HERAD

HERAD System
Developer:	Rémi Herbulot
Header:	Custom
Content:	Notational
Instruments:	Optional
Target Output
Released:	1992-??-??
First Game:	Dune (DOS)
Extensions	*.agd *.sdb *.m32 *.ha2 *.hsq *.sqx *.sqz *.scd

Herbulot AdLib (HERAD) System is a music driver written by Rémi Herbulot, one of Cryo Interactive Entertainment co-founders and lead programmers. Stéphane Picq, Cryo's first music composer also helped design HERAD with Herbulot.

There are two major versions of the x86 music driver that are known to exist; the second version is exclusive to the DOS port of MegaRace. HERAD was also ported to the Z80 for Cryo's two Sega CD titles.

Stéphane Picq had this to say about HERAD:

“

I designed HERAD because the existing softwares [sic] didn't take advantages of all sound parameters, and were very poor in expressiveness, the only dynamic being volume of notes. Basically, in HERAD several individual parameters of the soundpatches (like volume of operators) can be modulated individually, by velocity, modulation wheel, or aftertouch, like a real synth. Also, we used some "hidden" parameters not documented by Adlib, but mentioned in the Yamaha technical notice of the chip FM YM3812.

„

Dune (the first game to utilize HERAD) lists in the credit roll a special thanks to "Henri Chalifour and Grant Hamilton from the Ad Lib Company", who also were involved in the development of the music format.

Henri Chalifour said this in regards to HERAD development on Dune:

“

Regarding my involvement with Cryo Interactive, as far as I remember I shared with Mr. Picq some tricks, recipes and advices [sic] concerning sound designing. Being quite comfortable within the Ad Lib environment, It was however a modest contribution that I brought.

„

HERAD was used in only three games and all of the music was written by Picq. These games are: Dune, KGB aka Conspiracy, and MegaRace. All three games have been arguably rated as some of the best DOS game soundtracks ever written for OPL2.

While the final version of Lost Eden (DOS) does not use HERAD, a rare non-interactive demo of the game from Spring 1994 actually reuses the earlier HERAD driver from Dune. According to Stéphane Picq, the development team hadn't completely decided if they wanted streaming audio or sequenced FM music for the game, so for this early demo an Adlib version of the track "Citadel" is used.

Before the file format was reverse-engineered in 2016, Picq was the only composer who had written music for HERAD.

Players

(Category)

• RdosPlay - DOS - only version 1 (OPL2/OPL3 music)
• MGRCPLAY - DOS - only version 2 (requires DFADL.HSQ driver)

Converters

(Category)

HERAD to ?

• MIDIPLEX - Windows - MIDI

Games

(Category)

Released	Title	Sample
1992-??-??	Dune (DOS)
1992-??-??	KGB (DOS)
1993-??-??	Dune (SCD)
1993-??-??	MegaRace (DOS)
1994-??-??	MegaRace (SCD)
1994-??-??	Lost Eden (DOS) (Non-interactive demo only)

Technical Specifiations

File Formats

HERAD comes in several different file formats. The data is usually packed inside HSQ or SQX files.

• HSQ are compressed files with the Herbulot Sequencer algorithm, which is similar to LZ** dictionary algorithms. HSQ files can be found in Dune and MegaRace.
• SQX is another compression format, that seems to be similar to HSQ, but decompression is currently not possible except for playback in RDOSPlay.
• In the non-interactive demo for Dune, the music files are compressed in a format called SQZ, however, these files are identical to HSQ files.

Once the data is decompressed, there are several different file extensions that are used. Since HSQ doesn't keep the original data's filename or extention, it is assumed that these file extentions are retronyms and were given to the raw data after they were decompressed.

• The file extensions stand for different sound devices:
  • SDB - AdLib/Sound Blaster (OPL2)
  • AGD - AdLib Gold 1000 (OPL3)
  • M32 - Roland MT-32 (LA32)
  • SCD - Sega CD (OPN2)

Since the DOS port of MegaRace uses version 2, loading any of the game's music files into RDOSPlay will not work as the NoteOff MIDI events are different. It has been proposed that HERAD version 2 music files should use the file extension HA2 (HERAD version 2) instead of SDB to avoid errors.

Musical Notation

• The internal music notation is very similar to MIDI, however Pitch Bend and Meta events do differ.
• M32 and SCD files usually contain one multi-channel track, while SDB/AGD files may contain multiple tracks.
• Drivers that take music files with a single track utilize channel numbers as in MIDI, and typically dynamically allocate hardware channels. Drivers that take multiple tracks statically allocate one hardware channel to each track and consequently ignore channel numbers and their music files by convention use the first channel (0/1) for all events.

Speech Synthesis

As heard in the KGB song, "Gorbi", the word "Gorbachev" is played around 1:00. It was assumed that speech synthesis or perhaps PCM audio was possible with HERAD; however, after analyzing the uncompressed music file, it turns out the speech synthesis is just very clever MIDI sequencing and OPL2 programming done by Stéphane Picq to produce pseudo-speech synthesis.

Version Compatibility

Since HERAD version 2 was used exclusively in MegaRace (DOS), this means HERAD Version 1 was used in Dune, KGB, the Sega/Mega CD version of MegaRace, and the non-interactive demo of Lost Eden.

MegaRace's driver differs from the earlier Dune version with the introduction of a drum map mode that makes it much easier to sequence one-shot percussion instruments. In order to save on memory, the MIDI NoteOff events are truncated, which prevents MegaRace's music files from playing correctly with Dune or KGB's music driver.

Unfortunately, the header found inside HERAD music files do not provide any info on which version is being used. In order to detect the proper version, each music file needs to be inspected. For version 2 files, checking for truncated NoteOff events or a drum map inside the instrument chunk should work. The quickest and easiest way though would be to use a different file extension altogether (like HA2 mentioned earlier).

File structure

There are three chunks to HERAD files: the header, the MIDI data, and the Instrument chunk. Note that the Instrument chunk is absent in M32 files.

Header

All values in the header are in little endian format. For M32 files, the wFileSize value represents the total file size, while for others it represents the offset of the instrument chunk.

Data type	Name	Description
UINT16	wFileSize	Size of uncompressed file / Instrument Chunk offset
UINT16[21]	wOffsets	Array of relative offsets to the MIDI tracks (0 = track doesn't exist)
UINT16	wLoopStart	Loop starts at this measure (0 = don't loop)
UINT16	wLoopEnd	Loop ends at this measure (0 = don't loop)
UINT16	wLoopCount	Number of times the selected measures will play (0 = loop forever; >0 - play N times)
UINT16	wSpeed	Fixed point value that controls music speed. Value range is 0x0100 - 0x8100
UINT8[32]	bGoldRegs	Register values for AdLib Gold 1000 surround module. Only found in AGD files Modifying these values produces no changes to regular OPL3 playback

Looping

Looping a song works by specifying the start and end points with the wLoopStart and wLoopEnd bytes, and denoting how many times the loop should play with the wLoopCount byte. This can be used to either play a song forever, or to play a song that doesn't repeat but has a short segment that loops instead (like a repeating melody or phrase). For example, to loop the first two measures of the song, the wLoopStart byte will be 01 and the wLoopEnd byte will be 03. A measure is 96 MIDI ticks in duration.

For version 1 songs, in order for music to repeat, this loop data must be in place, though this appears to be a property of the driver or game, as MegaRace (SCD) uses version 1 and automatically loops. Version 2 songs that are being played back in MegaRace's sound engine will automatically repeat forever even if the wLoopCount field specifies that the song should only be played once. If there are no loop points in the file, the version 2 song will automatically repeat from beginning to end. As a result, several tracks in MegaRace (NewSan, Maeva and Terminal City) have short loops that are only a few measures long. Because those loop points are being used, the music continues to loop the song from beginning to end due to the sound engine. The other remaining tracks from MegaRace (Factory Land, Skyholder and Fractalian Space) have intros to them that are not repeated so their loop points start at the end of the intro and finish when the song is over.

Speed / Tempo

The default tempo is 500 BPM with the MIDI data at 24 ticks per quarter note. Obviously, this default value is way too fast so to slow down the music, a fixed-point value must be entered into the wSpeed field. To calculate the tempo of the song, take 500 and divide it by the value. Since this is a fixed-point number, some BPM will be at odd values. HERAD driver refresh rate is around 200.299 Hz. You can calculate ticks per second frequency by dividing refresh rate by the speed value.

Some of these values were taken from MegaRace and Dune files.

Speed value	Fixed-Point value	Approximate BPM	Frequency (Hz)
0x0100	1.0	500	= 200.299
0x03E0	3.875	129.032	≈ 51.69
0x0400	4.0	125	≈ 50.07
0x042B	4.168	119.961	≈ 48.06
0x04B8	4.71875	105.960	≈ 42.45
0x0500	5	100	≈ 40.06

AdLib Gold Settings

In AGD files, there's an additional chunk of 32 bytes in the header before the MIDI notation begins. These bytes are register values for various settings on the rare AdLib Gold 1000 sound card.

Offset	Description	Notes
0x0	TDA8425 register value (Gold control register 8)	0xD6 = pseudo stereo; 0xDE = spatial stereo. Since this seems to be the register value for the TDA8425 chip, other values should be valid (in theory). Dune only uses 0xD6 or 0xDE. According to the TDA8425 datasheet, spatial stereo is for handling stereo sound and pseudo stereo is for mono sound.
0x1-0x1F	YM7128 (Surround Module) register values	These are the raw register values for the YM7128 chip that is found on the Surround Module of the AdLib Gold 1000. The YM7128 creates the reverb and delay signal processing that the AdLib Gold 1000 is known for.

Only two songs (MORNING and WORMSUIT) use the spatial stereo setting for the TDA8425.

MIDI notation

• Most of the status bytes are compatible with the MIDI standard.
• It looks like running status is not supported as all known songs programmed in HERAD never use it.
• All MIDI data for Cryo's games uses 24 ticks per quarter note.

MIDI message	Description	MIDI compatible
8# xx xx	Note Off (version 1)	Yes
8# xx	Note Off (version 2)	No
9# xx xx	Note On	Yes
A# ?? ??	Poly Aftertouch (unused)	Unknown
B# xx xx	Control Change (M32)	Yes
C# xx	Program Change (uses internal instruments except for M32)	Yes
D# xx	Channel Aftertouch (only version 1)	Yes
E# xx	Pitch Bend (non-M32)	No
E# xx xx	Pitch Bend (M32)	Yes
FF	Track End

Note Off

For the Note Off command in version 2 songs, the velocity byte has been removed. Some older MIDI sequencers back in the '80s and early '90s did this to stop sending redundant data.

Pitch Bend

There are a few critical distinctions between HERAD's PitchBend and MIDI's PitchWheel events. First and foremost, MIDI's PitchWheel is persistent, continuing beyond the end of any note and applying to new notes on the channel until it is changed. In contrast, HERAD's PitchBend applies only to the single note currently playing on the channel and is reset to center (no bend) on the next NoteOn event.

In non-M32 files Pitch Bend command has only the MSB byte available. Like the MIDI Standard dictates, 0x40 is the "center" of the pitch bend range. Sending this 0x40 data byte after the Pitch Bend status byte will result in no change to the pitch. This event does differ from it's MIDI counterpart since the value range for Pitch Bend is 0x00 to 0x80, which surpasses MIDI's 7-bit value range. 0x00 equals to 2 semitones down and 0x80 equals to 2 semitones up.

The frequency number range for pitch bends is 325 to 685. For example, if the sequencer were to play a 2 semitone pitch bend downwards from C to A#, it would start at FNum 343, go down to 325 and then decrease the block number and continue the pitch bend at 650 (B, which is 1 semitone down from C) and finally stopping at 614 aka A sharp. If a 2 semitone pitch bend upwards were to happen at B, the FNum will start at 650, continue to increment the FNum until it reaches 685. Once there, it goes to the next block number and resumes increasing the FNum starting at 343 (which is C) before finishing the pitch bend 2 semitones up at 364 (which is C sharp).

Because the pitch bend event has a full 8-bit value instead of MIDI's standard 7-bit value, it is possible to go up higher above 0x80. For example, a pitch bend value of 0xFF when played on a C note will bend the pitch all the way up to F#, a 6 semitone difference.

Channel Aftertouch

Dune uses Aftertouch events to control the velocity of sustaining notes, as heard in the song, "Morning". However, HERAD 2 drops support of Aftertouch completely. Songs that have Aftertouch events will still play but the aftertouch events will be ignored. In the MegaRace music files, Channel Aftertouch only occurs one time in one song (Fractalian Space).

Note Pitch / Frequency Number Table

HERAD uses MIDI Notes C1 to B8 (0x18 to 0x77). If any MIDI notes are out of range, the sequencer will play note C1. The Block number corresponds with the MIDI octave (Block number 0 = MIDI octave 1, Block number 1 = MIDI octave 2, etc).

MIDI Note	F-Num
C	343
C#	364
D	385
D#	408
E	433
F	459
F#	486
G	515
G#	546
A	579
A#	614
B	650

Instrument Data

The instrument chunk contains all the sound chip register values needed for each instrument, along with some macros that control various parameters of the instrument during playback. Each instrument is 0x28 bytes long for the OPL, 0x2E bytes for the OPN. Version 2 of HERAD introduced a keymap instrument that can be used for linking several instruments into one; this allows for some very complex drum sequencing.

To use an instrument, the MIDI notation must use the "Program Change" message and specify a number for the instrument to be used. All instruments are listed sequentially and the first instrument is always number #0. Let's say we want to play the 13th instrument in the chunk. We tell the MIDI data to Program Change to instrument number #12 (C0 0C) and the notation after that will play using that instrument until the end of the track or another Program Change message is sent.

It seems that the OPL register values are almost in the exact same layout as the BNK format (technical). Thanks to Malvineous for his documentation on the BNK file format.

These offsets are still a work in progress and need more research.

OPL Instruments

Offset	Size	Name	Description	OPL base register	Notes
0x0	1		Mode		Denotes if this is an instrument or a version 2 keymap. Normally 0x0 in version 1 songs; either 0x1 or 0xFF in version 2 songs As long as this value is not set to 0xFF in a version 2 song, this can be set to any number.
0x1	1		Voice number		Most likely a meta identifier (changing this value has no effect in any song)
0x2	1	ksl	Modulator Key scaling level	0x40 (bits 6-7)
0x3	1	multiple	Modulator Frequency multiplier	0x20 (bits 0-3)
0x4	1	feedback	Feedback	0xC0 (bits 1-3)
0x5	1	attack	Modulator Attack	0x60 (upper four bits)
0x6	1	sustain	Modulator Sustain	0x80 (upper four bits)
0x7	1	eg	Modulator Envelope gain	0x20 (bit 5)	nonzero value is on
0x8	1	decay	Modulator Decay	0x60 (lower four bits)
0x9	1	releaseRate	Modulator Release	0x80 (lower four bits)
0xA	1	totalLevel	Modulator Output Level	0x40 (bit 0-5)	Output level is NOT affected by MIDI Velocity. To enable velocity, see offset 0x1E
0xB	1	am	Modulator Amplitude modulation (Tremolo)	0x20 (bit 7)
0xC	1	vib	Modulator Frequency Vibrato	0x20 (bit 6)
0xD	1	ksr	Modulator Key scaling/envelope rate	0x20 (bit 4)
0xE	1	con	Connector	0xC0 (bit 0, inverted)	0: OPL bit set to 1 other: OPL bit set to 0
0xF	1	ksl	Carrier Key scaling level	0x40 (bits 6-7)
0x10	1	multiple	Carrier Frequency multiplier	0x20 (bits 0-3)
0x11	1		Panning (OPL3)	0xC0 (upper four bits)	This controls the upper bits of the 0xC0 register to control panning in OPL3. 3 = both speakers; 2 = right speaker; 1 = left speaker MegaRace uses 3 as the default value. Dune's OPL2 driver ignores this byte and sets it to 0. Dune's OPL3 driver defaults any invaild value to both speakers.
0x12	1	attack	Carrier Attack	0x60 (upper four bits)
0x13	1	sustain	Carrier Sustain	0x80 (upper four bits)
0x14	1	eg	Carrier Envelope gain	0x20 (bit 5)	nonzero value is on
0x15	1	decay	Carrier Decay	0x60 (lower four bits)
0x16	1	releaseRate	Carrier Release	0x80 (lower four bits)
0x17	1	totalLevel	Carrier Output Level	0x40 (bit 0-5)	Output level is NOT affected by MIDI Velocity. To enable velocity, see offset 0x1F
0x18	1	am	Carrier Amplitude modulation (Tremolo)	0x20 (bit 7)
0x19	1	vib	Carrier Frequency Vibrato	0x20 (bit 6)
0x1A	1	ksr	Carrier Key scaling/envelope rate	0x20 (bit 4)
0x1B	1	HERAD Macro	Feedback Scaling - Aftertouch	0xC0 (bits 1-3)	This modifies feedback based off of MIDI Aftertouch events. Value range goes from 1-6 and FF-FA; 0 turns the scaling off. If Feedback (0x4) has already been assigned, that value will be added to the scaling.
0x1C	1		Modulator Waveform Select	0xE0 (bits 0-1)	Bits 0-2 for AGD
0x1D	1		Carrier Waveform Select	0xE0 (bits 0-1)	Bits 0-2 for AGD
0x1E	1	HERAD Macro	Modulator Output Level Scaling	0x40 (bit 0-5)	This uses the MIDI NoteOn velocity to control the Modulator Output level Value range goes from 1-4 and FF-FC; 0 turns the scaling off. Due to the design of the OPL2 chip, the higher values will decrease the volume and vice versa.
0x1F	1	HERAD Macro	Carrier Output Level Scaling	0x40 (bit 0-5)	Same as previous macro, only this affects the Carrier operator. Seems to multiply the velocity value; as a result some notes that are too loud or quiet will not be affected since the sum will be out of range for the OPL chip.
0x20	1	HERAD Macro	Feedback Scaling - Velocity	0xC0 (bits 1-3)	Same concept as the previous two macros, however this modifies feedback based off of MIDI NoteOn velocity. Value range goes from 1-6 and FF-FA; 0 turns the scaling off. If Feedback (0x4) has already been assigned, that value will be added to the scaling.
0x21	1	HERAD Macro	Pitch Slide Range Flag		Increases pitch bend range (Fine tune = 0, Coarse tune = 1)
0x22	1	HERAD Macro	Root Note Transpose		Normally set at 0x0 and accepts signed integers, for example, 0xC = an octave higher; 0xF4 = an octave lower This macro functions very differently in HERAD version 2, see Root Note Macro
0x23	1	HERAD Macro	Pitch Slide Duration		Duration of the pitch bend in ticks
0x24	1	HERAD Macro	Pitch Slide Range		Signed integer value. For each MIDI tick, increase or decrease the FNUM by 1 when fine tune is on. When coarse tune is on, a 60-note scale is used (see Coarse Pitch Slide Frequency Table).
0x25	1	Unknown	Unused		While this byte is used in some instruments for Dune, KGB, and MegaRace, extensive testing shows that this byte doesn't change any OPL registers or affect playback at all. This byte is considered unused.
0x26	1	HERAD Macro	Modulator Output Level Aftertouch Scaling		This uses the MIDI Channel Aftertouch events to modify the modulator output level. Just like in 0x1E, the value range goes from 1-4 and FF-FC; 0 turns the scaling off. For some reason, in version 2 instruments, this is always set to 0x1
0x27	1	HERAD Macro	Carrier Output Level Aftertouch Scaling		This uses the MIDI Channel Aftertouch events to modify the carrier output level. Just like in 0x1F, the value range goes from 1-4 and FF-FC; 0 turns the scaling off. In MegaRace, this is always set to zero. In order for this macro to function, the 0x1F byte MUST be enabled.

OPN Instruments

Only version 1 was ever implemented on the OPN.

For brevity, only values and details which do not directly correspond to the contents of the relevant registers (e.g. which bits are used, or whether the value's effect is positive or negative) are described. See the Genesis Technical Overview or PlutieDev's YM2612 reference for any information that may have been omitted.

For per-operator and operator mask values, little-endian order is consistently used i.e. the low bit or first byte corresponds to operator 1.

Offset	Size	Name	Description	OPN base register	Notes
0x0	1		Generic Operator Levels Mask		Specifies which operators should have their Base Operator Level assigned at patch change application (typically in the first NoteOn event after a patch change). Bits 4-7 contain a bit mask of operators (bit 4 corresponds to operator 1, bit 7 corresponds to operator 4). If the corresponding bit is set, the Base Operator Level is set; if the bit is clear, the operator's total left is cleared to $7f (minimum amplitude). See Base Operator Level for further explanation.
0x1-0x4	1	DT1-MUL	Operator Detuning and Frequency Multiplier	0x3x	Directly copied into the OPN DT1-MUL registers. The high bit of the first byte (unused by the OPN) appears to be a flag of some kind but its function is not apparent.
0x5-0x8	1	TL	Base Operator Level	0x4x	Base total level (e.g. volume) for the operator, prior to any modification for e.g. velocity. If bit 7 is set the operator ignores global volume, but may still be modified by velocity and aftertouch. The operator total level is applied to the OPN in four places, and velocity, aftertouch, and global volume modifications all stack. At patch change application, it will be applied as specified under Generic Operator Levels Mask. If the operator is sensitive to velocity, it will be set during the NoteOn event, overwriting the value set at patch change. If the operator is sensitive to aftertouch, it will be set in ChannelAftertouch events. Finally, if the operator is sensitive to global volume, global volume commands from the game will set the total level.
0x9-0xC	1	RS-AR	Operator Rate Scaling and Attack Rate	0x5x	Directly copied to the OPN RS-AR register.
0xD-0x10	1	AM-D1R	Amplitude Modulation and Decay Rate	0x6x	Directly copied to the OPN AM-D1R register.
0x11-0x14	1	D2R	Sustain Rate	0x7x	The rate of decay during the sustain envelope phase, for instruments that cannot indefinitely sustain notes e.g. piano. Directly copied to the OPN D2R register.
0x15-0x18	1	D1L-RR	Decay Level and Release Rate	0x8x	Directly copied to the OPN D1L-RR register.
0x19-0x1C	1	SSG-EG	Envelope Shape	0x9x	Directly copied to the OPN SSG-EG register. See https://www.plutiedev.com/ym2612-registers#reg-90.
0x1D	1	FB-ALG	Feedback and FM Algorithm	0xB0-B3	Operator 1 feedback level prior to modification by velocity and/or aftertouch, and operator connectivity "algorithm".
0x1E	1	LR-MS	Stereo Selection and LFO Modulation Sensitivity	0xB4-0xB7	Directly copied to the OPN LR-MS register.
0x1F-0x22	1	HERAD Macro	Operator Level Velocity Sensitivity	0x4x	The sensitivity of the given operator's total level to the velocity of the NoteOn event. This value ranges from -4 to +4, and if non-zero the following equation is applied: total level += (sensitivity > 0 ? velocity : 0x80 - velocity) >> (4 - abs(sensitivity)).
0x23-0x26	1	HERAD Macro	Operator Level Aftertouch Sensitivity	0x4x	The sensitivity of the given operator's total level to the velocity of the ChannelAftertouch event. This value ranges from -4 to +4, and if non-zero the following equation is applied: total level += (sensitivity > 0 ? velocity : 0x80 - velocity) >> (4 - abs(sensitivity)).
0x27	1	HERAD Macro	Feedback Velocity Sensitivity	0xB0-B3	The sensitivity of operator 1's feedback strength to the velocity of the NoteOn event. This value ranges from -6 to +6, and if non-zero the following equation is applied: feedback += (sensitivity > 0 ? velocity : 0x80 - velocity) >> (6 - abs(sensitivity)).
0x28	1	HERAD Macro	Pitch Bend Range		Determines how note frequency is affected by pitch bends and slides. Note that a bug in the coarse tuning code breaks partial-note bends (a lookup into a partial pitch table is made, but the value is immediately overwritten in its register before it can be applied to the frequency). If 0: fine tuning: key += (bend value - 0x40) / 0x20, frequency = key frequency * (1.0 + ((bend value - 0x40) % 0x20) / 32.0) If non-zero: coarse tuning: key += (bend value - 0x40) / 5, frequency = key frequency + (bend value - 0x40) % 5
0x29	1	HERAD Macro	Fundamental Frequency Key Offset		Added to the key number to compute the fundamental frequency to use to program the OPN.
0x2A	1	HERAD Macro	Pitch Slide Duration		Duration of the pitch slide in ticks. If 0, pitch slide is not used.
0x2B	1	HERAD Macro	Pitch Slide Rate		This value is added to the current pitch bend value every tick, which is applied to the currently playing note by the normal equations.
0x2C	1	LFO	LFO Frequency	0x22	If bit 3 is clear, bit 3 is set (enabling LFO) and this value is copied to the LFO register when a patch change is applied. As there is a single global LFO for the OPN, it is only feasible for all simultaneously used instruments that have bit 3 clear to have the same LFO frequency. This field is 0 (enable LFO and set to 3.98 Hz) in all observed instruments.
0x2D	1	HERAD Macro	Feedback Aftertouch Sensitivity		The sensitivity of operator 1's feedback strength to the velocity of ChannelAftertouch events. This value ranges from -6 to +6, and if non-zero the following equation is applied: feedback += (sensitivity > 0 ? aftertouch : 0x80 - aftertouch) >> (6 - abs(sensitivity)).

Coarse Pitch Slide Frequency Table

When the Pitch Slide Range Flag (0x21) is set to the coarse tune setting, 4 additional F-Nums are added to each note of the standard 12-note scale, resulting in a 60-note scale. The sequencer will cycle through all the F-Nums until the next Note Off or the pitch slide exceeds the MIDI Note Range or until the end of the Pitch Slide Duration (0x23).

MIDI Note and Corresponding F-Num		Additional F-Nums added to 12 note scale
C	343	348	353	358	363
C#	364	369	374	379	384
D	385	390	395	400	405
D#	408	413	418	423	428
E	433	438	443	448	453
F	459	464	469	474	479
F#	486	492	498	504	510
G	515	521	527	533	539
G#	546	552	558	564	570
A	579	585	591	597	603
A#	614	620	626	632	638
B	650	656	662	668	674

Output Level Scaling Table

The following is the lookup table for the output level scaling macros. 3F is the quietest output level whereas 00 is the loudest. If any of the output level values (0xA and 0x17) have already been assigned, that value will be added to the scaling.

MIDI Velocity	4	3	2	1	FF	FE	FD	FC
0	3F	3F	20	10	0	0	0	0
1	3F	3F	1F	0F	0	0	0	1
2	3F	3F	1F	0F	0	0	1	2
3	3F	3E	1F	0F	0	0	1	3
4	3F	3E	1F	0F	0	1	2	4
5	3F	3D	1E	0F	0	1	2	5
6	3F	3D	1E	0F	0	1	3	6
7	3F	3C	1E	0F	0	1	3	7
8	3F	3C	1E	0E	1	2	4	8
9	3F	3B	1D	0E	1	2	4	9
0A	3F	3B	1D	0E	1	2	5	0A
0B	3F	3A	1D	0E	1	2	5	0B
0C	3F	3A	1D	0E	1	3	6	0C
0D	3F	39	1C	0E	1	3	6	0D
0E	3F	39	1C	0E	1	3	7	0E
0F	3F	38	1C	0E	1	3	7	0F
10	3F	38	1C	0D	2	4	8	10
11	3F	37	1B	0D	2	4	8	11
12	3F	37	1B	0D	2	4	9	12
13	3F	36	1B	0D	2	4	9	13
14	3F	36	1B	0D	2	5	0A	14
15	3F	35	1A	0D	2	5	0A	15
16	3F	35	1A	0D	2	5	0B	16
17	3F	34	1A	0D	2	5	0B	17
18	3F	34	1A	0C	3	6	0C	18
19	3F	33	19	0C	3	6	0C	19
1A	3F	33	19	0C	3	6	0D	1A
1B	3F	32	19	0C	3	6	0D	1B
1C	3F	32	19	0C	3	7	0E	1C
1D	3F	31	18	0C	3	7	0E	1D
1E	3F	31	18	0C	3	7	0F	1E
1F	3F	30	18	0C	3	7	0F	1F
20	3F	30	18	0B	4	8	10	20
21	3F	2F	17	0B	4	8	10	21
22	3F	2F	17	0B	4	8	11	22
23	3F	2E	17	0B	4	8	11	23
24	3F	2E	17	0B	4	9	12	24
25	3F	2D	16	0B	4	9	12	25
26	3F	2D	16	0B	4	9	13	26
27	3F	2C	16	0B	4	9	13	27
28	3F	2C	16	0A	5	0A	14	28
29	3F	2B	15	0A	5	0A	14	29
2A	3F	2B	15	0A	5	0A	15	2A
2B	3F	2A	15	0A	5	0A	15	2B
2C	3F	2A	15	0A	5	0B	16	2C
2D	3F	29	14	0A	5	0B	16	2D
2E	3F	29	14	0A	5	0B	17	2E
2F	3F	28	14	0A	5	0B	17	2F
30	3F	28	14	9	6	0C	18	30
31	3F	27	13	9	6	0C	18	31
32	3F	27	13	9	6	0C	19	32
33	3F	26	13	9	6	0C	19	33
34	3F	26	13	9	6	0D	1A	34
35	3F	25	12	9	6	0D	1A	35
36	3F	25	12	9	6	0D	1B	36
37	3F	24	12	9	6	0D	1B	37
38	3F	24	12	8	7	0E	1C	38
39	3F	23	11	8	7	0E	1C	39
3A	3F	23	11	8	7	0E	1D	3A
3B	3F	22	11	8	7	0E	1D	3B
3C	3F	22	11	8	7	0F	1E	3C
3D	3F	21	10	8	7	0F	1E	3D
3E	3F	21	10	8	7	0F	1F	3E
3F	3F	20	10	8	7	0F	1F	3F
40	3F	20	10	7	7	10	20	3F
41	3F	1F	0F	7	8	10	20	3F
42	3E	1F	0F	7	8	10	21	3F
43	3D	1E	0F	7	8	10	21	3F
44	3C	1E	0F	7	8	11	22	3F
45	3B	1D	0E	7	8	11	22	3F
46	3A	1D	0E	7	8	11	23	3F
47	39	1C	0E	7	8	11	23	3F
48	38	1C	0E	7	8	12	24	3F
49	37	1B	0D	6	9	12	24	3F
4A	36	1B	0D	6	9	12	25	3F
4B	35	1A	0D	6	9	12	25	3F
4C	34	1A	0D	6	9	13	26	3F
4D	33	19	0C	6	9	13	26	3F
4E	32	19	0C	6	9	13	27	3F
4F	31	18	0C	6	9	13	27	3F
50	30	18	0C	6	9	14	28	3F
51	2F	17	0B	5	0A	14	28	3F
52	2E	17	0B	5	0A	14	29	3F
53	2D	16	0B	5	0A	14	29	3F
54	2C	16	0B	5	0A	15	2A	3F
55	2B	15	0A	5	0A	15	2A	3F
56	2A	15	0A	5	0A	15	2B	3F
57	29	14	0A	5	0A	15	2B	3F
58	28	14	0A	5	0A	16	2C	3F
59	27	13	9	4	0B	16	2C	3F
5A	26	13	9	4	0B	16	2D	3F
5B	25	12	9	4	0B	16	2D	3F
5C	24	12	9	4	0B	17	2E	3F
5D	23	11	8	4	0B	17	2E	3F
5E	22	11	8	4	0B	17	2F	3F
5F	21	10	8	4	0B	17	2F	3F
60	20	10	8	4	0B	18	30	3F
61	1F	0F	7	3	0C	18	30	3F
62	1E	0F	7	3	0C	18	31	3F
63	1D	0E	7	3	0C	18	31	3F
64	1C	0E	7	3	0C	19	32	3F
65	1B	0D	6	3	0C	19	32	3F
66	1A	0D	6	3	0C	19	33	3F
67	19	0C	6	3	0C	19	33	3F
68	18	0C	6	3	0C	1A	34	3F
69	17	0B	5	2	0D	1A	34	3F
6A	16	0B	5	2	0D	1A	35	3F
6B	15	0A	5	2	0D	1A	35	3F
6C	14	0A	5	2	0D	1B	36	3F
6D	13	9	4	2	0D	1B	36	3F
6E	12	9	4	2	0D	1B	37	3F
6F	11	8	4	2	0D	1B	37	3F
70	10	8	4	2	0D	1C	38	3F
71	0F	7	3	1	0E	1C	38	3F
72	0E	7	3	1	0E	1C	39	3F
73	0D	6	3	1	0E	1C	39	3F
74	0C	6	3	1	0E	1D	3A	3F
75	0B	5	2	1	0E	1D	3A	3F
76	0A	5	2	1	0E	1D	3B	3F
77	9	4	2	1	0E	1D	3B	3F
78	8	4	2	1	0E	1E	3C	3F
79	7	3	1	0	0F	1E	3C	3F
7A	6	3	1	0	0F	1E	3D	3F
7B	5	2	1	0	0F	1E	3D	3F
7C	4	2	1	0	0F	1F	3E	3F
7D	3	1	0	0	0F	1F	3E	3F
7E	2	1	0	0	0F	1F	3F	3F
7F	1	0	0	0	0F	1F	3F	3F

Feedback Scaling Table

The following is the lookup table for the feedback scaling macros. If the feedback value (0x4) has already been assigned, that value will be added to the scaling. The feedback value ranges from 0-7.

MIDI Velocity	6	5	4	3	2	1	FF	FE	FD	FC	FB	FA
0	7	7	7	7	4	2	0	0	0	0	0	0
1	7	7	7	7	3	1	0	0	0	0	0	0
2	7	7	7	7	3	1	0	0	0	0	0	1
3	7	7	7	7	3	1	0	0	0	0	0	1
4	7	7	7	7	3	1	0	0	0	0	1	2
5	7	7	7	7	3	1	0	0	0	0	1	2
6	7	7	7	7	3	1	0	0	0	0	1	3
7	7	7	7	7	3	1	0	0	0	0	1	3
8	7	7	7	7	3	1	0	0	0	1	2	4
9	7	7	7	7	3	1	0	0	0	1	2	4
0A	7	7	7	7	3	1	0	0	0	1	2	5
0B	7	7	7	7	3	1	0	0	0	1	2	5
0C	7	7	7	7	3	1	0	0	0	1	3	6
0D	7	7	7	7	3	1	0	0	0	1	3	6
0E	7	7	7	7	3	1	0	0	0	1	3	7
0F	7	7	7	7	3	1	0	0	0	1	3	7
10	7	7	7	7	3	1	0	0	1	2	4	7
11	7	7	7	6	3	1	0	0	1	2	4	7
12	7	7	7	6	3	1	0	0	1	2	4	7
13	7	7	7	6	3	1	0	0	1	2	4	7
14	7	7	7	6	3	1	0	0	1	2	5	7
15	7	7	7	6	3	1	0	0	1	2	5	7
16	7	7	7	6	3	1	0	0	1	2	5	7
17	7	7	7	6	3	1	0	0	1	2	5	7
18	7	7	7	6	3	1	0	0	1	3	6	7
19	7	7	7	6	3	1	0	0	1	3	6	7
1A	7	7	7	6	3	1	0	0	1	3	6	7
1B	7	7	7	6	3	1	0	0	1	3	6	7
1C	7	7	7	6	3	1	0	0	1	3	7	7
1D	7	7	7	6	3	1	0	0	1	3	7	7
1E	7	7	7	6	3	1	0	0	1	3	7	7
1F	7	7	7	6	3	1	0	0	1	3	7	7
20	7	7	7	6	3	1	0	1	2	4	7	7
21	7	7	7	5	2	1	0	1	2	4	7	7
22	7	7	7	5	2	1	0	1	2	4	7	7
23	7	7	7	5	2	1	0	1	2	4	7	7
24	7	7	7	5	2	1	0	1	2	4	7	7
25	7	7	7	5	2	1	0	1	2	4	7	7
26	7	7	7	5	2	1	0	1	2	4	7	7
27	7	7	7	5	2	1	0	1	2	4	7	7
28	7	7	7	5	2	1	0	1	2	5	7	7
29	7	7	7	5	2	1	0	1	2	5	7	7
2A	7	7	7	5	2	1	0	1	2	5	7	7
2B	7	7	7	5	2	1	0	1	2	5	7	7
2C	7	7	7	5	2	1	0	1	2	5	7	7
2D	7	7	7	5	2	1	0	1	2	5	7	7
2E	7	7	7	5	2	1	0	1	2	5	7	7
2F	7	7	7	5	2	1	0	1	2	5	7	7
30	7	7	7	5	2	1	0	1	3	6	7	7
31	7	7	7	4	2	1	0	1	3	6	7	7
32	7	7	7	4	2	1	0	1	3	6	7	7
33	7	7	7	4	2	1	0	1	3	6	7	7
34	7	7	7	4	2	1	0	1	3	6	7	7
35	7	7	7	4	2	1	0	1	3	6	7	7
36	7	7	7	4	2	1	0	1	3	6	7	7
37	7	7	7	4	2	1	0	1	3	6	7	7
38	7	7	7	4	2	1	0	1	3	7	7	7
39	7	7	7	4	2	1	0	1	3	7	7	7
3A	7	7	7	4	2	1	0	1	3	7	7	7
3B	7	7	7	4	2	1	0	1	3	7	7	7
3C	7	7	7	4	2	1	0	1	3	7	7	7
3D	7	7	7	4	2	1	0	1	3	7	7	7
3E	7	7	7	4	2	1	0	1	3	7	7	7
3F	7	7	7	4	2	1	0	1	3	7	7	7
40	7	7	7	4	2	1	1	2	4	7	7	7
41	7	7	7	3	1	0	1	2	4	7	7	7
42	7	7	7	3	1	0	1	2	4	7	7	7
43	7	7	7	3	1	0	1	2	4	7	7	7
44	7	7	7	3	1	0	1	2	4	7	7	7
45	7	7	7	3	1	0	1	2	4	7	7	7
46	7	7	7	3	1	0	1	2	4	7	7	7
47	7	7	7	3	1	0	1	2	4	7	7	7
48	7	7	7	3	1	0	1	2	4	7	7	7
49	7	7	7	3	1	0	1	2	4	7	7	7
4A	7	7	6	3	1	0	1	2	4	7	7	7
4B	7	7	6	3	1	0	1	2	4	7	7	7
4C	7	7	6	3	1	0	1	2	4	7	7	7
4D	7	7	6	3	1	0	1	2	4	7	7	7
4E	7	7	6	3	1	0	1	2	4	7	7	7
4F	7	7	6	3	1	0	1	2	4	7	7	7
50	7	7	6	3	1	0	1	2	5	7	7	7
51	7	7	6	2	1	0	1	2	5	7	7	7
52	7	7	5	2	1	0	1	2	5	7	7	7
53	7	7	5	2	1	0	1	2	5	7	7	7
54	7	7	5	2	1	0	1	2	5	7	7	7
55	7	7	5	2	1	0	1	2	5	7	7	7
56	7	7	5	2	1	0	1	2	5	7	7	7
57	7	7	5	2	1	0	1	2	5	7	7	7
58	7	7	5	2	1	0	1	2	5	7	7	7
59	7	7	5	2	1	0	1	2	5	7	7	7
5A	7	7	4	2	1	0	1	2	5	7	7	7
5B	7	7	4	2	1	0	1	2	5	7	7	7
5C	7	7	4	2	1	0	1	2	5	7	7	7
5D	7	7	4	2	1	0	1	2	5	7	7	7
5E	7	7	4	2	1	0	1	2	5	7	7	7
5F	7	7	4	2	1	0	1	2	5	7	7	7
60	7	7	4	2	1	0	1	3	6	7	7	7
61	7	7	4	1	0	0	1	3	6	7	7	7
62	7	7	3	1	0	0	1	3	6	7	7	7
63	7	7	3	1	0	0	1	3	6	7	7	7
64	7	7	3	1	0	0	1	3	6	7	7	7
65	7	6	3	1	0	0	1	3	6	7	7	7
66	7	6	3	1	0	0	1	3	6	7	7	7
67	7	6	3	1	0	0	1	3	6	7	7	7
68	7	6	3	1	0	0	1	3	6	7	7	7
69	7	5	3	1	0	0	1	3	6	7	7	7
6A	7	5	2	1	0	0	1	3	6	7	7	7
6B	7	5	2	1	0	0	1	3	6	7	7	7
6C	7	5	2	1	0	0	1	3	6	7	7	7
6D	7	4	2	1	0	0	1	3	6	7	7	7
6E	7	4	2	1	0	0	1	3	6	7	7	7
6F	7	4	2	1	0	0	1	3	6	7	7	7
70	7	4	2	1	0	0	1	3	7	7	7	7
71	7	3	2	0	0	0	1	3	7	7	7	7
72	7	3	1	0	0	0	1	3	7	7	7	7
73	6	3	1	0	0	0	1	3	7	7	7	7
74	6	3	1	0	0	0	1	3	7	7	7	7
75	5	2	1	0	0	0	1	3	7	7	7	7
76	5	2	1	0	0	0	1	3	7	7	7	7
77	4	2	1	0	0	0	1	3	7	7	7	7
78	4	2	1	0	0	0	1	3	7	7	7	7
79	3	1	1	0	0	0	1	3	7	7	7	7
7A	3	1	0	0	0	0	1	3	7	7	7	7
7B	2	1	0	0	0	0	1	3	7	7	7	7
7C	2	1	0	0	0	0	1	3	7	7	7	7
7D	1	0	0	0	0	0	1	3	7	7	7	7
7E	1	0	0	0	0	0	1	3	7	7	7	7
7F	0	0	0	0	0	0	1	3	7	7	7	7

Root Note Macro

In the instrument chunk, offset 0x22 controls the root note of an instrument relative to a MIDI note's pitch, so for example, if you have a drum sound that you want to play at a particular pitch or you need your bass to be played an octave lower, you can set this byte to the pitch you want and the sequencer will play the instrument accordingly.

In HERAD version 1, the MIDI sequencer will take any note that's thrown at it and change the pitch, so if the value is 1 and the MIDI note that's being played is C4, then the sequencer will play C#4. If the note that needs to be changed is out of range on the MIDI keyboard (C1 to B8), HERAD will just play note C1 instead.

HERAD version 2 introduces some very different functionality when it comes to handling the root note. From value ranges D1-FF to 01-30, the root note works exactly the same as version 1. However, from D0 to B9 and 31 to 90, the pitches cycle through again but this time, MIDI Note pitches are ignored, so any note that is triggered in the sequencer has it's pitch overridden by the root note value.

The value range 91-B8 produces the same functionality, except if a MIDI Control Change event occurs, no notes after it will be played until the song repeats. No known HERAD instruments use this value range so it's most likely that this behavior is a glitch and is not used.

Root Note Macro Value Range	Function
31 - 90	MIDI NoteOn Pitch is ignored, all notes that are triggered will play the root note's pitch. Note that 30 and 31 share the same pitch, the only difference is that 30 can still be affected by MIDI pitch and 31 has it's pitch locked.
01 - 30	Root note goes upward.
00	No change
FF - D1	Signed integer; Root note goes downward.
D0 - B9	Signed integer; MIDI NoteOn Pitch is ignored, all notes that are triggered will play the root note's pitch. Note that D0 and D1 share the same pitch, the only difference is that D0 can still be affected by MIDI pitch and D1 has it's pitch locked.
B8 - 91	Unused; does the same thing as the previous value range, except any MIDI Control Change events will cause no further notes to play until the song repeats.

Keymap

Introduced in version 2 songs, a keymap control was added into the instrument chunk. All 6 songs in MegaRace use this keymapping for their drum sequencing. Like the other separate instruments in this chunk, it is also 0x28 bytes long, but differs greatly from the other instruments since it doesn't contain any OPL register values.

It is essentially an array of instruments that are mapped to different MIDI notes. Instead of having to send a Program Change MIDI message every time a different drum instrument is used, this keymap greatly reduces the amount of MIDI messages being sent since all the drum sounds are located in one instrument.

Offset	Description	Notes
0x0	Mode	Must always be 0xFF; this denotes that this is a keymap
0x1	Voice Number	Most likely a meta identifier (so far, changing this value results in no effect)
0x2	Keymap Offset	Must always be 0x18; changing this will offset the instruments sounds. Leaving this at 0x18 will have the keymap start at MIDI pitch #48 (aka C4). Decreasing the value will start the keymap at a lower pitch. For example, if you change the value to 0x11, the keymap will start at MIDI pitch #41 (aka F3)
0x3	Unknown	So far, changing this value results in no effect to any instruments inside the keymap range. Some instruments outside the keymap range may be affected, but these aren't suppose to be heard anyway.
0x4	Instrument Array	C4 (All array values are the MIDI instrument number assigned to that particular MIDI note)
0x5	Instrument Array	C#4
0x6	Instrument Array	D4
0x7	Instrument Array	D#4
0x8	Instrument Array	E4
0x9	Instrument Array	F4
0xA	Instrument Array	F#4
0xB	Instrument Array	G4
0xC	Instrument Array	G#4
0xD	Instrument Array	A4
0xE	Instrument Array	A#4
0xF	Instrument Array	B4
0x10	Instrument Array	C5
0x11	Instrument Array	C#5
0x12	Instrument Array	D5
0x13	Instrument Array	D#5
0x14	Instrument Array	E5
0x15	Instrument Array	F5
0x16	Instrument Array	F#5
0x17	Instrument Array	G5
0x18	Instrument Array	G#5
0x19	Instrument Array	A5
0x1A	Instrument Array	A#5
0x1B	Instrument Array	B5
0x1C	Instrument Array	C6
0x1D	Instrument Array	C#6
0x1E	Instrument Array	D6
0x1F	Instrument Array	D#6
0x20	Instrument Array	E6
0x21	Instrument Array	F6
0x22	Instrument Array	F#6
0x23	Instrument Array	G6
0x24	Instrument Array	G#6
0x25	Instrument Array	A6
0x26	Instrument Array	A#6
0x27	Instrument Array	B6

The keymap starts at MIDI pitch #48 (aka C4) and continues with each consecutive pitch (48, 49, 50, ..., etc).

Sometimes in the instrument array, there will be an instrument that covers several MIDI pitches, instead of just a single instance (for example, a tom-tom drum that requires different pitches). This is done by specifying the instrument's number (i.e. 0x10) and then for every repeating instrument, the keymap instrument's number itself is referenced. For example, let's say our keymap instrument is number "0xC" and we want to repeat the instrument "0x10" 8 times. We do this like so: 10 0C 0C 0C 0C 0C 0C 0C. Sometimes, this doesn't work due to an unknown glitch (possibly to do with drums that are played very quickly - like the grace note between the kick and snare in MegaRace's "Skyholder"). Instead of referencing the keymap's instrument number, repeating the drum instrument number itself will also work and is a work around for this glitch.

Again, all instruments in the instrument chunk must be 0x28 bytes long, so when all the instruments in the array are specified, the remaining bytes are to be padded out by the keymap instrument number.

Links

• File:MegaRace - DOS - Credits.png - HERAD system is mentioned in the credits of MegaRace (DOS).
• mobygames.com/developer/sheet/view/developerId,1760/ - HERAD System mentioned on MobyGames.
• vogons.org/viewtopic.php?f=7&t=49813 - Discussion on VOGONS.
• github.com/adplug/adplug/issues/39 - Format support request in AdPlug repository.
• sourceforge.net/p/adplug/feature-requests/18/ - Format support request in old AdPlug repository.
• youtube.com/watch?v=Y7rpRQnktQs - Stéphane Picq comment on YouTube regarding Lost Eden's demo using HERAD