compression question (hey that rhymes)

Discussion in 'Mixing & Song Critique' started by jalipaz, Nov 7, 2001.

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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 AtackDistinguished Member

Joined:
May 29, 2001
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

Joined:
Feb 10, 2001
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

Joined:
Feb 12, 2001
Location:
Bloomington, IL
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

Joined:
Sep 5, 2000
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 AtackDistinguished Member

Joined:
May 29, 2001
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

Joined:
Sep 5, 2000
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

Joined:
Feb 10, 2001
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?

Joined:
May 29, 2001
:w:

17. Jason PoffGuest

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

Jason