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If I am digitally capturing an audio signal from an analog source and I know I will want some analog effects applied, is it better to use them on the analog signal before doing the ADC, or should I opt for as clean as a digital signal as possible and then pass that signal through the both the analog and digital effects I may need?

I assume that using the digital effects on the analog signal is unnecessary (in terms of quality of the final signal after all effects), so I can do them once digitized to my hearts content without as much loss. But also open to thoughts here.

I know that when the analog effects are applied before recording, they are "destructive" edits to the signal - meaning there is no going back. So you may not want to do it for that reason. However I had always thought that any analog work you're sure of should be done first (before ADC is done) because an analog signal is much more detailed or higher resolution before being digitized. By applying several analog effects on the analog signal, I had assumed the resulting final signal would have a similar detail / resolution as the input (within reason). Conversely, after digitizing where the signal goes through a "best fit" process to find the corresponding digital representation, I feared there would be a sort of "rounding error" that can add up since we're applying filters to a digital signal that is lossy.

I brought this up to an electrical engineer and he fought me on it so much I was left very confused. His argument was that the clean digital signal was the best for more reasons than just convenience.

Is there any (noticeable) difference to the signal if I apply analog effects before ADC rather than after or is it just theoretical?

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    $\begingroup$ Your expert friend has a correct expert experience. His argument is valid, and you signal knowledge of that argument from the start of your question. What do you expect us to change? $\endgroup$
    – Marcus Müller
    Jul 21, 2021 at 19:35
  • $\begingroup$ Hmmm, I don't understand why it is preferred to record a clean signal first, then perform D/A conversion, apply the analog effects, and then A/D convert. Is this based on convenience reasons (which I totally get) or theoretical considerations for the optimum audio quality? In the latter case, I'd assume processing the effects in the original, analog, domain should be preferred because we save two conversion operations, each of them introducing artifacts. I agree, however, that these will usually be inaudible. $\endgroup$
    – applesoup
    Jul 28, 2021 at 21:54
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    $\begingroup$ @applesoup Yeah, that was my original thesis. My take away from these answers is that there is absolutely no way multiple A/D D/A round trips could be as high quality and pure analog, but for most people it's a combination of convenience reasons coupled with the "better" way being an inaudible improvement so why bother $\endgroup$
    – hamburgermenu
    Jul 29, 2021 at 11:29

2 Answers 2

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It depends and typically there are more important aspects to consider:

  1. Make sure your effects are in the right order. I'm guessing you do NOT want a reverb before your distortion pedal regardless of whether any of these is analog or digital.
  2. Some effects must be part of the recording and cannot easily be applied through post-processing. For example if you want a screaming guitar with pinched harmonics and amplifier feedback, you need do this at recording time since you need to adjust your playing to the way the effect and the amp reacts to your fingers (and how you hold and handle the guitar): the effect becomes part of the instrument.

In most cases it's best to start with a clean digital recording and apply the effects later in the correct order. Analog effects can always be applied through an effects loop or insert if needed. If you have decent A/D and D/A to signal quality loss is negligible.

In a few cases, the effect needs to be part of the actual recording, i.e. it's applied first. Again, this doesn't depend on whether this effect is analog or digital.

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We're still a couple steps behind on emulating good tube distortion and even some other effects you find in some stomp boxes (although a lotta stomps have digital innards).

Don't you have multitrack recording? Why not record both the clean guitar as well as the great-sounding guitar coming outa the Mesa Boogie?

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