At the beginning, Christoph Stickel talks about the history and the different aspects of mastering:
Dirk Sommer: Christoph, just tell us what mastering is all about.
Christoph Stickel: It's always difficult to describe the demarcation between recording and mixing. Let's look back a few decades, to the 1960s. In the production chain, after recording and mixing, we have the transfer from the master tape to the lacquer for the vinyl release. Now somehow the information has to be transferred from the tape to the cutting stylus. The tape machine, for example, is quite unproblematic in terms of phase, also in terms of the proportion of high frequencies, dynamics and much more. The vinyl, however, is not. Technically, you have to take care of what is on the tape to be later cut onto the record. During this transfer, adjustments often have to be made. That can certainly change the sound and the volume. And then it turned out in the mid-60s that there were a few records that were louder, had more bass, less noise and simply sounded better than the others. Because the engineer who made the transfer didn't just look at the measurement values in between, but also pricked up his ears and thought about the sound, making it both technically and sonically perfect.

That was basically the point of origin of creative mastering, that you try to process the great recording you have at hand in such a manner that it then later sounds in an optimal and maximally musical way for the targeted medium. There is a very nice metaphor by Steve Hoffmann that aptly describes mastering. He appropriately says: You have a work of art, for example a painting, that you want to present in the best possible form. You now take it to a gallery, with white lights, bright sterile walls, to draw the focus solely to the picture. On the other hand, you can use strobe lights or create a lightshow to stage this work of art perfectly, so that what exactly makes up the respective work of art comes into its own and shines even more. Now you still have to photograph this state of condition, this presentation, in order to then reproduce the photo. That means to process the music sonically in such a way that it ends up sounding perfect. Just like trying to find the best-sounding stereo system for your music. You know that very well yourself. You have certain tracks that sound fantastic on one speaker and rather pinkish on others. In mastering, you try to build the perfect loudspeakers for the respective recording, metaphorically speaking. Of course, there are also technical aspects: The mastering engineer is the person who listens to a record for the last time before it is duplicated. He is not only responsible for making it sound wonderful, but also for ensuring that it is technically flawless: Is there perhaps still a crackling noise, has there been a distortion somewhere, is there a mute? That's what really stresses me out personally as a mastering engineer, but still it's a very important part, which is why I've also become a bit paranoid about it. There might be something left after all! Is everything really OK? The producer or musician then listen to the master again, resuming in the best case: "It sounds wonderful, Christoph. That's exactly how I want it." But in the end, I am the one to listen to the master for the very last time, and if there's a mistake left and I didn't notice it, I am the one who eventually has to take responsibility for it. So it’s on me to make sure that the sonic and the technical aspects are faultless. There’s something I always like to tell my students: You can take out a professional liability insurance as a sound engineer, which you should. It's not that expensive for a normal recording engineer. But if you tick the box "I master", it costs several times as much. The consequences that can arise from mistakes can have a greater and more unpleasant impact: recalling a complete CD pressing back from the shops, having it pressed again, shipping it out again, and etcetera.

That means that mastering combines everything from art to technique. In addition, there are also details that I consider quite important and not at all uncreative: for example, designing the transitions between individual tracks correctly. I.e. I have two titles in a row. How long should the pause between them be? By default, it's two seconds on iTunes. That can fit, but often it doesn't. Does there need to be some silence here to let the previous piece have more of an effect, or does the next track have to follow with some "attack" to propel the album? These are such really filigree, seemingly unimportant details, but which then make a work into a whole. It's also important when we have several tracks on a record, on a CD, or a playlist, that the volume of the individual pieces should be set in such a way that the listener doesn't have to reach for the volume control to readjust, in order to let everything fit together well. Also an important role plays as soon as we leave the field of classical music - and even there I am increasingly encountering it - that we must not fall off in direct comparison even against the competition. For example, I now have the Sebastian Müller Band here, which we will listen to later. If you leave the mix with its original dynamics, the end product would seem small, thin and dull in direct comparison to other releases in this genre. It must not stand back significantly in a playlist, for example, or it will be skipped immediately. At this point "Dynamic restriction" is required, a term which will probably conjure spots on your face as a high-end afficionado: But this can also be performed very tastefully up to a certain point and give the power, the punch of the music, yet another new dimension. On the other hand, of course, it can kill the music. A very difficult subject. Just think of the loudness war.

These are roughly the things that happen in mastering. Besides that, of course, what are the formats that are currently being consumed? Professionally, I started when the CD was just about to overtake the vinyl record. I got learned to the CD, then MC, then DCC, Minidisc, SACD, DVD and all the other formats that came along. Now we are at the point where we are increasingly moving away from physical media - apart from vinyl, of course. Now we have to supply material to a wide variety of online portals. There are various specifications that change again and again. That means that each portal may do things a little differently and have its own special features. The risk lies not only in the circumstance that the product could fall through a technical grid, but also that it doesn't function properly there and can't really live up to its full potential. Then, of course, we have the high-end formats in the highest resolution, which we also all have to serve reasonably. In addition, the world is increasingly becoming immersive. That means even more formats coming along.

Next to the ears, the most important tool for the mastering engineer are his sound transducers:
CS: Here with me, you see an awful lot of buttons and knobs that are a lot of fun. And actually, they're the ones that everyone looks at first. But the most important thing about the whole procedure is that I hopefully have reasonably clean ears and that I am able to really evaluate what I'm hearing. We have calculated and calibrated the acoustics here. I have an acoustic space here that has got a defined reverberation time, defined reflections, balanced modes and everything I need to hear and judge optimally. Then I’ve also a loudspeaker system at hand with which I can perceive what I hear linearly, as musically correct and clean as is possible. So listening is the be-all and end-all of mastering. The prerequisite is that I have a listening situation in which I can evaluate objectively. Only when I really hear what I am doing, I am able to intervene sensibly, modify it, improve it, sometimes even repair it. Only when I hear properly do the many, beautiful buttons here make any sense at all.
DS: What kind of speakers are you using at the moment?
CS: I have worked with the Kii Three for several years and have been very satisfied. A few months ago, monitor db supplied Jürgen Becker’s big Convergence to me. The Kiis are now used more as nearfield monitors, while Jürgen Becker’s Convergence got to be the main speakers now, and with which I am perfectly happy. That's what is around in terms of loudspeakers. I have also recently started using the Dan Clark Audio headphones. In my 30 years of work experience, I have always been someone who liked to work with headphones as well. I started with the K1000 from AKG, this thing you clamped on your head, I thought it was great. Then Stax and Audeze came along, followed by the Dan Clark model, with which I came into contact during the last High End show in Munich for the first time, and which I am very enthusiastic about, using it now also for work. You could ask, why do you work with headphones at all? There’s this very expensive acoustically optimized room. There are loudspeakers that account for tens of thousands euros. So, why did you now come up with the idea of putting on headphones? I can only speak subjectively for myself as to why I like to add headphones. It's a different listening situation than in the room, here I have the signal very close to me, it's directly at my ears. When I perform the most delicate adjustments, for example the pre-delay setting in the reverb: whether it really has to set-in five milliseconds earlier or later, I can hear it very clearly through the headphones and thus make the perfect adjustment. When I set up a compressor, what will the attack and release times be like? Do I get that certain punch or do I spoil it up? The extraordinary proximity I have with the headphones allows me to get that delicately adjusted. Of course, all of that to finally be heard and adjusted through the loudspeakers. That's a real interplay. The other benefit I get from it is the "technical listening". By this I mean, as I already mentioned before, detecting technical faults such as pops, hiss, distortion and sizzle. These are problems that one might miss faster when listening through loudspeakers. I almost always listen through the last version with headphones. Also because, as stupid as it sounds, I am sitting here, moving around, my arm on the desk probably making a noise or the chair creaking. It simply distracts me. Was there something, or not? With headphones, of course, I do no longer hear such things. And no matter how I move, I always stay in the stereo centre. That's this kind of extremely focused listening, separated from the environment. But ultimately, my sonic decisions are always made on the loudspeakers. However, one particular thought does cross my mind: How is listening done out there? Probably more and more by using headphones. In my observation, it’s actually the medium that is used a lot by the masses. On the train, underground or bus, I mostly see people listening through any kind of in-ears. I can no longer state that this is still the secondary form of auditive consumption compared to the loudspeaker. As to my experience, listening through headphones - of whatever quality level - increasingly makes up the majority. The good old stereo that we grew up with is no longer widely used by the masses; instead, people are more likely to spend money on headphones.

In this context, mastering with headphones is becoming increasingly important:
DS: Christoph, don't you perform mastering differently when using headphones?
CS: Yes and no. I would like to use an analogy here. At some point I was asked by a student, I think almost ten years ago now, "Christoph, do you also listen through an iPhone?" I refused to accept it and replied I would never do that, and if it ever came to that, I would look out for a new profession.
DS: With good reason.
CS: I am also noticing that with my children, who are around 20 years old, that their music either plays through headphones or the mobile phone’s in-built speaker. Of course, I've also bought them speakers and other gear. But I guess that's the new reality. I never monitor through these little speakers, but I do have them on my radar. As to my experience, if I'm working in a very good monitoring situation, then it fits all the other speakers as well. Of course, while one speaker is a bit boomy, the other sounds a bit thinner, depending on the basic sound characteristics of the speaker. But there will always be a happy middle way once I have created a clean sonic image. This also applies to playback on mobile phone speakers.
But let’s go back to your question: Do I have to change my way of working and rather optimize the sound for headphone playback? What is the main difference between playback via loudspeakers and headphones? Of course, with headphones we almost always have an in-head localisation. There is a pronounced left/right detection. This means that our stereo image is different from what we know from loudspeakers in the room. But when I try to optimize a normal stereo production for headphones, to create a soundstage with all my might, it mostly backfires. With a lot of luck, it will be a touch better for the headphones I am using at the moment. But this is not compatible with others.
Again, the mastering I did on speakers sounds similar on most systems and is also compatible. However, I notice that I have to work very cleanly in the low frequency range, as the headphones don't forgive me anything. Especially with very good headphones, bass reproduction is something different than with many speakers. I have to put a lot of effort into hearing the bass cleanly through the speakers: The listening room must be in excellent shape, too. The speakers have to be really good ones and the room's modes have to be equalized in order to reproduce and perceive really low frequencies in a clean and controlled way. Headphones can often do that better. With very good headphones, I am able to hear the lows better than I do in a normal loudspeaker listening situation. This means that the consumer will notice my sloppy work in this frequency range more quickly with headphones.
DS: I think a lot of headphones are so intense in their bass reproduction that if you were to mix with them, you wouldn't have any fun listening to the result over a stereo.
CS: Exactly. Then I would have lost the game. But as I said before, if I listen here under optimal conditions and get the bass range spectrally balanced, it will also fit in most other listening situations. A headphone with a bass boost will reproduce more bass if I have worked cleanly, but without resonances and without booming.
In my work, the loudspeaker is my utmost reference. Here, everything has to fit. With the headphones, I work on filigree details to then finalize them on the loudspeakers. When I'm satisfied with the mastering and have heard everything through the speakers, I usually give it a final pass with headphones. As I said, I use them to concludingly listen to potential technical errors in a dedicated way, to then probably notice that my fingers went up for some journey over the equalizer panel having made small readjustments along the way. So we end up talking about the quarter of a decibel here that perhaps I only imagine I still hear. But I did make the small adjustment, double-checked it then on the loudspeakers and found that it was well done.

For the author, headphones and spatial imaging are practically contradictory. The professional, on the other hand, takes a much more differentiated view:
DS: Spatiality is always very important to you. When we tried out the Audioquest Niagara units, you noticed that there was even more spatiality in your edited pieces than you had heard before.
CS: Yes, absolutely.
DS: Can you also verify and perhaps even create a spatial impression with headphones?
CS: Well, what I can do very well with headphones is to set the reverberation. What I'm personally still struggling with, but slowly getting there, is to really define spatial impressions, that is, a depth gradation with the headphones. Not just being able to say the instrument is located in front of another, but clearly hearing its position on stage. That's where I'm at, but I had to learn that first. The stage isn’t deep, but more spread out left and right, and more dedicated. I enjoy listening to that, to perceive the tonal colours and also those spatial impressions.
DS: I have never experienced the impression of depth, no matter how good the headphones were.
CS: I guess you have to distance yourself from the loudspeakers and get involved with the headphones. Then you can feel it. Not the portrayal of size, but the depth gradation is definitely there. It's probably a matter of practice.