FXZ

A recreation of sfxr. Wish me luck! All credit for the synth goes to Dr. Petter, I just ported a port and wrote down a binary format :)

Goals

• An embeddable synthesizer in < 1kb js (minified and gzipped)
• A binary format for saving and loading effects in 100 bytes
• Synth implementations in common languages (C, C#, Java, Lua, etc.)

FXZ Binary Format Specification

FXZ data is 100 bytes long. All multi-byte numeric types are little endian.

Offset	Size	Type	Field	Range
0	3	ascii	Magic Number	'fxz'
3	1	uint8	version	1
4	1	uint8	wave shape	0-3
5	3	-	unused	0
8	4	float32	attack time	[ 0,1]
12	4	float32	sustain time	[ 0,1]
16	4	float32	sustain punch	[ 0,1]
20	4	float32	decay time	[ 0,1]
24	4	float32	start frequency	[ 0,1]
28	4	float32	frequency cutoff	[ 0,1]
32	4	float32	frequency slide	[-1,1]
36	4	float32	delta slide	[-1,1]
40	4	float32	vibrato depth	[ 0,1]
44	4	float32	vibrato speed	[ 0,1]
48	4	float32	arp amount	[-1,1]
52	4	float32	arp change speed	[ 0,1]
56	4	float32	Square duty	[ 0,1]
60	4	float32	Duty sweep	[-1,1]
64	4	float32	Repeat speed	[ 0,1]
68	4	float32	Flanger offset	[-1,1]
72	4	float32	Flanger sweep	[-1,1]
76	4	float32	LPF cutoff	[ 0,1]
80	4	float32	LPF cutoff sweep	[-1,1]
84	4	float32	LPF resonance	[ 0,1]
88	4	float32	HPF cutoff	[ 0,1]
92	4	float32	HPF cutoff sweep	[-1,1]
96	4	float32	Volume	[ 0,1]

Recommended MIME type application/fxz.

Recommended file extension .fxz.

FXX Binary Format Specification

FXX is an FXZ Pack. It can contain up to uint32max entries. The size of the pack is 8 + 116 * numberOfEntries bytes. It adds 16 byte identifiers to each entry so they can be named. If you want them nameless to save those bytes you can glob up fxz data, just smash them all together, I don't think it warrants a formal specification.

All multi-byte numeric types are little endian.

Offset	Size	Type	Field	Range
0	3	ascii	Magic Number	'fxx'
3	1	uint8	version	1
4	4	uint32	# of entries	0-4294967295
*	16	ascii	fxz entry name
*+16	100	fxz	fxz entry data	valid fxz

* = 8 + n * 116 where n = [0, 1, ..., numberOfEntries-1]

Recommended MIME type application/fxx.

Recommended file extension .fxx.

Status

Currently in beta. I want to review the synth and see if I can adjust the params to reduce the amount that create empty or "bad" sounds. Juice the most information out of those bits!

I also want to investigate using the full float32 range or expanding the recommended range and see what impact that will have, but I need to learn more about how the synth operates to be sure. This could also involve humanizing the units somewhat but it will require learning a lot more about the internals of the synthesis.

Glossary

• freq: frequency
• LPF: Low pass filter
• vol: Volume