Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Joseph D. Macry]

I installed a new sound system in an elementary school cafeteria. During commissioning, the design consultant set compressor/limiter in DSP at 100:1 ratio, +5dbu threshold. (The DSP is Biamp Nexia SP.) I thought the ratio was rather excessive, but hey he's the consultant.
Today, while investigating a report of distortion in the microphones, I found the comp/limiter hitting a few db of GR sounded rather ugly. (Had to get close and loud on the mic to hit the limiter.) So I eased back on the ratio to 20:1, which sounded much better. Still, I backed off the mic trims a tad.
The distortion was not reported by the users, but by the consultant. The school staff don't use the mic this loud.
Now the consultant wants me to put the ratio back to 100:1, but raise the threshold by "+10 or 15dB". I can do that, sure.

The question: What would you use for a limiter ratio, when the purpose is the protect the system from damage from transients?

[Ivan Beaver]

I installed a new sound system in an elementary school cafeteria. During commissioning, the design consultant set compressor/limiter in DSP at 100:1 ratio, +5dbu threshold. (The DSP is Biamp Nexia SP.) I thought the ratio was rather excessive, but hey he's the consultant.
Today, while investigating a report of distortion in the microphones, I found the comp/limiter hitting a few db of GR sounded rather ugly. (Had to get close and loud on the mic to hit the limiter.) So I eased back on the ratio to 20:1, which sounded much better. Still, I backed off the mic trims a tad.
The distortion was not reported by the users, but by the consultant. The school staff don't use the mic this loud.
Now the consultant wants me to put the ratio back to 100:1, but raise the threshold by "+10 or 15dB". I can do that, sure.

The question: What would you use for a limiter ratio, when the purpose is the protect the system from damage from transients?

The threshold could be anything-the individual numbers mean NOTHING-unless you know the rest of the system-like the rest of the gain in the system-the ratings of the loudspeakers and so forth.

I hope SOMEBODY realizes that by raising the output to +15 you are allowing TEN TIMES the power to go to the speaker system???

Is it rated for that-can the do it without clipping???/

There are bigger questions than the ratio.  I think something else is going on.

[Jason Lavoie]

I installed a new sound system in an elementary school cafeteria. During commissioning, the design consultant set compressor/limiter in DSP at 100:1 ratio, +5dbu threshold. (The DSP is Biamp Nexia SP.) I thought the ratio was rather excessive, but hey he's the consultant.
Today, while investigating a report of distortion in the microphones, I found the comp/limiter hitting a few db of GR sounded rather ugly. (Had to get close and loud on the mic to hit the limiter.) So I eased back on the ratio to 20:1, which sounded much better. Still, I backed off the mic trims a tad.
The distortion was not reported by the users, but by the consultant. The school staff don't use the mic this loud.
Now the consultant wants me to put the ratio back to 100:1, but raise the threshold by "+10 or 15dB". I can do that, sure.

The question: What would you use for a limiter ratio, when the purpose is the protect the system from damage from transients?

In the strictest terms, for a "limiter" you want the ratio as high as possible, otherwise it's just a compressor.

Jason

[Steve M Smith]

In the strictest terms, for a "limiter" you want the ratio as high as possible, otherwise it's just a compressor.

Surely, it's equally a function of the threshold.

If you have a signal averaging 0dB going in and the threshold is at +3dB, it's going to limit.  If the threshold is down to -20dB with the same signal, it's going to compress.


Steve.

[John Roberts {JR}]

Surely, it's equally a function of the threshold.

If you have a signal averaging 0dB going in and the threshold is at +3dB, it's going to limit.  If the threshold is down to -20dB with the same signal, it's going to compress.


Steve.

Sorry to disagree but no... a limiter with the threshold set for -20dB will limit at -20dB.

Compression describes reducing signal level changes proportionately reducing the gain X dB for every Y dB signal change above a given threshold so the sound is similar to before just less dynamic. Limiting describes reducing the gain whatever it takes to prevent the signal exceeding the limit threshold.

Compression is used as an effect to improve the sound quality. Limiting is generally used to protect gear from overpowering.

Of course this is the short description but close enough.

JR

[Steve M Smith]

Sorry to disagree but no... a limiter with the threshold set for -20dB will limit at -20dB.

Yes.  You're absolutely right.

I generally think of compression as something which is active all the time and limiting as something to catch the peaks.

I could be wrong though as I have been wrong in the past.  I think it was once in 1984 and again in 1997!


Steve.

[John Roberts {JR}]

Yes.  You're absolutely right.

I generally think of compression as something which is active all the time and limiting as something to catch the peaks.

There are different flavors of compression involving variation in behavior around the threshold (like soft-knee). There are also full range compressors that do not have a threshold (like 2:1 compression used in old DBX tape noise reduction encoder.)

I could be wrong though as I have been wrong in the past.  I think it was once in 1984 and again in 1997!


Steve.

I thought I was wrong once, but I was mistaken.... 

JR

[Joseph D. Macry]

To clarify:

The signal level in DSP peaks between +5 and +8 dBu, producing a pretty loud program in the school Cafetorium. The limiter was set at +5, so a loud voice was causing the limiter to kick in, and it sounded lousy. I found it to sound better with the milder 20:1 ratio, but the consultant wants to keep the stiff 100:1 ratio while raising the threshold up to where something unusual (say, a dropped mic) would be required to hit the gain reduction.

The block in DSP is called "Compressor/Limiter". A limiter is simply a compressor with a rather high ratio and a threshold set above normal operating range.

[John Roberts {JR}]

To clarify:

The signal level in DSP peaks between +5 and +8 dBu, producing a pretty loud program in the school Cafetorium. The limiter was set at +5, so a loud voice was causing the limiter to kick in, and it sounded lousy. I found it to sound better with the milder 20:1 ratio, but the consultant wants to keep the stiff 100:1 ratio while raising the threshold up to where something unusual (say, a dropped mic) would be required to hit the gain reduction.

Either the system needs to be limited at +5 or it doesn't. Turning down the ratio, or raising the threshold reduces the amount of system protection.

If it sounds bad from 3dB of limiting  (+8 dB - +5 dB) there may be something else wrong. In fact limiters do not have to sound bad, even when they are seriously limiting. 

The block in DSP is called "Compressor/Limiter". A limiter is simply a compressor with a rather high ratio and a threshold set above normal operating range.

Perhaps in their mind. While they both are similar in that they reduce gain above a threshold, limiters (for protection) generally use faster attack and faster release times than compressors which serve a somewhat different purpose (gentle sound shaping). 

If vocals are hitting the system limiter hard enough to sound bad, maybe turn down the vocal, or buy a bigger system that plays louder?

JR

[Mac Kerr]

If vocals are hitting the system limiter hard enough to sound bad, maybe turn down the vocal, or buy a bigger system that plays louder?

Yes, this.

[ProSoundWeb Community]