Pro Audio Files

Analog vs Digital Summing: Which is Preferred?

When it comes to combining audio in a multitrack recording, there are two categories of methods: digital summing and analog summing.

Digital summing is accomplished within the software of a Digital Audio Workstation (DAW). Analog summing is accomplished using external hardware to the DAW.

Even if the input audio is identical when using digital and analog summing, the output signals will be different. The question then becomes, “can listeners perceive the difference?” Ian Vargo recently conducted an experiment to answer this question. The answer is revealed in the comments — scroller beware.

Preference Experiment

When it comes to summing, a slightly different question to ask is whether listeners have a preference for analog or digital summing. In general, detection tests (can you hear a difference?) answer a different question than preference tests (do you like one option more than another?).

I’ve been teaching a class at Belmont University that covers topics including perceptual experiments, the scientific method, and the auditory system. As part of the class, one group of students conducted an experiment on listener preferences for analog and digital summing.

An additional question they asked as part of the experiment was whether the genre of music influences preferences for summing type. The results of the experiment were presented and published as part of the 137th AES Conference.

To create the sound files for the experiment, digital summing was accomplished within Pro Tools. Analog summing was accomplished using an ADM 780 console. The digital instrument stems were converted to analog separately using a Focusrite Rednet interface. After analog summing using the console, the stereo audio signal was converted back to digital using the same interface.

During the listening experiment, each listener heard digital and analog sound files without knowing which was which. Each listener had to respond by picking which file they preferred for a repeated number of trials. This was done with sound files for three separate genres: classical, pop/country, and hard rock.

Results

The results of the experiment indicated that listeners did show a preference for specific summing types.

  • For the files representing classical music, listeners preferred digital summing.
  • For the files representing hard rock, listeners preferred analog summing.
  • For the files representing pop/country, listeners did not show a preference for either type of summing.

These results suggest that listeners do not always prefer the same type of summing in all cases. In fact, a listener’s preference for summing type depends on the genre of music. In some cases digital summing is preferred. In other cases, analog is preferred.

Conclusion

As an audio engineer, you have a choice to make between analog and digital summing. At the end of the day, your choice should be based on what sounds best. This experiment provides some insight to determining which type of summing listeners prefer.

If you cannot afford to use true analog summing or do not like the workflow, there are plenty of digital plugins that model the processing of analog summing. Using processors to achieve an “analog” sound can sometimes improve the sound of your recordings, but of course should not be overused to the point of making the recording sound worse.

Check out the actual journal article for a detailed explanation of the experiment.

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Eric Tarr

Eric Tarr

Eric Tarr is a musician, audio engineer, and producer based in Columbus, Ohio. Currently a Professor of Audio Engineering Technology at Belmont University in Nashville, TN.
  • Mad-D

    Great!

  • Pete Woj

    Great article, Eric! Love the idea and the test 🙂 Im inclined to agree with you. I have a Dangerous Analog Summing rig that I use often, but its not always the right option for me. In every session I mix I have 2 print tracks set up labeled “ITB” and “OTB”. One I print from my MixBuss and the other I print from the “Sum In” on my Dangerous rig. I A/B them heavily before deciding which is the right mix to use/send out. The one thing I do find extremely helpful about summing out of the box is the extra headroom I get when printing. If I have a super large or busy mix where gain staging is tougher to control than usual, I’ll sum out of the box every time just for the added headroom I get on the round trip back in. Anywho, thanks for the article, Eric! Awesome stuff as usual 🙂

  • MikeQuinn

    Excellent! Before reading my assumption was that it would depend upon the music genre and that was the conclusion. Would I be correct in thinking Jazz would be best using analogue?

  • Tite Trax

    Makes sense to me. Classical music has such a wide dynamic range that analog “noise” would be evident in musical passages with low volume levels, so digital would be preferable to analog here. Hard Rock is almost always loud and “overdriven”, so the coloration you get from overdriving analog is preferable to digital here since the music is too loud to hear analog “noise”. Pop/Country’s dynamic range is somewhere BETWEEN the other two genres so there was no preference indicated here. Yeah, makes sense to me.

  • Robert Weber

    I’ve heard some mixers say that this sort of comparison is flawed because a mixer will make different decisions depending on whether they are monitoring a analog or digitally summed mix while working on it. Pete – any you’re the only one so far who has tried both – any truth to that?

    Mike Quinn – I would expect Jazz would fall along the same lines as classical for similar reasons. Unless it’s a kickin’ big band extravaganza, there would likely be enough variation in the dynamics to play havoc with analog’s noise floor.

  • Thanks for the Cliff notes man!

  • Freddy Phitness

    Interesting, would be curious to know what people would say for other genres, especially for a few electronic music styles… =)

  • ThereIveSaidIt

    Could it be that people have innate ideas about what rock should sound like, and this common preference was formed over the golden years of rock music (60’s and 70’s) in which everything was analog? In contrast, there are no “classic” classical recordings – at least not in the ears of the masses – and thus there is no set idea of what classical music should sound like. So it could be that in the absence such preconceived opinion, the cleaner sound is preferred.

    Also, I’d like to see the results broken down in terms of age. It would be interesting to see if younger people have a different preference due to the fact of them having been raised with music mixed ITB.

    • Dennis Bajer

      In the AES article it says:
      “Twenty-one subjects participated as listeners in the perceptual experiment. Subjects were undergraduate students at Belmont University in Nashville, TN; ranging in age from 20 to 23 years old. Subjects had received a minimum of three years of formal critical listening training.”

      it also says:
      “Across all musical genres, compiled group responses indicated no significant preference for summing type.”

      I find it very hard to say that there is a genre-specific preference when you’re study is based on 21 people…

  • Albert Kaugh

    It’s critical to note that digital summing design can vary hugely from one system to the next. For instance, one of the most sophisticated and expensive DAWs on the planet (which I shall not name, but is very DSD-friendly) has really poor digital summing. Mixes on this DAW sound pinched and smallish and even subtly granular when pushed. And yet some of the most common mix engines I’ve used sound superb, including Sonar, Magix Samplitude / Sequoia, Reaper, and Ableton Live.

  • lysdexic

    what about genres that are actually relevant in 2015? who’s mixing classical or country records in your readership?

  • Kevin Kelly

    While a good starting point study, to assume that all analog summing systems are created equal and to use an atypical prototype (the ADM console) to “represent” all analog summing, makes me want to know how other popular summing rigs would have measured up to the Pro Tools digital 2-buss. The Dangerous active system sounds pretty different to me than passive summing into a pair of Grace/Neve/API preamps for example. Also, the discussion doesn’t really boil down to “do you like A or B”. If you sum in the analog domain you can more easily take advantage of analog hardware coloration without suffering additional conversions. Now the incentive for the analog summing has an additional objective. (by the way, I love the ADM gear, I’m just saying it’s not the most common analog summing solution).

  • The consumer listens to MP3s through earbuds of which one is extracted. The consumer listens to streams from Youtube and Soundcloud laden with digital artifacts. The consumer likes to turn up the bass to full in their car, or perhaps the treble to full, not that it matters, the car system likely such anyway.

    So, testing the consumer is an exercise in futility and irrelevance. We can’t control how the consumer listens, and convenience is of far more concern than sound quality.

    Results based tests of summing certainly reveal a difference, but this isn’t about how a consumer reacts to it. It’s about process, and how the mixer or the producer reacts to the music. Summing makes mixing easier, but you MUST listen to the summing as you mix. This will affect your decision-making process throughout the mix. If you’re mixing off the internal -bus of your DAW, you will have to fight the maladies of digital summing (pinched width, low end, lack of punch, lack of depth, difficulty achieving relatively simple balances), whether you realize it or not.
    Our job as Producers is to deliver a track that causes people to react. If mixing is made easier, and therefore faster, your decisions are made fresh, and you are less likely to get bogged down on the minutiae of sound, and far more likely to concentrate your efforts towards the music itself, and the reaction you desire from the listener.

    If you want to test analog summing, it has to be a process driven test. All that matters is how that summing affects the producer. And forget about quick succession A/B tests in this regard. Those take the emotional impact out of the music. You have to hear the verse into the exploding chorus, for the chorus to appear to explode. So, mix for an hour using the 2-bus, then switch over to multi-outputs (create two session if you need to for speed of the switchover), and you’ll never, ever give a crap again what the consumer thinks, as it will make it so you can mix easier and faster. And if you can’t, then you just saved yourself some money. It’s not gonna prevent you from having a hit.

    Enjoy,

    Mixerman

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