Analog Summing vs Digital Summing

Hey folks. Matthew Weiss here — weiss-sound.com, theproaudiofiles.com, and mixthru.co.

Welcome to the Ask Weiss series, and this question is a general purpose question that I’ve seen floating about on forums and everything like that, and that is, “What are the merits to analog summing versus digital summing, and is analog summing better?”

Okay, so we have to understand that when we’re making this comparison, it’s not exactly the same thing. It’s almost apples to apples, but not quite. A digital summation is literally a sum. You are taking words, which are data points, and you are adding them together, functionally.

So it is literally a sum of amplitude points being reconstructed into a new function.

That’s it. It’s one-to-one.

In analog summing, it’s not quite the same, because you have multiple voltage sources coming together, which is going to change your impedance, it’s going to have to go to a source which is going to have a nominal operating voltage level, and you’re going to end up overloading that if you don’t put resistors in the path.

On top of that, if the voltage changes, if there’s dramatic changes, you’re going to get impedance shifts along the way, meaning your impedance matching is never going to be spot on, it’s always going to be changing whether or not the kick drum is hitting or something, so you might want to have some sort of regulatory system involved.

So it’s not really as clean as, “Yeah, we’re just putting all of the stuff together,” now you have to do it through some kind of a mechanism.

So before there was any kind of digital recording systems, the analog recording systems were striving to get close to what is called a one-to-one transfer, which is what you get in is what you get out. Ideally, they would be exactly the same.

Now of course, you can’t get there because physical limitations exist in the world. But people get better and better, technology develops, and you get something that is closer to that.

But now, we have digital summing. We have a perfect one-to-one transfer. So the goal of analog summing has changed, because if you want that, we already have it. So now, when people are looking at analog summing, what they’re really looking at is the non-linearities that come about as a result of a process, and the benefit to those non-linearities, and in a way, it kind of means that the worse the summing mixer is, the better it is.

Okay, but anyway, that’s all talk and hearsay and etcetera etcetera.

Let me just show you some examples, and we’ll pull them apart real quick, and I’ll leave it at that. So this is my dry mix. This was summed digitally, and I’m going to play it for you.

[mix digitally summed]

And this was summed through my Unit Audio MicroUnit here, and the makeup gain is going through my Avalon M5s.

So, here we go.

[mix analog summed]

I’m going to A/B them real quick one more time, and I’m just going to pull apart the differences that I’m hearing.

[mix plays, switching between digital and analog summed]

So these are about level matched. They’re pretty darn close. I was working with some null tests to get it about as even as possible, but there are a few things that fundamentally changed that make it impossible to null.

So the first thing that I notice is that the digital sum to me actually sounds bigger. It has a larger scope of sound.

The summed signal immediately has an interesting and compelling vibe to it that I do like, so I don’t think I’m getting a bigger, wider, taller mix when I sum something. What I think I’m getting is an interesting color that seems to exist over the entire mix in a really nice way.

The other thing that’s worth pointing out is the frequency response has changed. There is a very tiny bit of attenuation going on in the deeper part of the low end, maybe around 60Hz, and there’s a pretty notable wide roll-off coming in from the top end.

So we’re losing a very little bit of low end, and a pretty good amount of high end. So I’m going to A/B that again real quick.

[song plays, switching between digital and analog summed]

Right. Now, is that a problem? It can be, but it can also really be a moot point, because I have an equalizer. I can simply boost up some top end and boost up a little bit of the bottom end, and rebalance it.

[analog sum, EQ’d]

So, before…

[song, before]

After.

[song after]

So, the two things to point out are one, this is not an exact comparison, because it’s not an exact science. It’s art.

So, did I match the frequency curves perfectly? No. Is that really even possible? No. Plus, the saturation is going to affect our perception of the frequency as well, so you know, the question is just ultimately, I just have to go with my gut and what I like. In this particular case, I happen to like the saturated signal with a little bit of EQ to balance it out. I feel like it has an enriched quality, and that enriched quality helps to give it a sense of depth that I don’t feel it had without it.

But that said, I stand by both mixes. I think my dry mix sounds good, and so this is not something where suddenly I fixed the problems with digital mixing. No, there’s no problem. It already sounds good, even without this kind of processing.

This is just a bit of icing on the cake, and I do feel like it is beneficial in this circumstance. Maybe it wouldn’t be in others, and so, I think that pretty much settles the debate. It horses for courses, and a comparison will quickly reveal that the changes are not that dramatic, and they’re simply a matter of taste.

Alright guys, until next time.

Matthew Weiss

Matthew Weiss

Matthew Weiss is a Grammy nominated and Spellemann Award winning audio engineer from Philadelphia. Matthew has mixed songs for Snoop, Sonny Digital, Gorilla Zoe, Uri Caine, Dizzee Rascal, Arrested Development, 9th Wonder, !llmind & more. Get in touch: Weiss-Sound.com.
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