An Interview With a Living Breathing Mastering Engineer


Lately I've seen lots of comments in audiophile discussion groups and websites about how bad mastering is the source of modern music's sonic ills. But how many audiophiles have actually met or talked with a mastering engineer? Not many I'll wager.


To help clear away the fogs of ignorance I see rolling across the Internet, Audiophile Review decided to ask a genuine working mastering engineer some questions.


David Glasser is the one of the founders and the chief engineers at Airshow Mastering in Boulder, Colorado (Airshow has another facility in Tokoma Park Maryland run by Airshow's co-founder, Charlie Pilzer.) Glasser has over thirty years of experience, and has mastered thousands of recordings, including more than 80 nominated for Grammys. He has earned two Grammy awards for mastering and restoration. The first was for the 1997 Anthology of American Folk Music and the second for the 2002 release, Screamin' and Hollerin' the Blues: The Worlds of Charlie Patton.



Glasser began his audio career with the Boston Symphony Orchestra, followed by eight years of recording and production for National Public Radio. After founding Airshow in 1983 to offer location recording services, he shifted to full-time mastering in 1990. Airshow Mastering expanded to a second facility in Boulder, Colorado, in 1997. Since then Airshow has grown into one of the largest mastering facilities in the country.



AR: What does a mastering engineer do? Why would someone use a mastering engineer?



DG: Simply put, a mastering engineer puts the final touches on a recording. That could include: dealing with levels - both song-to-song balance, and overall level of an album project; tonal adjustments - examples might include adding presence or high end to an otherwise good mix, or reducing muddiness and boominess. A lot of the job is working to present the mix in the best possible light, taking into account: the vision of the artist & producer, and other similar recordings. Also, mundane but important work including quality control, encoding for lossy formats, and metadata encoding.


Why do musicians use a mastering engineer? It's a fresh set of unbiased ears - hopefully working with the proper equipment in a well-designed room, and with experience to know what to do or not do.


AR: What forms do music files come in nowadays? Do you work with multi-channel or two-channel files? And what resolutions do you normally use?



DG: Things have actually gotten simpler as far as file formats go. PCM mixes come in as wav or aiff files, almost always 24 bit, and with sample rates from 44.1 to 96k (quite common) to 192k (occasionally).  Mixes can also come in as DSD files, which I import to a Sonoma workstation, or on analog tape.


We have well-maintained Ampex ATR and Studio 820 analog recorders with a variety of headstacks and replay electronics to choose from for tape-based projects. I always master at the highest available resolution and downsample as required for release. If there are multiple release formats - CD, LP, download - we encourage the client to cut the vinyl from our high-resolution files. Same for download - Apple now accepts high-resolution files for iTunes encoding. We also deal with legacy formats including PCM-F1, Genex, 1630, cassettes, DATs, and others, and we are equipped to make analog to digital transfers optimized for Plangent Processing.


AR: Walk us through what would be involved in a mastering session.



DG: It always begins with discussions with the artist, engineer, producer, and whoever else is involved in the creative process. We'll talk about what the project needs - sometimes this means very detailed instructions and suggestions. Other times I have carte blanche to do what I think is called for. I listen to the mixes - maybe not all the way through - but enough to get a sense of the musical direction. Then I try several approaches - different equalizers & compressors, analog and/or digital signal paths, etc. until I find something that works. I work on each song individually, in album order to maintain continuity.


Sometimes the initial settings serve as a template for the whole record, sometimes not. It's all program dependent. After this processing stage the songs are edited and assembled as needed, and the required masters are created. The client always receives a reference for approval before the masters are shipped. All masters go through a multi-step quality check process.


If it's a surround session, or a lock-to-picture project for DVD or BluRay, things get more complicated, as there are more options for surround, but the basic idea is the same: present the music in the best possible light.


AR: What was involved in the Grateful Dead Europe 72 box set project? How much time did you spend on it? Did you actually listen to every second of the recordings?



DG: Europe '72 was a dream project! I spent 7 months working on this - 3 to 4 days per week, occasionally more. I worked on each 3-4 CD show as soon as Jeffrey Norman completed the mixes and editing.


The Europe 72 tour was recorded on 2" 16-track tape. These multi-track tapes (2 pallets worth) were transferred by Jamie Howarth. The tracks were all put through the Plangent Process, which eliminates wow and flutter. I think this contributed to the clarity we were able to maintain. The Plangent-processed files were shipped to Jeffrey Norman who mixed the project. Jeffrey sent the 96k 24 Bit mixes to me, and after mastering, I sent references to him and producer David Lemieux for approval.


Occasionally revisions were requested. The masters were delivered electronically to Rhino Records via a secure DigiDelivery server. My workflow and mastering approach was established in consultation with Jeffrey and David during some initial test sessions, and variations on that basic signal flow were used for the entire 73-disc project. And yes, I did listen to every note. Several times!


AR: What is your take on the "Loudness Wars" issue? How do you handle clients who want to adjust/reduce the dynamic range for MP3s?



DG: "Loudness" is something that is usually discussed with the client for every project. Ultimately it's the client's project and his or her decision. My job is to give them the master they want, and if they insist on a heavily compressed master, so be it. However, things are looking brighter. Apple has just released their "Mastered For iTunes" guidelines, which contain 2 significant recommendations. The first is Apple's acceptance of high-resolution files (up to 192k 32 Bit) for submission to -the- iTunes.


Now Apple is not selling high-resolution audio (yet), but they acknowledge that their AAC encoder works best when fed by a high resolution source. The second important recommendation is to allow adequate headroom in iTunes masters. Lossy codecs can produce levels exceeding "0" resulting in audible distortion. Apple has released some software tools (Sonnox also has a similar software plug-in) that can help to optimize masters for better AAC encoding. Apple is also saying what we have all long known: highly compressed music sounds worse when converted to MP3 or AAC.


AR: What's your latest project? Why and how is it challenging?



DG: I don't have anything as massive as last year's Europe 72, but I'm working on a couple cool things. Look for a CD from the Bruce Kaphan Quartet this spring. Bruce is a pedal steel player (Sheryl Crow, Thomas Dolby, David Byrne) and this record is a very cool jazz-fusion project that's unlike anything I've heard. Also, I worked on the recently released Dave Carter/Tracy Grammar CD "Little Blue Egg," which contains unreleased songs and demos recorded before Dave's passing.


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