Audacity Compressor - ideas for improved parameter entries


1	Concepts:
2	1.	GUI "Slider" parameters should be evenly distributed according to pyscho-acoustics. In many cases, this entails logarithmic scaling (e.g. powers of 2).
3	2.	I think the GUI Slider for Threshold in v2.1.1 is good as-is. The thing about Threshold is that it could be anywhere, and a person stills needs precision of 1 dB or less. It is not practical to do some sort of logarithmic scaling here (beyond the already logarithmic dB scale).
4	3.	GUI should be wide enough to allow easy fine adjustment of the stepped list of GUI Slider parameters. In v2.1.1, I think the GUI seems too narrow to allow this.
5	4.	There should be support for Non-GUI parameters, providing more advanced functionality via manual editing of App Data chain script files.
6	5.	All parameters should: 1) Have "extended range" beyond what is offered by the GUI Sliders. 2) Allow continuously variable parameter values, precise to at least 3 significant digits throughout the entire valid range. However, GUI Slider parameters are probably ok to limit to 2 significant digits.
7	About Me:
8	My name is Jimmy and my handle on the Audacity forum is "jimmyhosen". My background is mainly live sound reinforcement, which means I might be unaware of some of the needs faced in the studio. I have updated this spreadsheet a few times, based upon further thought and based upon insight from some of the great guys on the Audacity Forum (Steve, Gale, etc.). However, overall, this spreadsheet does contain my current personal opinions. You can view my feature request here:
9		http://forum.audacityteam.org/viewtopic.php?f=20&t=87604
10	Last update to this spreadsheet:	2015-09-17 at 12:45 MST (Arizona, USA)


1	Ideas for Compressor's GUI Slider values for: NOISE FLOOR
2	3 dB per Step
3	Step Count	NF Threshold

4	1	-18
5	2	-21
6	3	-24
7	4	-27
8	5	-30
9	6	-33
10	7	-36
11	8	-39
12	9	-42
13	10	-45
14	11	-48
15	12	-51
16	13	-54
17	14	-57
18	15	-60
19	16	-63
20	17	-66
21	18	-69
22	19	-72
23	20	-75
24	21	-78
25	22	-81
26	23	-84


1	Ideas for Compressor's GUI Slider values for: RATIO
2	Ratio = a^(b/c)
3	a	b	c	Ratio (x:1)

4	2	1	4	1.19
5	2	2	4	1.41
6	2	3	4	1.68
7	2	4	4	2
8	2	5	4	2.4
9	2	6	4	2.8
10	2	7	4	3.4
11	2	8	4	4
12	2	9	4	4.8
13	2	10	4	5.7
14	2	11	4	6.7
15	2	12	4	8
16	2	13	4	9.5
17	2	14	4	11.3
18	2	15	4	13.5
19	2	16	4	16


1	Ideas for Compressor's GUI Slider values for: ATTACK TIME
2	Attack Time measurements are in milliseconds, not seconds, because most of the range is less than 1 second. Note that half of the Attack Time values in this table are below the current range lower limit of 100 ms.
3	Attack Time = a^(b/c)
4	a	b	c	Attack Time (ms)	Lowest Recommended Freq. in Passband (Hz)

5	2	4	2	4	125
6	2	5	2	6	88
7	2	6	2	8	63
8	2	7	2	11	44
9	2	8	2	16	31
10	2	9	2	23	22
11	2	10	2	32	16
12	2	11	2	45	11
13	2	12	2	64	8
14	2	13	2	91	6
15	2	14	2	128	4
16	2	15	2	181	3
17	2	16	2	256	2
18	2	17	2	362	1
19	2	18	2	512	1
20	2	19	2	724	1
21	2	20	2	1,024	0
22	2	21	2	1,448	0
23	2	22	2	2,048	0
24	2	23	2	2,896	0
25	2	24	2	4,096	0
26	2	25	2	5,793	0


1	Ideas for Compressor's GUI Slider values for: RELEASE TIME
2	Release Time = a^(b/c)*d 2^(3/2) = 2.83 (approx.)
3	a	b	c	d	Release Time (seconds)

4	2	0	2.83	0.5	0.50
5	2	1	2.83	0.5	0.64
6	2	2	2.83	0.5	0.82
7	2	3	2.83	0.5	1.0
8	2	4	2.83	0.5	1.3
9	2	5	2.83	0.5	1.7
10	2	6	2.83	0.5	2.2
11	2	7	2.83	0.5	2.8
12	2	8	2.83	0.5	3.6
13	2	9	2.83	0.5	4.5
14	2	10	2.83	0.5	5.8
15	2	11	2.83	0.5	7.4
16	2	12	2.83	0.5	9.5
17	2	13	2.83	0.5	12
18	2	14	2.83	0.5	15
19	2	15	2.83	0.5	20
20	2	16	2.83	0.5	25
21	2	17	2.83	0.5	32


1	These ranges would extend beyond what is available via the GUI Sliders, and would only be accessible via: 1) text fields in the GUI. 2) manual editing of Chain files in a text editor or source code editor like Notepad++.
2	Parameter Type	Range		Unit of Measure	Notes
3	Parameter Type	Lower Limit	Upper Limit	Unit of Measure	Notes

4	Threshold	-60	-1	dB	I am not sure whether anything below -60 dB is practical. Program material that has a crest factor larger than 78 dB is probably extremely rare. In that case, I would probably employ a multi-stage compressor via chain script.
5	Noise Floor	-84	-18	dB	Each limit resides on a multiple of 6 dB. I assume that people working in 24-bit audio might want something down to -84 dB.
6	Ratio	1:1	32:1	dB	It is important to have good functionality below 2:1. This is not only useful for Spoken Word, but also for Mastering.
7	Attack Time	2	10000	milliseconds	On a logarithmic scale (powers of 2), most of the range suggested here is less than 1 second. Thus, in the GUI, I think things should be listed in milliseconds, not seconds. For programming purposes, I could see how Seconds might be better in the source code, also including Chain script files. I have never [yet] needed anything longer than 25 ms. Steve (in Audacity Forum) informed me of a couple situations that might require long Attack Times, up to at least 5 seconds. (Steve, thank you for the insight!) Considering that the period of 20 Hz is 50 ms, I do not understand why the Compressor in v2.1.1 does not support any Attack Times below 100 ms. I believe that times down to 4 ms should be on the GUI Slider. Even though this is a "lookahead" compressor, for Spoken Word, I find the downward pumping at 100 ms (and longer) to be audible and annoying. I am surpised at the 100 ms limitation because so many people use Audacity for podcasts of Spoken Word.
8	Release Time	0.050 (i.e. 50 ms)	60	seconds	I think it is important to offer Release Times below 1 second. In acoustically dead environments, I often use less than 1 second for Spoken Word, down near 0.5 seconds (500 ms).