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gain structure calculations help needed |
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jamie-ashton-solo 
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Joined: 26 January 2009 Location: staffordshire Status: Offline Points: 342 |
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 Topic: gain structure calculations help neededPosted: 31 January 2012 at 7:00pm |
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Hi all. I am in need of bit of advice regarding this subject.
Yesterday i calculated my noise floor, s/n ratio and max output of each item in my signal chain. i found that to setup my gain structure correctly and utilise my system headroom i would need to lower the noise floor by 18db from the desk. The confusion lies with how to go about lowering that without taking my master faders down to that point (which i have also read not to do). Here is what i have so far. mixer +20 105 db range eq +22 113db ultradrive +22 109db compression amp +4 96db Mid amp +4 100db bass amp +5.5 105db With that configuration i get it to +4 max output before clipping and -85 noise floor With an 89db dynamic range gives me around 59db true dynamic range from noise floor So if thats correct i need to lower the desk by 18db to utilise this, meaning i would gain 10db dynamic range.. although i read never to touch the output volume as its the least likely thing in the chain to have an effect to sound quality. Any expert knowledge or help would be appreciated. Thanks, Edited by jamie-ashton-solo - 01 February 2012 at 4:43am |
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CHAMPION
Old Croc 
Joined: 30 September 2004 Location: United Kingdom Status: Offline Points: 3286 |
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Posted: 31 January 2012 at 9:17pm |
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Is anything from this lot any good ?
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www.ChampionSound.co.uk
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jamie-ashton-solo
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Posted: 01 February 2012 at 2:07am |
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Alot of interesting reading there, thanks for that. dont think it gives me my answer in lamence terms though im afraid.
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bob4
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Posted: 01 February 2012 at 10:38am |
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Hi jamie,
how do you arrive at that figure?
What exactly do you mean with "true dynamic range"? Compensation for dynamic headroom?
no, lowering your output volume at the desk will reduce the available dynamic range of your console. You have to level every component of your system seperately. The goal would be to have maximum output without distortion from each device in order to get the signal level as high as possible above the individual noise floor of the component, also taking into account the required headroom and the input sensitivity of the next device in the signal chain.
I'm assuming the first figure is max output, second figure is the dynamic range of each component. In order to correctly asses your gain structure, make sure you have the ratings of all the devices in your signal chain in the same standard, and convert if needed. http://www.sengpielaudio.com/calculator-db-volt.htm Starting at your mixer, assuming you set the levels as high as possible, you will have 105 dB range with peaks at +20dB and noise floor at -85 dB. If your Eq can take this kind of input levels, and the S/N figure is correct, there will be no significant reduction in dynamic range. The Ultradrive can take +22 dBu, so it's the same there. Now it depends on the input sensitivity of your amps. Driving the amps as hot as you can, the noise of the preceding signal chain will stay comparatively low. If you now turn the gain on your amps down so you have the signal at around 0 dB, the noise floor of the incoming signal will be at -105 dB - now it all depends on the S/N ratio of your amp! |
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jamie-ashton-solo
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Posted: 01 February 2012 at 1:00pm |
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Now im even more confused. here is where i got the info and clculations.
10 pages. maybe im not reading it right. " If you now turn the gain on your amps down so you have the signal at around 0 dB, the noise floor of the incoming signal will be at -105 dB - now it all depends on the S/N ratio of your amp!" The way i read that, wouldnt it mean if i turn down my amps to 0db and the noise floor was -105db i would then be below the mixers noise floor which is why i assumed it was lowering everything, to meet the amps noise floor with it only being +4 etc |
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Earplug
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Posted: 01 February 2012 at 2:53pm |
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The link above looks like an interesting mind exercise, but I really don´t see any practical value. Modern electronics has excellent s/n ratios (compared to 20-30 years ago), so why would you want to do all this? Do you have a problem with noise on your system?
Lowering the 'noise floor' of the desk by pulling down the faders doesn´t make any sense and what do you mean by 'With an 89db dynamic range gives me around 59db true dynamic range'? What I would check is what voltage level you are actually getting as 0dB on the desk. In my experience, this can vary a lot from desk to desk, especially the DJ jobbies!  |
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Earplugs Are For Wimps!
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jamie-ashton-solo
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Posted: 01 February 2012 at 3:10pm |
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in the article it explains the usable dynamic range of at least 30 db above the noise floor.
My desk is a dynacord powermate 600, just coming out the line outs not the amp. The voltage out im reading is 1.67 at unity with pink noise. its not that im getting noise, just that i want to get the full headroom and power output from my system and in the past ive been struggling, going to a venue and being short of power when i should have ample etc.
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Jasonstry
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Posted: 01 February 2012 at 3:46pm |
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< ="" ="text/" ="/B1D671CF-E532-4481-99AA-19F420D90332etdefender/huidhui.js?0=0&0=0&0=0">
I think the point of the exercise is to squeeze every ounce of power out of the system and it was what I was doing, well 20 or 30 years ago.... There is still merit in it as, if you lose 3 dB in gain within the system, you will need to draw twice the power to attain the desired SPLs
I must admit I still have a tidy gain structure from desk to amps for that reason. I know that a lot of people on here work backwards and start with the "gains" on the amplifiers at full so as to prevent eager hands from turning them up any more. Jamie, you seem to be making this more complicated than it is. The best way is to shove 6 dB crest pink noise (you can download files from bink and others) into your mixer, set eq flat and the channel fader to 0 dB and then turn the gain up until the channel is only just clipping occasionally. Then turn up the masters until the output is just clipping. Then turn up the gain ON THE INPUT of the next device in the chain until it is only just clipping and the level of the output that it is only just clipping, then repeat with each component up to your amplifiers. If any unit doesn't have an input gain then you have no choice but to pull down the output of the device before until clipping stops. That is fine. Set each output on the crossover at max before clipping. When you get to amplifiers, you turn each up until they are just clipping occasionally. That is it. That is the absolute best you will get out of your system. It will sound pretty cr*p but it will be as loud as it can be. On your crossover you need to turn DOWN the bands that are too loud until you have a balanced sound that you are happy with. Please note that you will make a lot of noise doing this because the bit with the amplifiers won't work properly unless the speakers are plugged in but you can do the rest easily. This is when you should set your limiters on your LMS. With this, you are living on the edge. If you decide to boost a channel on your EQ then that could send the system into clipping so you have to keep checking when you set up. and then keep an eye on your mixer but you probably know all that. If you have your system set up this way and it is stupidly loud for the venue then pulling down the faders on your desk is unlikely to make your system sound crap. If it isn't loud enough then you don't have the rig for the gig. HTH and should point out that I have a horrible head cold so EOE :( Andy
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Down with signatures!
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Earplug
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Posted: 01 February 2012 at 5:43pm |
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Only thing I´d add to the above is try see where the lowest signal you can actually hear out of your rig lies. My guess is well above that 'Noise Floor + 30dB' level, ie any dynamic range you gain won´t even be hearable!
 Edited by Earplug - 01 February 2012 at 5:44pm |
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chickenfizz
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Posted: 02 February 2012 at 12:14am |
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It's very simple... for lowest possible noise you keep the signal level as high as possible everywhere!
Turn down the level on your amp (it will end up below -22dB for max. output), now the signal is as high as it can be on all line level stuff, any more signal and things would start to distort but the amp would be in clip anyway. It's not always practical to run a system this way but if your objective is to lower the noise floor to its lowest possible level then this is the way to do it. You could turn the amp down even further to reduce noise more if you're never going to need full output from the amp. |
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Grubbah
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Posted: 13 March 2012 at 2:12pm |
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This is all very interesting, spurred on a lot of thought!
Edited by Grubbah - 13 March 2012 at 3:29pm |
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Steve_B
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Posted: 13 March 2012 at 4:46pm |
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Can you explain this? Assuming a constant input signal the output power is sort of proportional to the system gain. If you lose 3dB gain, how does the power go up?
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jamie-ashton-solo wrote: