Gain Staging - Episode 3

Hi, I'm David Mellor, Course Director of Audio Masterclass and in this Sound On Sound podcast series I'm talking about gain staging. I'm going to cover two topics today, more about preamps and gain staging in preparation for your mix. Hopefully you've already listened to my two previous episodes in this podcast series otherwise this, episode three, won't make as much sense as it should. You have listened to episodes one and two? Great. But, I'll still give you a couple of reminders. Firstly, in your digital audio workstation software, 0 VU is equivalent to -18 dBFS. Secondly, I'm talking about regular 16 bit or 24 bit WAV files. I will mention the 32 bit float format later on in this series, but for now we'll assume 16 bit or 24 bit. OK? Let's press on. More About Preamps More about preamps and gain staging in preparation for your mix. Just to recap on preamps, what I said in a nutshell is that in your sound check, you should watch the meter in your DAW and raise your preamp's gain until you get a good, strong reading. If you aim for a reading bouncing around -18 dBFS and peaking up to -12 or -10 or so, then you will be way above any noise in your 24 bit recording and you'll still have plenty of headroom to cope with unexpected peaks. This assumes that you're using the mic preamp that's built into your audio interface. I just have to check that because I've heard so often, I don't have a preamp. Yes, you do. It's built into your audio interface. But one complication is that you may have an additional separate preamp that connects to your audio interface. If you do, then you have another stage of gain staging to think about. But this is simple and it's only complicated by different equipment being different. The purpose of your preamp is, of course, to sound good. Otherwise, why did you buy it? But its other purpose, its inherent purpose, is to raise the rather weak signal from the microphone from mic level to line level. So what are mic level and line level? In home studio recording into your Digital Audio Workstation software, there isn't a lot to worry about here. Plug your microphone into a mic input. Anything that runs from mains power, connect to a line input. An instrument like an electric guitar or Rhodes piano, connect to an instrument input. There's quite a lot of explanation behind this, but I'll try to stick to things that will directly affect your gain staging. Microphone level, or mic level, doesn't seem to have an official exact figure, but I'll go along with what Shure says. When Shure says anything about microphones, you have to respect it. Shure describes mic level as “typically just a few thousandths of a volt”. That's a few millivolts, in other words. Line level, however, does have a definition, uh, definitions. For professional equipment, standard line level is +4 dBu, which will drive a standard physical VU meter up to zero. For domestic equipment, line level is -10 dBV, which is 10 decibels lower than 1 volt. Yes, it's easy to confuse dBU and dBV. Zero dBU is 0.775 volts. Zero dBV is 1 volt. I didn't invent this. What we can see, therefore, is that if a piece of audio equipment is made to the professional standard, then it expects line level to be +4 dBu, or 1.228 volts. If it's made to the domestic standard, then it expects line level to be -10 dBV, or 0.316 volts. Oh yes and there are such things as meters that look for all the world like standard VU meters but read 0 VU for an input of -10 dBV. This is the point where I have to say it's complicated. Now, let me sweep all of that irritating complication aside. The line input of your audio interface doesn't have a gain control. So all you have to do is connect the output of your preamp to the line input of your interface and proceed as before. Raise the gain on the preamp, so you see -18 dBFS peaking at -12, -10 or so. You see, gain staging isn't difficult but oh dear, here's a but - your audio interface may have a gain control on the line input. If it has, you're going to have to decide where to set it. It may be the case that the line input gain control is calibrated. If so then zero is the place to be. Zero decibels of gain, nothing higher, nothing lower, so no change to the signal. On the other hand it might be completely devoid of calibration. You know, I so much don't like this, but you may be able to stick your head into the manual and find out what position of the knob is zero. Or you may have a line input with a gain control on the front and line inputs with fixed gain on the back. You can find out by experiment and comparison where the zero position is on the front panel gain control, then mark it with a sharpie. You'll be relieved to know that I'm going to move on from this, but I'll add one more thing. If a gain control on any equipment is calibrated 0 to 10, then 0 probably isn't 0 decibels, meaning no change in level. It's either the lowest available setting, whatever that might be, or completely off. Preamps With Valves I will now move on to preamps that have a separate gain control and output level control. This is much simpler to explain. Typically this would be where you have a preamp that has a valve inside, or a tube if you prefer, or a vacuum tube if you prefer, or a thermionic tube if you prefer. I aim to please. I'll call it a valve. The point of using this old technology is that valves lend themselves to the creation of mild distortion, which we call warmth. Transistors lend themselves either to accuracy or to extreme distortion. So old though valve technology may be, it most definitely still has its place in audio. What would be nice, therefore, would be to be able to control the amount of warmth and with a valve preamp, or a preamp that has a valve, not quite the same thing but close enough for my purpose, you can have exactly that. At a low gain setting, a valve preamp can have low distortion, clean enough that you can have almost clinical accuracy if you want. But of course you want to get a good, strong reading on the meter in your DAW. A low gain setting isn't going to give you that and so there is an output level control. The level of the signal after the valve stage is boosted up, probably by transistors, to get the level you want. So, if you have a preamp like this and you want a clean, accurate recording, then set the gain low and the output high. If you want more warmth, set the gain high and compensate for that with the output level low. Let's have an example. Here's a vocal that I recorded in Abbey Road Studio 2. The singer is Nicola Dynes, the microphone an AEA A440 active ribbon, the preamplifier a Universal Audio Solo 610 and the song, well, it's just one of my doodles. I'll play one after the other, firstly low gain high output, then high gain low output. Listen for the thickening of the sound in the high gain example. “If I only had one day, I'd be pretty just for you. If I only had one day, I would dance only with you. All morning, afternoon and evening and the night time too. If I only had one day I'd share it with you”. “If I only had one day, I'd be pretty just for you. If I only had one day, I would dance only with you. All morning, afternoon and evening and the night time too. If I only had one day, I'd share it with you”. I've had plenty of opportunity to experiment with this technique in preamps from fairly cheap and cheerful to eye-wateringly expensive and I can tell you, it works. There seems to be something about embedding warmth right from the start, right there in the preamp, that isn't possible to match with processing later on, even genuine valve processing. There's also a certain degree of merit in deciding how you want your recording to sound and printing that to disc, rather than the endless tweaking that can happen when you leave your decisions to later, that mythical later that sometimes never comes and often never ends. The Mixing Process I've covered so far the signal path from original sound source, to microphone, to preamp, to audio interface, all the way into the digital audio workstation. At this point, you should have a perfectly gain staged recording which you can build up into a full production, ready to mix. OK, so let's mix it without plug-ins. That's daring, but you'd be surprised at what you can achieve with a bit of hard work. I'll need to come back to plug-ins and how they relate to gain staging later, because it's a whole different issue. There are a few fundamentals I need to address now and considering a full mix without plug-ins is, I think, the way to do it. But let's not be too ambitious, let's consider just a single track that you've just recorded. Your single track contains of course, a perfectly gain staged recording. It bounces around -18 dBFS, peaking up to -12, or -10 or so. Ha! Pull the other one. This is what happens in a perfect world. If you made the original recordings yourself and you were careful about gain staging, then this is exactly what you'll see. But in the white hot panic of recording, battling with musicians, mistakes, lightning in a bottle flashes of inspiration, your levels are probably all over the place and then you might be mixing someone else's recording, someone who hasn't listened to this podcast. So in the real world, your DAW session will have high levels, low levels, some tracks may even have nicely gain staged levels. So what do you do? Nothing. Just mix. I said this in an earlier episode. There's so little to go wrong and the DAW is so forgiving that you can get a perfectly professional and marketable mix without thinking at all about gain staging, as long as you don't clip anything. But I also said that it's useful to work to a method, so everything is always just as you expect it to be. Consistency may be the last refuge of the unimaginative, as Oscar Wilde said, but when you have a process that over time can become automatic, you can apply yourself to your music and creativity so much more efficiently. This one perfectly gain staged track, no let's not do that, let's think of a track that's very high in level, not clipped, but otherwise high. What's going to go wrong? Well, one track that's high in level isn't a problem, but two tracks that are high in level, three, many, this will push up the levels in your master track or channel, as I often prefer to call it because it isn't recorded onto a track. You'll see red lights at the top of the meter column. If you bounce this to a wave file, either 16 or 24 bits, it will clip because a regular wave file. can't go above 0 dBFS. The solution is to pull down the master fader and you can do this. Your DAW has massive internal headroom, absolutely massive. At this point, I think I better prove this with a demonstration. I'm going to play you some sine wave tones at my favourite frequency of 220Hz. Because of the requirements of podcasting, the levels you hear will be lower than I say, but the levels I'm using in my DAW will be exact and everything you hear will be in proportion. I'll start with 220Hz at -0.1 dBFS very close to the top, but not clipped. I'll bounce it to a wav file and let you hear the result. The Channel Fader and Master Fader will both be at zero. It sounds clean, as you would expect. Now, I'm going to duplicate the track and mix them together, leaving the faders at zero. I'll bounce this to a wave file, which sounds like... It's clipped. Of course, this is what we expect. If we mix two identical signals together, the level will rise by 6dB. This is 6dB into clipping. But what if I lower the master fader by 6dB? What will happen? Here's the result. It's clean! Although inside the DAW, I've pushed the level up to +6 dBFS. I have enough headroom internally to bring it down again and keep it clean. I can duplicate the track some more. What will happen is that for every doubling in the number of tracks, the level will increase by 6dB. I'm going to go crazy now, I’ll make 32 identical copies of my original track. I've doubled the track 5 times - each doubling raises the level 6dB. So the level internally is now +30 dBFS, actually a little lower because the original track is minus 0.1 dBFS. But it's close enough. What does this much clipping sound like? Very nasty, indeed. But I can lower the master fader by 30 dB, and... It's clean. This shows that my DAW has massive, massive internal headroom, and yours does too. And I could have doubled again and doubled again. So there's nothing wrong with pulling down the master fader and no reason you shouldn't do it. Except that it is a perfect demonstration of messy work. It's like a rust bubble in a second hand car you're considering buying. Every fault you can see conceals ten faults that you can't. So, if you're pulling down your master fader on a regular basis, that's easy to see. But all the other mess you've made isn't and it is affecting the sound of your mix. Of course, I don't mean you personally. I should have been using the royal one is making a mess. My advice is that one shouldn't. I need just to add here that there's no problem in shifting the master fader a couple, or even a few decibels up or down. But I'm thinking 3, 4, 5, certainly not 10 or 20. Let me go back to that one track you have. It could be a kick drum track. or bass drum if you prefer, and it's very high in level. What will happen, and it absolutely will happen, is that as you add in more instruments and vocals, you'll balance them against the kick and you'll end up pulling down the master fader. In fact, you'll tweak it down with every couple of new tracks you add to the mix. So what's the answer? Simple. Lower the kick right from the start. It depends on how many tracks you're using and also the genre of music even, how many decibels you should start off with. But after a few mixes, then if you keep this in mind, you'll know where you should start. Using VU Meters Did I say that gain staging doesn't have to be complicated? It isn’t, what I described is all you have to do. It's all you have to do. But there's one more thing you might want to do. This is where the VU meter comes back. You're listening to this podcast because you want to hear my view on gain staging. But my view and other people's views might be different. I don't mind that, differences are good as long as they're not wrong and don't lead you down a rabbit hole of any kind. So you're listening to this podcast and you've also watched YouTube videos on the topic of gain staging. Or you will watch YouTube videos on the topic of gain staging so that you'll get an all round view. I'd start with the one where an incredibly well respected mix engineer says that he doesn't gain stage. That will be a good grounding. But when you explore further, you'll find that a number of presenters use VU meters for gain staging. Plug-ins of course, not actual electromechanical ones. You might be advised to use a VU meter in every track. That seems like a lot, but if you look at photos of old style monster mixing consoles and multitrack tape recorders, you'll see all those VU meters. Electromechanical, too. Let's go through the process and see what we can achieve. Firstly, though, we need to know how to control level in the DAW. Level? That's simple, isn't it? Just move the faders. Well, it isn't quite so simple. Normally in the DAW, the faders come after the inserts. Except in the master channel, but I'll deal with that in a future episode. The fader also normally comes after the meter in the track. DAWs differ in how you can set your preferences, but these are good norms to work with. So you're looking at the meter in the track and it doesn't change when you move the fader. This isn't going to help you gain stage. So what you need therefore is a method of changing the level that comes before the fader and in general there are two ways to do it. It's a complication that DAWs differ, but what you can expect in most DAWs, perhaps all of them, but there are too many for me to test them all, is that you can adjust track gain, or clip gain, right there in the track. This is before the meter and before the fader. Another way is to insert a trim plug-in into the track, as the first insert. Again, you can adjust the level of the track before the meter and before the fader and your second insert, a VU meter, of course. In my thought example, the level on this one track is high, but you can now adjust it with Track Gain, Clip Gain, or your Trim plug-in and you can judge the level on your VU meter. What level should you set? Say it out loud. I almost heard that. Bouncing around -18 dBFS, peaking around -12 or -10, or translated into volume unit language, bouncing around 0 VU. This is gain staging. It's purely technical and it gets your signal to a good level to be ready to mix. You'll mix with your faders. Purely for the artistic result and not be bothered with technical issues, because you've dealt with them already. You can do this for every track. I'm going to bring my own opinion back in again. Doing this for every track is overkill. If you're mixing regular pop or rock type music, then if you meter the kick, snare, and possibly the bass instrument, that will get you off to a good enough start that you don't have to bother VUing anything else. That's my opinion, but one example where opinions may, or will, differ is sample based music. If you're making sample based music, then you'll probably source all, or at least some of your samples, from a sample library. What you'll find is that sample library samples tend to be high in level, probably close to maxed-out. This is fine, why waste decibels? But when you import them into your DAW, whether directly or via a sample player instrument, you'll find that when everything is high in level, your mix, well, it won't exactly be uncontrollable, but you're working hard to control it when you should just be making music. So this is where the objective reality of the VU meter can come in. You can set the levels of your sample tracks to 0 VU or thereabouts and then your mix becomes simply a matter of making sweet music. No struggle. I think I heard a question from the back just there. Do I really need a VU meter? Won't the meter in the track work just as well? Aha! You clearly possess a hammer and you've hit this interesting nail right on the head. The meter in the track will work just as well. Because you've controlled the level of the track before the meter and before the fader, the meter will tell you what you want to know. I've said it before and I'll say it again, possibly again and again, bouncing around -18 dBFS, peaking up to around -12 or -10. That will tell you as much as the VU meter can, at least as far as sample levels go. The VU meter can go one stage further though and you might find this useful. The VU meter is a fairly good guide to the subjective loudness of a signal. OK you can hear the subjective loudness subjectively, but this wouldn't be the only area in audio where what you see can support what you hear in your decisions. So, it wouldn't be a thing for everyone, but some will definitely like to assess levels visually as well as orally and for this, a VU on every track probably wouldn't be too much. I'd suggest that you try it. If you like it, then stick with it. If it doesn't seem to give you much benefit, then just keep things simple. That's one approach. You've gain staged your foundation tracks, or perhaps all of your tracks. All of your tracks are bouncing around 0 VU. But there's another way to look at this, and I think that for a lot of people, it could be preferable. It isn't really technical, it isn't really artistic, but it's definitely convenient. It's still a good idea to set your foundation instruments to around 0 VU, or possibly, I could say, your one most foundational instrument, which could easily be the kick drum. Now, don't touch those faders. What you're going to do is, okay, I'm going to have to break my flow here and say that if any track desperately needs help, then do it now. By desperate, I mean a glaring frequency balance issue. Something that you know right from the start you're going to have to fix. Fix it now. Fixed? OK, then start your mix, but not on the faders. Do it with Track Gain. I'm hoping your DAW supports this. If it doesn't, but it has Clip Gain, then use that. Or you can use a trim plugin, one in every track. What you're going to do is get your rough mix together using Track Gain, Clip Gain, or Trim. Don't agonize over this., t doesn't have to be perfect. Just something where the mix makes sense. It shouldn't take you too long. If I said half an hour, that might even be too long, bearing in mind that we each have our preferred pace. Job done. You've just put yourself in the perfect place to start mixing. Everything's sounding good, the song makes sense, all your faders are at zero, ready for your attention. Around zero, by the way, being the place where the fader has its most precise resolution and all of your attention at this point will be musical, because you've done the technical stuff, you've done the convenience stuff. Now you can do the creative stuff, it’s the best part. I'll stress that this is just a possible approach. You don't have to mix like this, but if you give it a try, you might find that you want to mix like this. Mixing During Recording It occurs to me at this point that there's a technique from the old days of analogue that's worth knowing about, perhaps worth trying and will work an awful lot better now with digital equipment than it ever did with analogue. So I said that it can be useful to set levels roughly using track gain, clip gain, or trim plug-ins, so that you start mixing for real with the faders at zero. Well, you can go a stage earlier with this. In the old days of analogue, before it became a thing for tracks to be mixed by a specialist mix engineer, the person who recorded the original tracks, the recording engineer, would also do the mixing, under the supervision of the producer, of course. So you might consider, if you were in this position, that you could be recording a drum kit, perhaps with eight mics. You know that you're going to have to mix it later, because that's part of your job. So why not set the recording levels so that it's already mixed, even though each mic gets recorded to a separate track. It'll save time and effort later. It's one more decision out of the way and with the individual tracks available you can always tweak the balance if necessary. So in other words, make your multitrack recording as though it's mixed already. The levels are baked into your DAW session and you can, as I said, tweak it later. The reason this wasn't more popular in the analogue era is of course that you would inevitably record some tracks at a lower than optimum level, hence the signal to noise ratio wouldn't be so good. But with 24 bit recording, we have masses, absolutely masses of signal to noise ratio to spare. It'll do no harm at all to your recordings to set your levels, as you record, as you want to hear them in your mix. This won't be for everyone, but I do think it's worth a try. I think this is enough to be getting on with for now. Clearly I'm going to need to cover gain staging for plug-ins and I'll do this in the next episode of this podcast series. In the meantime, you can try out the methods I've outlined here and because the DAW is so forgiving, you can add plug-ins anywhere you like, you almost certainly won't go wrong, But as we shall see a little gain staging will help you get the best from your plug-ins. That's it for now. I'm David Mellor, course director of Audio Masterclass. See you in the next episode. Thank-you for listening, and be sure to check out the show notes page for this episode where you'll find further information, along with web links and details of all the other episodes. Oh, and just before you go, let me point you to the soundonsound.com/podcasts website page, where you can explore what's playing on our other channels.