byte into channelvariable. if(channelvariable = 0) then end of row Channel = (channelvariable-1) & 63 ; Channel is 0 based. if(channelvariable & 128) then read byte into maskvariable else maskvariable = previousmaskvariable for current channel if(maskvariable & 1), then read note. (byte value) // Note ranges from 0->119 (C-0 -> B-9) // 255 = note off, 254 = notecut if(maskvariable & 2), then read instrument (byte value) // Instrument ranges from 1->99 // Internally, 0 is used for no instrument, but should // NEVER be found in a module... if(maskvariable & 4), then read volume/panning (byte value) // Volume ranges from 0->64 // Panning ranges from 0->64, mapped onto 128->192 if(maskvariable & 8), then read command (byte value) and commandvalue // Valid ranges from 0->31 (0=no effect, 1=A, 2=B, 3=C, etc.) if(maskvariable & 16), then note = lastnote for channel if(maskvariable & 32), then instrument = lastinstrument for channel if(maskvariable & 64), then volume/pan = lastvolume/pan for channel if(maskvariable & 128), then { command = lastcommand for channel and commandvalue = lastcommandvalue for channel } Goto GetNextChannelMarker Mathematics Abbreviations: FV = Final Volume (Ranges from 0 to 128). In versions 1.04+, mixed output devices are reduced further to a range from 0 to 64 due to lack of memory. Vol = Volume at which note is to be played. (Ranges from 0 to 64) SV = Sample Volume (Ranges from 0 to 64) CV = Channel Volume (Ranges from 0 to 64) GV = Global Volume (Ranges from 0 to 128) VEV = Volume Envelope Value (Ranges from 0 to 64) In Sample mode, the following calculation is done: FV = Vol * SV * CV * GV / 262144 ; Note that 262144 = 2^18 ; So bit shifting can be done. In Instrument mode the following procedure is used: 1) Update volume envelope value. Check for loops / end of envelope. 2) If end of volume envelope (ie. position >= 200 or VEV = 0FFh), then turn on note fade. 3) If notefade is on, then NoteFadeComponent (NFC) = NFC - FadeOut ; NFC should be initialised to 512 when a note is played. 4) FV = Vol * SV * CV * GV * VEV * NFC / 8589934592 ; Note that 8589934592 = 2^33 Linear slides work like this: Final frequency = Original frequency * 2^(SlideValue/768) (I used a lookup table for the multipliers here) For command Exx, SlideValue = -4*EffectValue For command EEx, SlideValue = -EffectValue For command Fxx, SlideValue = 4*EffectValue For command FEx, SlideValue = EffectValue Note that sample vibrato always uses Linear slides. Notes about effects (as compared to other module formats) C This is now in *HEX*. (Used to be in decimal in ST3) E/F/G/H/U You need to check whether the song uses Amiga/Linear slides. H Vibrato in Impulse Tracker is two times finer than in any other tracker and is updated EVERY tick. E/F/G These commands ALL share the same memory. Yxy This uses a table 4 times larger (hence 4 times slower) than vibrato or tremelo. If the waveform is set to random, then the 'speed' part of the command is interpreted as a delay. If you read through this document and there are ANY points which you have troubles with (and have to try out), then let me know - because someone else will have the same questions - and I'd like to make this DOC as easy to understand as possible. General Info The player in Impulse Tracker 'allocates' channels to notes whenever they are *PLAYED*. In sample mode, the allocation is simple: Virtual Channel = 'Host' channel In instrument mode, the following procedure is used: Check if channel is already playing ---Yes--> set 'background' flag on. | 'Trigger' NNA. If NNA=cut, No then use this virtual | channel. | | |<------------------ else -----------------/ | v Search and find the first non-active virtual channel. | Non-active channel found? ----Yes----> Use this for playback. | No | v Search through and find the channel of lowest volume that is in the 'background' (ie. no longer controlled directly) | Background channel found? ----Yes----> Use this for playback. | No | v Return error - the note is *NOT* allocated a channel, and hence is not played. Actually, this is quite a simple process... just that it's another of those 'hassles' to have to write...