How to stop running out of headroom in Smaart [GSwSST22]

by: Nathan Lively

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Transcript:

[0.789]
sound design so as I was doing those previous videos I kept getting kind of disappointed that I was running out of head room on my microphone preamp I kept wanting to turn it up more and more to make sure that I could get 20 DB of headroom between the noise floor and my measurement signal in the room across the frequency range but I kept running out of headroom in the very very low frequencies so I started wondering what would I need to do to make sure that I always had enough Headroom and I realized well I just need to make sure that whatever the loudest signal is gonna be that I start out 20 DB below that so here is an alternative method that I might start using in the field to make sure that I always have an F Headroom so I have my giant input meters open here to make this really easy and it's gonna take just a couple more steps of back-and-forth setting the level in the room to really make this work so first of all over here in my x32 I have the volume all the way down okay so no volumes going into the room but the tap is coming before this fader for the reference loop so when I turn on the signal gin here I'll should still be able to see it yep there we go so here's my reference I've got this is zero DB a pink noise right now what I want to make sure is that I can go 20 deep you know have 20 DB of headroom to basically do whatever I want and to make this even more clear I'm going to set this to a sine wave for now okay so this is zero DB and I've got this sine wave going here then as I look over here at my microphone preamp I can see that it's turned all the way down and if I start to turn it up then it's gonna go into clipping right okay so if I want to stay out of the red and stay in a safe zone even if I go all the way up to zero on my signal generator then I'll probably just leave this all the way down okay that seems safe you now I know that I can start at minus 20 DB and I'll have minus 28 DB here and over here I set this trim already so that it also wouldn't go into clipping and you can see here that they match which is nice so minus 20 DB on my input minus 20 DB on the signal generator and again I see that I can go all the way up I'm not clipping my input on my console I'm not clipping the input meters of my audio interface so I should be able to do whatever I want as long as I set the correct volume now in the room so let's go back down to 20 DB and what I want to do first is just take a measurement of the noise floor in the room and then turn the signal up so that I make sure I get at least above the noise floor at minus 20 DB so minus 20 DB will be my minimum level so that I'm above the noise floor throughout the frequency range and that I'm measuring and then all the way up to zero will be my 20 DB of headroom that I need to make sure that I get maximum coherence and my transfer function right I'll just turn up my microphone gain here to just kind of a random amount at this point so I can just take a measurement and I'll stop talking and we will get a measurement of the noise floor in the room right now now I'm going to start bringing up the signal in the room that's this fader over here and I don't one sign on one pink


[243.52]
down to 50 Hertz I am well above the noise floor okay so this will be my minimum measurement spot in here on my console that's -15 okay I'll just sort of note those and remember those and now now that I have the level set in the room now I can actually match my microphone preamp to my reference input so let's do that I would like to do that with a sign hopefully it doesn't kill me


[287.71]
okay so now I'm now I matched my reference to my measurement in the room that way when I go to my transfer function I've got a measurement that is around the zero DB line right and now I should be able to go from minus 20 DB up to zero and get maximum coherence if I need to so let's just take a look at that it's gonna be pretty loud here in the room we'll see if I can stand it


[324.849]
all right so it worked here's a noise floor I'm at my minimum measurement level here - 20 dB I am above the noise floor at all frequencies down to 50 Hertz now we know that for me to get maximum coherence I'm gonna need to be at least 20 DB above the noise floor so let's do an offset of our noise floor and then see what we have to turn our measurement up to throughout most of the frequency range I'm already above the noise floor I'm already 20 DB above the noise floor it's really in these low frequencies that now I'm covered up so let's take a look at that


[372.78]
so I guess my question is how high do I need to go and I know I can go up to zero and that may be what I need to do


[383.81]
it's getting pretty loud in the room so let's turn on our pseudo-random below 150 and just look at that


[396.68]
[Music]


[421.71]
[Music] okay so yes it does look like I would need to turn it all the way up to zero dB if I want to get above those cars driving by in the low frequencies here down to 44 and it looks like probably below 40 the speaker isn't doing much anyway all right so let's review this test if I want to make sure that I can get 20 DB above the noise floor then what I need to do is start at minus 20 on my signal generator in the room turn up my sound system and tell I'm above the noise floor throughout the frequency range and then I know that I'll have that Headroom okay and I just need to make sure that my reference in my measurement microphone inputs are matched on the preamps at that point so I know there was a lot of jumping around in this video what I'll try and do in the description below this video is I'll write all of these steps out step by step so that it's probably a little bit more obvious than this whole video anyway let me know you think about this process maybe you're doing something like this in the field already and maybe you have something maybe a little bit more simplified version of this but I hope this is helpful for you sound design



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___ I love to geek out about the physics of sound. This channel focuses on the growing opportunity for live sound engineers to improve their confidence and consistency through the understanding of the principles of sound system design and optimization. My goal is to make this channel upfront and honest about my success and failure, so you can learn from both. I am always open to suggestions and feedback so please comment on this video or contact me through my site.
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