Signal Flow Part 2

As developed in last week’s Signal Flow Part 1 [June 2013], Audio Engineering is an enjoyable technical and creative pursuit. It is dependent upon the engineer understanding the fundamentals. Signal Flow is one of the core fundamentals. Understanding and practicing these three stages of Signal Flow until committed to muscle memory is essential to the development of the aspiring engineer.
This week we will build upon the three stages of Signal Flow to Part 2, including Stage 4 and Stage 5.
Note: On a console that is designed primarily for recording/tracking, such as Neve C75 or a Behringer Erodes SX4882, the Channel Path will by default be routed via the large/primary faders, and the Monitor Path will by default be routed via the small/Mix B faders or pots.
In contrast: On a console that is designed primarily for mixing, such as a Audient ASP8024 or a ASP4816, the Channel Path will by default be routed via the small/secondary faders, and the Monitor Path will by default be routed via the large/primary faders.
Of course, one of the advantages of an in-line console is to have the flexibility in routing options and being able to switch what Path is routed to the faders as the need desires. Therefore, my reference to the Channel and Monitor Path and their respective faders are based  on a console that is designed primarily for recording/tracking.

Audio Processing

Before we proceed to Stage 4 of Signal Flow, lets add some external processing into Stage 2 of the Recording process. In the Audio Industry there are accepted ways to route specific types of audio processing when using external audio processing hardware. 
Audio Industry 8 Channel Studio Signal Flow.P10
The industry standard is to route signal from either the Insert Send/Return within a Channel strip, or via the Auxiliary Send/Returns across a number of Channel strips. In circumstances where we only want to process the signal for one particular channel, we would use Insert Send/Returns. This is usually the case when we want to apply Spectral or Dynamic processing to a particular signal such as an individual instrument. For instances when we want to apply particular processing across a number of Channels or instruments, then we use the Auxilliairies Send/Returns.
Firstly we must Send the raw signal from the Channel strip or strips (referred to as dry signal) to the external audio processing hardware.

Audio Industry 8 Channel Studio Signal Flow.P11

 Once we have processed the signal (referred to as wet signal), we must return the processed signal back to the particular Channel strip or strips on the console.

Audio Industry 8 Channel Studio Signal Flow.P13

We now have added processing to either one or a number of the Channel strips on the console, within Stage 2 of the Recording process. Before we proceed, let’s recap on the Signal Flow.

Audio Engineering Signal Flow

Recording phase – Stage 1,2,3: 

Last week in Audio Signal Flow stage one, two and three, I introduced the capturing of a sound source, routing the signal to the console, monitoring that sound source pre-tape (Channel Path), taking this signal to tape, recording it on the multi-track-recorder (MTR), and then returning the signal back to the console where we had the opportunity to monitor the signal one more time post-tape (Monitor Path).
Being able to monitor the path at both pre-tape and post-tape allows the engineer to check all stages of the signal flow to ensure that there is good signal, at good levels (not too low or not too high), no extraneous sounds (such as noise, hum, buzz, crackle, hiss, etc) that could be a problem if we were to discover such once we have completed the recording phase. Once we have successfully captured and recorded the sound source to the MTR (Recording phase), we need to progress to the next phase, Mixing as part of Post-Production process

Mixing phase – Stage 3, 4, 5: 

Stage 3:

In the mixing phase, traditionally completed by a specialist engineer other than the recording engineer, the recorded tracks are routed from the tape back to the console. This stage equates to Stage three of the Recording phase, but perhaps with a more focussed intention. The purpose of this stage is to commence mixing the various tracks of audio into a blended organise song with both corrective and creative processing applied. The fundamentals as available on most analogue consoles, include manipulating the gain levels, the stereo field via panning, and the spectral qualities via the equalisation and filters on the console. Once we are satisfied a balanced mix of all of the instruments within the mix has been achieved, we need to capture this mix onto tape to be able to play it back at anytime in the future.

Stage 4:

In the fourth stage – Stage 4 Signal Flow, the multiple signals are routed from the console to a device that is capable of recording this summed balanced and processed signal into a single stereo track. This mix of the multiple channels is referred to as a Stereo Mix.

Audio Industry 8 Channel Studio Signal Flow.P14

In order to do this, we route the signal from the console’s Master fader send…….
Audio Industry 8 Channel Studio Signal Flow.P16
… to the DAW via a AD/DA interface (for example Stereo Input 1+2)..
[Note: If the Studio has a patchbay setup, you are more than likely in need of routing this Stage 4 Signal Flow via that patchbay].

Audio Industry 8 Channel Studio Signal Flow.P18

This completes Stage four, from the console to the MTR.

Stage 5:

Once we have done this, we need to prepare to Return the signal back to the console for Monitoring the Stereo Mix track. This is Stage 5 of the Mixing phase. So how do we do Return the signal to the console for monitoring this Stereo Mix track?
You will note the Outputs in the tape are already being used, returning the signal of the original mix to the console’s Channel Strips (Stage 3 Monitoring Path) in order for us to monitor the original mix. So, we need an alternate way to route this Stereo Mix track Return back to the console, in order to monitor and confirm this final Stereo Mix track meets our technical and creative standards.
Whilst each studio will have its own particular routing and naming protocol, most consoles have what we refer to as a 2-Track monitoring function. 2-Track monitoring refers to the monitoring of the final Stereo Mix track Return – Stage 5 of the Mixing phase. As the mono outputs are occupied by Stage 3, we need an alternative routing option from the DAW via the AD/DA interface. This is usually done via a digital output such as an ADAT or a SPIDF output.
[Note: Before we leave the DAW, we need to confirm the Stereo Mix levels in the virtual MTR are appropriate via Input Monitoring. If the levels are not appropriate (too high or too low), you need to re-check your mix levels, and adjust accordingly]. 

Audio Industry 8 Channel Studio Signal Flow.P20

In order to monitor this Stereo Mix track signal on the console, you need to select the 2-Track function on the console, in order to monitor this final Stereo Mix track Return – Stage 5 of the Mixing phase.
[Note: each console manufacturer is likely to have their own naming protocol for this 2-Track monitoring function. For example, a number of more recent consoles refer to this final Stereo Mix monitoring function as DAW].

Audio Industry 8 Channel Studio Signal Flow.P21

Selecting this 2-Track function on the console, will route the Stereo Mix signal to the monitors for confirming the technical and creative merits of your final Stereo Mix. To confirm that you as the Mixing Engineer is actually monitoring Stage 5 (and not Stage 3), if you select the mute button on the Stereo Mix track within the DAW, the monitoring signal to the Control Room monitors should be cut. Deselect the mute button to continue to monitor this Stereo Mix signal.

Audio Industry 8 Channel Studio Signal Flow.P22

This completes the 3 stages of the Mixing phase – Stage 3, Stage 4 and Stage 5.
Audio Engineering is an enjoyable, technical and creative pursuit. It is dependent upon the engineer understanding the fundamentals. Signal Flow is one of the core fundamentals. Understanding and practicing these three stages of the Recording phase’ Signal Flow and the three stages of the Mixing phase Signal Flow until committed to muscle memory is essential to the development of the aspiring engineer.
Reference
Images courtesy of:  David L Page  Accessed 3rd June, 2013
– ©David L Page 10/06/2013
– updated ©David L Page 14/02/2016
Copyright: No aspect of the content of this blog or blog site is to be reprinted or used within any practice without strict permission directly from David L Page.
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