Bob Katz Interviewed
As an engineer, audiophile, developer and educator, Bob Katz’ contribution to the audio world we know today can not be underestimated. MTM finds out more...
Soon after Bob had joined other professionals for talks about the Loudness War and its future at the TC Electronic Rome Calling event, we caught up with him for a chat back at his base in Florida to find out more about his efforts to standardise levels in music. But to understand Bob’s concern for quality, let’s first look at his journey from the beginning, which has culminated in him becoming the well-known author and mastering engineer he is today.
Bob’s forays into music started with him playing the clarinet while also exploring the technical process of dismantling and re-assembling tape decks. As his passion for high-quality audio grew he became an invited attendee at local audio stores, offering his opinion at audio kit demos. During his years at college he took an interest in the faculty’s radio station, becoming recording director and presenting his own DJ show. Given his interest in analogue and digital electronics, he tells us about the time that led to him becoming a mastering engineer.
“I was the audio supervisor for Connecticut public television and on the side I had built a recording system. Weekends, evenings and vacations would be spent recording bands, groups and orchestras. So I was always a music recording engineer. Then I decided to leave my supervising job when I got the opportunity to work at a 24-track studio in Vermont. After working there I moved to New York and worked at a commercial studio while still recording music in my spare time. Eventually I became fully freelance and worked on my own. Then David Chesky picked up an article written about me in the Village Voice. I was just what he was after at the time – an engineer who was also an audiophile. I became technical director for Chesky Records and we released a number of tracks that are often referred to as historic audiophile recordings. I opened my mastering studio around this time as well.”
As well as being a mastering engineer, Bob is well-known in education circles for his book Mastering Audio:The Art And The Science. It’s currently in its second edition and is an excellent resource for understanding the fundamentals of analogue and digital audio, along with many elements of mastering that are considered a ‘black art’. He is currently working on the third edition (due out later next year), which he tells us will contain information on some radical changes in the industry and his predictions on where mastering will be by 2020 and beyond. But before we jump too far ahead, we asked Bob about his concerns today for the audio industry and how we got ourselves into this situation in the first place…
Peak abuse
As part of Bob’s mission to try to maintain audio quality within the mastering industry he introduced the K-System to give the user more focus on average levels while also providing peak levels as well. Bob explains the current problems with metering: “In the second edition of my book I made it clear that the K-System is an intermediate system, a bridge between peak metering and getting people on the right track. In the digital age, many people have a normal peak meter in front of them and it can be very deceiving. It makes them think they need to get their levels up to the top of the meter. Peak meters encourage loudness-envy, and working your level high doesn’t actually directly affect loudness. Around 2004 I realised that peak meters and peak normalisation are the root causes of the extreme loudness race, which causes severe distortion, loss of clarity and dynamics. Engineers keep on pushing the average level with a fixed peak level until there is no peak-to-average difference at all.”
For a long time, all programme material has been normalised to full-scale peak, which means that there is no loudness standard: “Everyone pushes their loudness without realising how much that damages their material in a system with a fixed maximum peak level. Over the years this has meant a reduction in the crest factor, which is a ratio of average level (RMS) and peak level.”
Bob tells us about his ideas for the future of metering: “I wrote to my friend Thomas Lund, who is a very brilliant engineer and researcher for TC Electronic. He agreed with my views as he was thinking along the same lines, so the two of us continued to think about this peak problem. I’ve realised that we have to get rid of the peak metering portion of all loudness meters because they still end up trying to get their peaks to full-scale. What we really need to end up using is a meter with just a single peak warning light, and this should be a true peak indicator which will include intersample peaks. This would work alongside a loudness meter. If this loudness level is low enough when compared to the peak level it will allow plenty of headroom, room for clarity and dynamics when people want it. The people who want their sound to have more compression will just end up with more room between their peak level and full-scale. The logical stage is to standardise this level of loudness for everybody – that’s the hard part, but it’s where things have to go.”
Bob tells us that as things are today, he has to make the same sacrifices most engineers do to make material loud for the client: “My masters are far more compromised today than they were five to ten years ago. Any mastering engineer who says different is either living on a desert island, has plenty of audiophile clients or is lying. But regardless of this situation, a lot of the techniques we use to make something appear louder is just that – to appear louder, not necessarily better. Extreme limiting, compression and clipping are all used for this task and I think the problems will become evident when we have loudness regulated and all tracks are played at the same perceived volume. It will be hard to convince people that extreme styles of production sound good when the downfalls of these techniques are easy to hear objectively when playing alongside more open, natural-sounding tracks at equal playback loudness.”
Going to War
The Loudness War is the main aspect of what Bob sees as the primary problem within the industry today. But we wanted him to tell us exactly what he thinks we are losing when things are processed to achieve that Holy Grail of loudness. He explains: “The first thing to go is stereo depth and dimension. More compression just closes in the width of the signal. There’s something about compression that emphasises the mono component of the signal.
“The second thing we lose is excitement. Last week I mastered a country album that was more American country than pop country, so it’s supposedly not as pushed as pop country. I mastered a single first for the producer and we were both happy with it. Then, as I mastered the album, I had a bit more time and I discovered that if I dropped the level travelling into the peak limiter by 1dB, instead of sounding softer it sounded louder. This is because it had reached the point that pushing it into the peak limiter any further was pushing things down too much and this squashing effect was causing a loss in definition. I mention this to enforce the point that there is a point of potential loudness in any track that can’t be exceeded.”
Asked about kit, Bob revealed some interesting views about his favourite peak limiter: “Very few programmes need digital peak limiting (as opposed to analogue peak limiters, which by comparison are usually quite gentle). There is no digital, sample-reacting peak limiter that’s very good, just a few that don’t sound terrible. I use the PSP Xenon or the peak limiter in the TC 6000 system. They both have good auto-release curves and don’t add too much distortion. This makes them pretty invisible. But on average I won’t apply more than around 1dB of peak limiting. Too much digital peak limiting of this type tends to punch holes in the sound. Peak limiters are, however, a necessity given the demands of the loudness race.”
Peak to distortion
While we talked about the confusion between peak metering and the use of peak limiting, Bob offered some interesting information on how the added distortion from extreme processing gets worse down the media chain. On compressed audio formats: “They are far more sensitive to the kinds of distortion caused by extreme loudness. Distortion can accumulate really badly when a file is converted, especially to lower-quality files like a 96kbit/s mp3. Some people will say, ‘we don’t use 96kbit/s any more, we use 320 etc’ and it is, of course, less of an issue at higher bit-rates, but we must remember that satellite radio can use bit-rate reduction as low as 28/32. Clipped masters can sound really gritty and distorted when converted to a compressed format. I’ve done demonstrations of this in my talks, when you take the compressed file and reverse its phase alongside the original WAV to leave you hearing just the difference created from the file conversion. Just listen to some cheap, dirty mp3s through the side channel only and you’ll be persuaded to avoid these problems. You’ll hear all of the added distortion, terrible high-frequency aliasing, noise, space monkeys, squirleys and much more. The more natural and unclipped the uncompressed recording is, the fewer side effects you’ll get after conversion. Monitoring the side signal when converting is a good way to check for these artifacts.”
Into the future
There is a new standard from the ITU setting out a general agreement to match audio levels in broadcast by loudness, not peak level. This was started by research and collaboration among the European broadcasting entities under the auspices of the EBU. This also has the potential for consistent music levels in the home. Bob tells us about its success so far: “In the Netherlands, Denmark and a few other countries in Europe the radio stations are already broadcasting with the new ITU loudness standard and sounding better. The next step is for iTunes to use loudness monitoring by default so tracks are matched to the same perceived loudness. When this happens I think things will change rapidly. We’ll no longer be pressured to push our masters as they won’t need to be as loud as the competition. It will be a real game-changer.”
This feature first appeared in Music Tech Magazine issue 103
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