# compression question (hey that rhymes)

Discussion in 'Tracking / Mixing / Editing' started by jalipaz, Nov 7, 2001.

1. ### jalipazGuest

ok heres the example:
threshold: 15db
ratio: 5:1
so does that mean every 5db the signal goes over 15 it allows 1db? so it would be 16db. right?

heres another:
threshold: 10db
ratio: 3:1
so every 3db the signal goes over 10 it allows 1db. so it would be 11db. right?

ok one more:
threshold: 15db
ratio: 3:1
so every 3db the signal goes over 15 it allows 1db. so it would 16db again. right?
thanx for ur time,
jal

2. ### mapostelGuest

Hi Jal,
that's about right. It looks as follows:

Level In | Level out
example 1

13 | 13
14 | 14
15 | 15
20 | 16
25 | 17
30 | 18

example 2
8 | 8
9 | 9
10 | 10
13 | 11
16 | 12
19 | 13

example 3
13 | 13
14 | 14
15 | 15
18 | 16
21 | 17
24 | 18

PLEASE NOTE: Thresholds in reality are of course usually negative, i.e. the levels would rise like -14, -13, -12... etc.

Hope this clarifies,

Matthias

3. ### jalipazGuest

hey matthias,
it probably should clarify but it doesnt. im not sure which is ur threshold and what is ur ratio:
Level In Level out
example 1 13 13.... is it 1:13 ratio or what i dont get it.
14 14
15 15
20 16
25 17
30 18
can u explain like i did. im sorry if im a lil slow.
thanx,
jal

4. ### mapostelGuest

hey matthias,
it probably should clarify but it doesnt. im not sure which is ur threshold and what is ur ratio:
Level In Level out
example 1 13 13.... is it 1:13 ratio or what i dont get it.
Hi Jal,

Yeah, it's a bit difficult because it's hard to make a proper table with this interface.
OK, I was referring to your three examples, i.e. taking the threshold and ratio you were mentioning. And all I did was to draw up a table to show how the Out level relates to the increasing in level. you could draw a graph from it and would see how the compression curve flattens above the threshold.
But your thinking of the first post was right.

cheers

Matthias

BTW: I've edited my post - maybe it makes more sense now... ?

ok!! thanx!
jal

6. ### Jon AtackMember

Hi Jal,

You are correct. In practice, keep in mind that the attack and release settings will have a big, audible effect on the compression envelope. Use your ears. Happy compressing,

Jon

7. ### anonymousGuests

and one other factor skews the numbers a bit as well - hard knee or soft knee. Your hard knee will give you pretty much the math in the tables, but soft knee will throw a bit of a curve into the numbers that are closest to the actual threshold.

8. ### jalipazGuest

thanx little dog

9. ### drumsoundActive Member

Originally posted by jal:
ok heres the example:
threshold: 15db
ratio: 5:1
so does that mean every 5db the signal goes over 15 it allows 1db? so it would be 16db. right?

heres another:
threshold: 10db
ratio: 3:1
so every 3db the signal goes over 10 it allows 1db. so it would be 11db. right?

ok one more:
threshold: 15db
ratio: 3:1
so every 3db the signal goes over 15 it allows 1db. so it would 16db again. right?
thanx for ur time,
jal

Jal,
By your definitions in your post I don't think you quite understand the relationship of Threshold and Ratio. The way it works is: if the input signal goes over the threshold, its level is reduced (compressed) by the ratio. Audio under the threshold will not be effected. I'm math--phobic so I won't try to give actual numbers, Matthias has done that for you.

10. ### jalipazGuest

no i did understand that part i was just trying to understand exactly what the ratio does, cause ive heard and read a couple different things. i couldve read them wrong.
but i just wanted to make sure and now i know.
thanx guys,
jal
anyways isnt it he ear thats always right in this game thats why i love recording soooo much.

11. ### Ang1970Well-Known Member

Being negative, the dB number represents distance from the zero reference... in other words, when the signal is at -20, it is 20dB lower than 0dB. With that in mind, here is a new way of looking at the table.

Threshhold -15, Ratio 5:1
These settings mean that the compressor will pass 1dB for every 5dB above -15 that is fed into it.
INP=input level
OUT=output level
OVER=amount over threshhold
PASS=amount of signal passed over threshhold
REDUC=amount of reduction

• INP | OUT | OVER | PASS | REDUC
• -20 | -20.0 | 00.0 | 0.0 | -00.0
• -17 | -17.0 | 00.0 | 0.0 | -00.0
• -15 | -15.0 | 00.0 | 0.0 | -00.0
• -12 | -14.4 | 03.0 | 0.6 | -02.6
• -10 | -14.0 | 05.0 | 1.0 | -04.0
• -07 | -13.4 | 08.0 | 1.6 | -05.4
• -05 | -13.0 | 10.0 | 2.0 | -08.0
• -02 | -12.4 | 13.0 | 2.6 | -10.4
• -00 | -12.0 | 15.0 | 3.0 | -12.0
• +01 | -11.8 | 16.0 | 3.2 | -12.8
• +02 | -11.6 | 17.0 | 3.4 | -13.6
• +03 | -11.4 | 18.0 | 3.6 | -14.4
• +05 | -11.0 | 20.0 | 4.0 | -16.0
When the signal is at -10, it is 5dB above the threshhold of -15. The compressor reduces the gain by 4dB, allowing the output level to be -14, or 1dB above the threshhold of -15.

Hope that helps.

12. ### jalipazGuest

thanx that was great.
jal

13. ### Jon AtackMember

True. Though, it is indeed possible on many compressors for the threshold to be a positive dB number as well, like jal indicated in his table.

Jon

14. ### Ang1970Well-Known Member

Yes, I could have kept the table going into positive input values... I'll work on it in a bit...

Threshhold +5, Ratio 5:1
These settings mean that the compressor will pass 1dB for every 5dB above +5dB that is fed into it.
INP=input level
OUT=output level
OVER=amount over threshhold
PASS=amount of signal passed over threshhold
REDUC=amount of reduction

• INP | OUT | OVER | PASS | REDUC
• -20 | -20.0 | 00.0 | 0.0 | -00.0
• -15 | -15.0 | 00.0 | 0.0 | -00.0
• -10 | -10.0 | 00.0 | 0.0 | -00.0
• -05 | -05.0 | 00.0 | 0.0 | -00.0
• -00 | -00.0 | 00.0 | 0.0 | -00.0
• +05 | +05.0 | 00.0 | 0.0 | -00.0
• +06 | +05.2 | 01.0 | 0.2 | -00.8
• +08 | +05.6 | 03.0 | 0.6 | -02.4
• +10 | +06.0 | 05.0 | 1.0 | -04.0
• +12 | +06.4 | 07.0 | 1.4 | -05.6
• +15 | +07.0 | 10.0 | 2.0 | -08.0
• +18 | +07.6 | 13.0 | 2.6 | -10.4
• +22 | +08.4 | 17.0 | 3.4 | -13.6

15. ### anonymousGuests

All perfectly clear, unless you venture into the alternate universe of Joe Meek compressors - in which case none of this will have any meaning at all. Anyone offering a "Meek as a 2nd Language" course?

:w:

17. ### Jason PoffGuest

The threshold is a set value. To lower the threshold you raise the input.

Jason