Welcome to part two of the Building Your Own PA blog series. If you missed part one, check it out here. Today we're going to discuss how to choose one of the most important pieces of your PA system - the mixer. Selecting a mixer can seem overwhelming, and there are a lot of decisions to make.
How many channels do you need? Do you want something portable? And should you go with an analogue or digital board? In this post, we’ll demystify the options so you can make an informed decision and select the right mixer for your performance needs.
When you’re looking at a mixer’s specs, it’s natural to focus first on the number of inputs, which is a crucial factor. To figure out how many inputs you need at minimum, start by counting the number of inputs your act requires, including vocal and instrument mics, and DIs. If you plan to mic the drums, assume you’ll need at least four channels for that (kick, snare and two overheads) and probably more. Add all that up, and then figure you’ll need some extra channels in case your band grows or your situation changes in some other way.
But inputs are only part of the story on a mixer. You’ll also want to know the number of subgroups that a mixer has. What’s a sub group? On most mixers, the output of the individual channels is sent by default to the Master Bus, where all the signals are combined and sent to the main output (or outputs). If a mixer has subgroups, you can create sections or groups of your mix (such as vocals or guitars) that is sent to a subgroup before being assigned to the Master output. you’ll have controls that allow you to route the individual input channels to any one of them.
Subgroups are useful in live mixing because you can use them to control selected combinations of inputs with a single fader. Without subgroups, if you wanted to turn all the vocals up, you’d have to raise each individual vocal fader. For example, on a mixer with subgroups, you can assign all your vocals to one subgroup fader, and then you only have to push it up to raise all the vocal channels simultaneously. If you’re going to have someone running sound at your gigs, he or she will have a much easier time with a board that has subgroups.
Another important spec is the number of aux sends. Aux sends allow you to send a copy of the audio from an input channel to a separate “aux output” on the back of the mixer, where you can connect monitors or external effects devices. You can use the aux sends to create separate mixes to send to monitors and to feed multitrack recorders. If you’re using them with outboard effects processors, the output of those devices connects back into the mixer by way of an “aux return” (aka “effects return”) input. The signal is then routed to the mixer’s master out or a sub group. Having more than two aux sends is handy.
Analogue vs. Digital
For simplicity and value, it’s hard to beat an analogue mixer. They tend to be rugged and dependable. And as a rule, they’re considerably cheaper and less complicated to learn to use than digital mixers. Many analogue mixers have a digital component, in that they come with a digital effects section, which allows you to add reverb, delay and other effects. This is convenient, because otherwise, you’ll need to connect separate effects processors.
Despite larger learning curves and higher prices, digital mixers are far superior when it comes to features. The ability to save scenes is especially useful, which enables you to recall the entire state of the mixer at a later time. You could create a preset for every venue you play, which could be recalled the next time you’re there. Or you could create presets for specific songs.
Digital mixers such as the Soundcraft Si Impact provide generally provide more precise EQ, a better selection of effects, built-in compressors on individual channels, automatic feedback suppression and more. Thanks to their DSP power, the higher price of digital mixers is offset somewhat, because you won’t have to allocate money for external effects like you might with an analogue mixer.
Some modern digital mixers can also be controlled from an app on an iPad or Android tablet. This allows you to adjust the mixer while walking around the venue. During soundcheck and the gig itself (especially if you have somebody running sound), tablet control is a useful feature.
You need to balance a lot of different priorities when buying a mixer. Budget, channel count requirements, effects needs, compatibility with any gear you already own, portability, your willingness to deal with the complexity of digital mixers, etc. My advice is to try to get a mixer that exceeds your needs by some degree, so you have room to grow. Also, stick with established brands that you can rely on for good sound and good service—and that you know will be around for years to come.
Don’t miss part three of this series to learn how to select the right speakers for your personal PA system! What are you looking for in a mixer? Let us know in the comments.
First published in the HARMAN Insights Blog by Mike Levine, former editor of Electronic Musician. Mike has written numerous articles on music technology and recording.