(A big thanks to reader Daniel McGinn for the prompt to write about this topic.)
A sound quality problem had been plaguing me since I had begun playing guitar with Ableton Live - how do you plug in your guitar to Ableton, and then run it out to a guitar amp? The answer to this can be deceptively simple - if you have the right type of amplifier.
The common mistake people make here has to do with what I would call "double-amping" your guitar signal. Normally when plugging in your guitar and playing traditionally without a computer in the signal chain, you would run cable from your Guitar Output to your Effects Pedals, and finally to your Amp Input, so the signal goes through the Amplifier's Pre-Amp. If you don't know what a Pre-Amp is, for our uses here all you need to know is that it adjusts parameters like the Pre- and Post-Input Gain (basically how hot and loud the signal should be), as well as Low-Mid-High EQ values before handing it off to the Amplifier so the signal can be, well, amplified.
The problem with this approach when working with Ableton in the signal chain is that many of the effects you add such as Ableton's own Amp and Cabinet Audio Effects will also Pre-Amp your signal. Hence, the afore-mentioned "double-amping." So what does double-amping sound like, then? Well you will have a considerable amount of line level noise - this can sound like static, hiss and hum. Also, your more clean sounding effects presets will sound slightly dirtier or overdriven, and your monster tones like overdrive and distortion will sound downright filthy and hard to control, and will be prone to instant feedback. So, if it is truly bad for your tone to double amp your signal, where else can your plug your guitar into your amplifier?
Not all amps are created equal. Many do not have the crucial ingredient for this setup: an Effects Loop with dedicated “Effects Send” and “Effects Return” jacks on the back of the amp. The Effects Loop feature is usually featured on larger, high-end combo amps and heads/cabinet setups, and they are traditionally meant for non-tone shaping, time based effects like reverbs/delays/phasers/flangers, etc. If you cannot find them on the front panel of the amp next to the standard input jack, you can usually find them on the back of the amplifier next to other jacks such as monitor and headphone outputs, and so forth. Here is my rule of thumb - while you should place your tone-shaping compressors/overdrives/distortion pedals before the Amplifier input so the pre-amp can sum them all in and then amp the signal, all the time-based effects usually come later in the signal chain after the Pre-Amp when possible. Many players do not have an Effects Loop, so they simply place time-based effects after the Overdrive/Distortion/Compression but before the Amplifier Input. Obviously, the order of your signal chain is up to you - you can achieve different sounds and very creative effects simply by moving items in the chain around in a different order, so there is no "right" way - but the focus here is to start you off with the neatest uncolored tone so that Ableton and other Audio Plug-ins in your computer can act on the cleanest tone possible before handing it back to the Audio Interface to be passed on to your Amplifier. That being said, if you don’t have an Effects Loop on your Amp, this article will probably not help you much.
What I have found is that I get much better tone across the spectrum of subtle and soft vibes, to warm and creamy overdrives, shrill distortions, smooth delays and reverbs if I am sure to run my guitar into the audio interface, through Ableton, back out into the audio interface, then finally into the Effects Return jack of the amplifier, skipping the Amplifier Input (and thus the Pre-Amp). I then adjust the overall volume of the Guitar Amp and leave Reverb off, as I can handle that within Ableton Live.
The way I personally choose to do this, I avoid analog pedals entirely (this might be a deal breaker for you if you need or want to use them). I use Native Instruments Guitar Rig Pro 5 to process my entire sound from tone shaping to time-based effects. This is because Guitar Rig works in “presets” and it would be very laborious to strip out all the tone shaping from the effects chain of each preset to avoid double-amping. Guitar Rig is basically a virtual amp head, and your combo or stack amp also has it's own physical amp head already acting on the signal. As I said before, if you use tone-shaping and emulation tools to sound like an Amp or Custom setup, and then run it into the standard input of an Amp you are then double-amping and the guitar will feedback and misbehave. Going into the Effects Loop Return jack means you are using the amplifier solely as a loudspeaker, not to process the sound at all.
If you have tried both ways, you will be amazed how much better it sounds. If you have a combo amp without an FX SEND and RETURN (i.e. a head and amp in one body), you might be out of luck - although many have it. If you have a head and separate cabinet you will almost for sure have this capability. You should not need a D.I. Box for this, but it depends on the electricity coming out of the walls where you are trying to play. Might be a good idea to try adding one between the Guitar and Audio Interface if the above setup still has lots of noise to it for you.
If you do have a lot of analog pedal gear that you just cannot imagine abandoning, I’ll just say I would be a bit nervous about running tone based stuff pre-Ableton, then doing more tone shaping stuff in Ableton as well. You might end up double-amping there as well - so what you could do is choose one or the other - either shape your tone totally pre-Ableton signal-wise and use Ableton only for time-based and sound coloring effects, or let it all be done in Ableton and Guitar Rig or your plugin of choice (prob a cleaner result). I suppose you could also place analog hardware time-based effects after your audio interface but before your Effects Return Jack on the Amp, but I have not tried it personally. Give it a shot! I did all of this through a Peavey Classic 30 Tweed and a Marshall JCM 2000 DSL 401 and they both kicked ass. I was dialing up tones from Buddy Guy to Radiohead in no time with Guitar Rig and switching presets in real time using a Rig Control 3 or Looptimus Midi Foot Pedal.
Best of luck! Let me know how it goes in the comments or on Twitter.