Signal Flow Part 1
This article was written orginally for the blog at Carvin Amps and Audio. I repost it here, and encourage you to check out Carvin’s amazing line of products!
Signal flow – the direction audio signal “travels” in a live or recording setup – is the most fundamental concept in audio, and understanding it is a prerequisite to understanding anything else in audio.
Still, there are places even veterans can get tripped up, so here we’ll get back to basics and discuss signal flow from a true beginner’s perspective. We’ll start in the recording studio to get a solid foundation.
Signal flow fundamentals
When it comes to studios, many setups these days are minimal when it comes to actual, physical audio connections. Still, understanding signal flow at its most basic is the quickest way to understanding the complexities in digital audio workstations (DAWs) and other audio software.
In addition, live sound setups are still physical entities, and in that setting, certain concepts such as feedback are crucial to understand.
So, to begin with, we can easily understand signal flow if we think of sound itself as directional. As we all know, sound is simply a phenomenon of air molecules being “pushed” out by something – a voice, a drum, whatever. We “hear” sound by detecting variances in how those molecules propagate through the air and arrive in our ear.
Sound actually radiates in all directions, but to understand signal flow, we can temporarily think of sound as going in one direction – from the source to the receiver.
A source creates sound. A drum is a source. A receiver receives sound. Your ear is a receiver.
Everything else in signal flow follows from here.
In audio, we need to turn sound into an electrical signal before it can be amplified or recorded, but once we do that, the concept is the same. Audio “travels” in one direction – from source to receiver.
This fundamental understanding will make the rest much easier.
Let’s look at two simple, typical situations, both involving a singer.
Situation 1: Singer sings into a microphone which is recorded to a recording device (doesn’t matter what kind). First the sound wave travels from singer to microphone. Then it’s converted to signal and it travels from the microphone to a preamp, then into the recorder. This is the signal flow:
- Recording device input
Situation 2: Singer listens back to recording. First the recorder plays back an audio signal, which travels to an amplifier, then to a speaker. The speaker converts the audio signal back into a sound wave, which travels to the singer’s ears. Here is the signal flow:
- Recording device output
Signal flow is really that simple! But let’s make it slightly more complicated, so we’re never confused by the audio gear itself. Revisiting our two scenarios, we actually have:
Situation 1 – Singer records some singing:
- Singer output (aka mouth) to
- Mic input (mic itself) to
- Mic output (XLR plug and cable) to
- Pre-amp input to
- Pre-amp output to
- Recording device input to
- Recording media (tape, hard drive, etc)
Situation 2: Singer listens to recording
- Recording device output to
- Amplifier input to
- Amplifier output to
- Speaker input
- Speaker output (aka actual speaker moving air)
- Human input (aka ears)
The reason to understand it this way is to understand that every audio device has an input and an output. Signal always flows from the “output” of one device to the “input” of another, and then to the “output” of the second device, and so on:
It doesn’t matter how many devices there are, this is always how signal flows.
The real world is obviously more complicated than the situations above, but once you understand that signal simply goes in one direction, everything follows. In situation 2 above, it would be more likely that the signal goes through another step before the amplifier – a mixer.
A big 56 channel monster console looks intimidating with its hundreds of knobs and buttons, but it’s actually just the same thing – a channel strip – repeated over and over. And there’s an easy way to remember which way signal flows in a channel strip. Think of tipping the mixer toward you so that it sits vertically. Signal flows from top to bottom. Let’s pick a random channel…say 12, on a typical analog console. Signal flow on channel twelve is:
- Channel 12 input
- Channel 12 gain
- Channel 12 EQ section
- Channel 12 pan
- Channel 12 fader
After the channel fader, audio goes to the master fader and then to the mixer’s outputs, and finally to the amplifier and speakers.
That’s it. Channels 1-11 and 13-whatever all work the same way.
Now that we’ve laid the groundwork, we know that signal flows the same way in a digital world as it does in the analog audio world. There are complications, but few that aren’t also available in analog audio. We’ll get into some of those more advanced topics in an upcoming article.
For now, we can think of the digital audio workstation (DAW) as a fancy recording device and mixer in one. In digital recording, the basic signal chain described above is the same, with the addition of an audio interface and/or audio to digital convertor (ADC), to turn analog audio signal into digital information:
- Audio interface/ADC*
* ADCs, DACs (digital to audio converters) and audio interfaces are two separate entities, but they’re typically combined in one device.
To listen back, the chain would employ a DAC and the flow would look like this:
- DAC/Audio interface
As mentioned above, you might include a mixer in that series – or not. And to make things more complicated, DAWs have their own internal mixers (usually). As you might expect, signal flow in a DAW works similarly to a mixer – but because you’re in a digital domain, there are many more options.
In part 2, we’ll cover those options and a host of real-world signal flow issues such as splitting, inserts, sends, bussing, monitoring, plugins, and live audio considerations like feedback.
If you have questions or want to talk, just hit me up on Facebook @AaronJTrumm – or email me aaron @ aarontrumm.com