Ive been designing a compressor pedal and run into a problem on the atck/dcay times. Trying to match the ssl bus compressor that has attack times of .1 1 30 ms and decay times of .1 .3 1s decay times. These times are only half the info. How many dbs does it compress in that time? The full 60db or a more practical number like 10 or 20db? The pedal design in LTspice shows db/ms. How do I relate these two?
Last edited:
Hi, threshold adjust pot is often used in compressors. Compression occurs when the signal level goes above the threshold. You could set some predefined well chosen threshold and let user adjust input and output volume instead. This is more intuitive than threshold knob me thinks, in an effects box.
How much compression depends on compression ratio, which is often adjustable in compressors as well. I think the most usefull ratios are 2:1 - 4:1. After ratio maybe around 10:1 you would go into limiting territory, which could be fun with an effects box.
If ratio is 2:1 and input tries to rise 6db above the threshold, your compressor kicks in after attack time and compresses the signal and lets it rise only 3db (2:1 ratio) above the threshold. This compression is then released in release time (your decay) after the signal has dropped below the threshold.
You could find this and more by searching the web, for example Keeley compressor was popular diy compression pedal project 15 years back. Check out GroupDIY - Index and you'll find multiple versions of SSL bus compressor discussed with thousands of forum posts. Have fun!🙂
How much compression depends on compression ratio, which is often adjustable in compressors as well. I think the most usefull ratios are 2:1 - 4:1. After ratio maybe around 10:1 you would go into limiting territory, which could be fun with an effects box.
If ratio is 2:1 and input tries to rise 6db above the threshold, your compressor kicks in after attack time and compresses the signal and lets it rise only 3db (2:1 ratio) above the threshold. This compression is then released in release time (your decay) after the signal has dropped below the threshold.
You could find this and more by searching the web, for example Keeley compressor was popular diy compression pedal project 15 years back. Check out GroupDIY - Index and you'll find multiple versions of SSL bus compressor discussed with thousands of forum posts. Have fun!🙂
Last edited:
Thank you. Hopefully that wasn't a waste of your time and someone can use that info. I asked a very specific question to try and get a very specific answer. Ive searched the web and I havent found it. Some compressors express attac/decay times in db/ms while most are just in ms. How do they relate?
Wowza, yeah sorry, it's late here 😀 Gearslutz have it discussed of course, for example here Symetrix 501 and DBX 160SL seem to be compressors with such dials, so maybe manuals reveal more? Symetrix 501 Attack and Release Time Question - Gearslutz
Thanks again. Just saw that, but again no specifics, but theres clues there.Then this from wikipedia: For more intuitive operation, a compressor's attack and release controls are labeled as a unit of time (often milliseconds). This is the amount of time it takes for the gain to change a set amount of dB or a set percentage towards the target gain. There is no industry standard for the exact meaning of these time parameters.
Ill keep searching maybe find something more specific.
Ill keep searching maybe find something more specific.
Short answer, you are asking too much 😛
Too sleepy now for a better answer (it´s 5 AM here) , will try to improve it but the core is what I wrote above.
I know there must be some way to at least relate both .
Too sleepy now for a better answer (it´s 5 AM here) , will try to improve it but the core is what I wrote above.
I know there must be some way to at least relate both .
This is in answer to your original question. Take for example an optical compressor. The LDR has a response time which can be tailored with additional filters to slow down the current rise/drop of the LED current. The LED current translates to a resistance value of the LDR. Once you have determined the rise/fall time, they stay constant.
The resistance of the LDR is in parallel with another resistor that limits the range of compression. Having built such a compressor for guitar, I think 20dB compression range is sufficient. Higher compression ratios can exacerbate noise pumping and rob the sound of dynamics. In the end you decide the parameters on audition.
The resistance of the LDR is in parallel with another resistor that limits the range of compression. Having built such a compressor for guitar, I think 20dB compression range is sufficient. Higher compression ratios can exacerbate noise pumping and rob the sound of dynamics. In the end you decide the parameters on audition.