If you are taking the Intro to Music Production course through coursera.org, please skip to the next paragraph. If you are not, here is a quick debriefing on what this blog post is all about : ) I enrolled in the aforementioned production course online (it’s free, by the way, so you might want to check it out for yourself) and part of the evaluation process involves us having to re-teach an element of the coursework. Since this information might be useful to other people, I thought I’d post these assignments on my blog. That being said, I am a student (not an expert), so don’t take what I say here as the ultimate truth. In fact, if you have other insights that might enhance or correct my understanding of the content, I’d love for you to leave a comment at the bottom of the post : )

What is “Signal Flow”?

In short, Signal flow is the path an audio signal takes from a sound source, such as your voice (which creates pressure variations in the air) or an electric guitar (which creates sound through the vibration of its strings), to a new output (such as speakers at a music venue, your practice amp at home, or an MP3 after you’ve recorded a song on your computer).

What is a “Channel Strip”?

Channel strips are used to integrate audio signals into a sound system (ie., live show PA systems) or recording (usually via an audio interface that connects to your computer’s Digital Audio Workstation).

What does this have to do with a Mixing Board?

While channel strips can be purchased as stand alone devices, if you’re recording at home or doing sound for a gig at your local pub, you’re probably going to be using a mixing board , audio interface, or console that has one or more channel strips. The more channel strips you have, the more sounds you can have going through your system at the same time and the more control you’ll have over the overall “mix” of all those sounds. For example, if you are recording a drum kit, you can use one room mic (only one channel required) and you will capture the sound of that drum kit as that microphone hears it from that particular position in the room. But, if you have a mixing board and a set of drum mics that you can place in a variety of positions around the kit and room, you can record each individual drum with more clarity. That, in turn, provides you with more opportunities to shape the character and presentation of the individual and overall drum sounds.

How Signal Flows through the Channel Strip of a Soundcraft EPM8 Mixing Board

In most mixing boards (like the Soundcraft EPM8) the direction of signal flow is from top to bottom and will flow through the various controls in this order:

1) XLR Input or 2) Line Input

XLR inputs are typically used for microphones and it is at this stage that the channel strip takes low level audio signals (ex: from a microphone or pick up) and brings that signal up to line level via a pre amp so that the sound can be better heard and manipulated in/through your system.

Line inputs are designed for signals that are already at line level (synths, drum machines, DIs). If your board says “balanced or unbalanced”, it can take both TS or TRS cables. Though it doesn’t say directly next to the input on this board, there are instructions on the back and in the user manual explaining that the line inputs on the EPM8 are designed for balanced/TRS cables, but that TS cables can be used if you rewire the cable itself using the instructions they have provided (probably easier, and less likely to create electrical noise and/or hazards, to just buy a balanced cable :).

Because there are no Hi-Z or “instrument” inputs (which are used to plug guitars and other instruments with pick ups directly into a channel), it is best to first connect your guitar to a DI box and then connect the DI to the Line Input. A little more explanation between the different types of inputs and why you use them can be found here.

3) Inserts

Inserts are where you connect signal processors such as gates and compressors. The signal is sent out to  the effect pedal/processor and then sent back to the channel through a special Y shaped “insert cable” (which are required for this function to work properly).

Based on my understanding from Louden’s lesson, most channel strips have inserts after the trim/gain knob and on the back of the board. The EPM8, however, has the insert function physically located before the trim and on the front.

4) Trim / Gain

While there are technical differences between “trim” and “gain”, many manufacturers label this knob using either term. On the EPM8 it is called “gain”. Either way, at this stage in the signal flow, this particular knob is used to increase or decrease the level of the incoming signal.

5) EQ Stage

The EQ stage on the EPM8 consists of 4 knobs for fine tuning the quality or timbre of the audio signal through equalizing filters.

Based on my understanding from Louden’s lesson, most channel strips have the EQ stage after the Aux sends. The EPM8, however, has the EQ stage physically located before the aux sends.

6) Aux Sends

Auxiliary sends are used to change the level of that channel’s signal to an artist’s monitors
(such as headphones and in-ear or stage monitors). This is useful, as different artists have difference preferences and take cues from different instruments which they may want to hear higher in the mix while tracking or performing. With the EPM8, Aux 1 is switchable pre/post fade. Meaning, that you can choose whether the artist receives the natural level of the audio signal (pre fade) or the altered level (post fade).

7) Pan

The pan knob controls the amount of signal gong to the left and right channel of the Mix Bus (step 10), which in turns affects how much of that particular channel’s sound will be heard by the listener’s left or right ear (especially in the case of headphones). Do not be confused: panning does not move the signal from left to right and vice versa, it simply increases or decreases the amount of that signal to those particular locations.

8) Mute, Solo, and PFL

Pressing the mute button will silence that track. If your board has a solo button, it will allow only the signal from that channel to be go through (some boards allow you to solo multiple tracks at the same time). The EPM8 does not have a solo button, but it does have a PFL which is used to monitor the post-eq / pre-fader signal from that channel in the main meter or your monitors. This functions in a ‘solo’ way, where only that signal will go to the meter and monitor (unless you select PFL for multiple tracks at the same time), but it will not affect the master mix output like the mute or solo buttons do.

9) Fader

The fader controls the final audio signal level from that channel, which is then sent to the Master Bus (called the “Mix Bus” on the EPM8) where it is mixed with the signals from the rest of the channels. A zero (on the EPM8) or “u” for “unity” will be present and represents zero change in gain. This is ideal for capturing the true signal, as it means all your devices (pre amp, instrument, etc.) are calibrated and communicating with each other effectively. Arguments for why one should strive to mix live at unity are here.

10) Mix Faders

The Mix or “Master” faders control the overall level of the mix outputs (what the audience will hear at the show or what the tracks will sound like after you record them together).

11) Main Meters

The main meters help you visualize the sound coming from the mix bus (and controlled by the master faders). Ideally, when recording, you want to set the overall level so that the performance is mainly in the green and peaks in the yellow zones. For live performance you can go higher, if necessary, but in either case, stay out of the red (where the sound you have so carefully channeled will clip and/or distort).