Tuesday, December 22, 2015

Acoustic Resources–New Gervais Tools

In his terrific book, Home Studio: Build It Like the Pros, Rod Gervais included links to a collection of very useful spreadsheet tools. I collected them into a single spreadsheet, labeled the tabs, and gave that to my MSCM students: New Gervais Tools. Rod provided us with calculators for Sabin RT60, panel absorber design, mass-law transmission loss, room modes, and quadratic diffusors.

Friday, December 18, 2015

Acoustics Resources–Sabin RT60 Calculator

When I taught “Acoustics” and, later, Room Acoustics at McNally Smith College of Music, many of my assignments directed my students to fool around with some spreadsheets I’d created to experiment with the effects of building materials and acoustics tactics. One of the most popular was an Excel file called “Sabin RT60 Calc.” I started work on this spreadsheet on the Office version that came about the time Office appeared on Windows for Workgroups v3.01, back in the late 80’s. It took a serious upgrade with Office XP and a bunch of additions in Office 2003, where its development stopped when Microsquash removed Visual Basic macros from Office.

The first tab in the spreadsheet is the “Sabin Calculator.” However, the coolest thing (IMO) about this spreadsheet is the “Materials List” tab, which contains data for 280 different acoustic materials from really slick RPG specialty absorbers to empty theater seats and wall board. The idea is that you can cut-and-paste the “Material” through the “8k” data into the “Sabin Calculator” room surface fields and build a pretty detailed estimate of your proposed room’s reverberant characteristics. I’ve used it in all sorts of room designs and, outside of room mode problems, it is very accurate.

If your room is relatively dead (<1.0S) or small (<3,000 cubic feet), the next tab, “”Norris-Ering Calculator,” uses the “Sabin Calculator” data to more accurately estimate the reverberation. The flaw in the Norris-Ering formula is that it can not cope with absorbtivities >1.0, which isn’t often a problem but can rear its ugly head with some exceptional specific frequency absorbers.

The “Measured RT60” tab is a place where you can put three sets of measured RT60 test data in a spreadsheet for averaging.

Finally, the “Helmholtz Absorbers” tab contains a spreadsheet with calculators for two different sorts of Helmholtz absorber designs, perforated panels and tube traps.

Best of all, it’s free and easily modified. If you add anything cool to the spreadsheet, I’d appreciate it if you would send me an updated version and I’ll put it on the site and if you “sign” your update it will remain on the spreadsheet.

Bullshit Audio Terms

I’m not even close to being the first guy to gag on the bullshit marketing terms applied to non-existent audio equipment qualities.

Immersive: As in “I felt the music was all around me. . .” (Other bullshit terms used for this generally non-existent quality are “open,” and “air.”) Bob Carver made a nasty audiophile device called the “Time Lens,” back in the 80’s. If you like “immersive,” you’d love this thing. This awful device screwed with mid and upper-mids L/R phase relationships so severely it was hard to locate any sound sources in some rooms. Carver had some really fancy explanations for why sound seemed to be originating everywhere but from the speakers, but simple test equipment (an oscilloscope) demonstrated the fact that frequency-dependent phase relationships were being messed with and the result was semi-entertaining until it gave you a headache. A surround sound mix can be “immersive,” if the speakers and listener are properly placed. Otherwise, stereo means “solid” which will always put the listener in a position facing the sound sources and, at best, a good mix and proper playback system will provide left, right, close and distant perspective. And that’s it. If you hear signals behind you, your system or room acoustics are screwed up.

Warm: (aka “creamy,” silkiness,” and “natural”) Ideally, you might hope this means some mild addition of even harmonics—mostly 2nd—distortion contribution that might seem pleasant. Usually, what most people call “warm” is the result of slew or crossover distortion and is in no way pleasant if you are used to listening to low distortion reasonably accurate sound reproduction. Distortion-wise, we tend to “like” what we’re used to hearing and if we spend enough time with low fidelity equipment and recordings we’ll learn to love that. That is not, however, a good thing.

Presence: Three decades ago, I had the pleasure of getting to mess with a Mark Levinson stereo power amplifier when I was a design and test engineer at QSC Audio Products. The Levinson claim to fame from advertising and reviewer hype was “presence.” hen I put a Mark Levinson amp on the bench, what I found was a slowly rising upper-midrange shelf that peaked at about 3dB at 3kHz (along with the associated phase distortion created by this built-in EQ). Otherwise, there was nothing special about this overpriced equipment in any regard. It wasn’t quick, it wasn’t particularly stable when super-sonic signals or reactive loads were introduced, and it wasn’t particularly low distortion (IMD or THD wise). A few moments with some simple electronic test tools would have dispelled the magical claims from a power amplifier with a silly built-in EQ, but audiophile magazines shy away from test equipment and objective listening tests.

Wide Dynamic Range: Dynamic range is a fairly straight-forward specification in audio equipment: “the ratio between the largest and smallest values of a changeable quantity.” At the most impractical theoretical extreme, the human ear is capable of detecting 140dB of aural signals. That assumes 0dBSPL as the threshold of hearing, which quickly deteriorates from infanthood to adolescence with age and noise exposure to more practical values of 15 to 30dBSPL. This also assumes the maximum sound pressure a human can tolerate and discern is 140dBSPL; a dubious claim at best. 140dBSPL is, for example, typically described as a full-throttle jet engine at 50 meters. A typical gun muzzle blast generates an impulse sound pressure level of 140dbSPL or more and that exposure is commonly known to cause permanent hearing damage. Relative to 1V (0dbV), the theoretical perfect (but practical) unity gain amplifier will produce 123dB of dynamic range. This can be bumped up to about 129dB if the relative maximum is 10VRMS. So, regardless of the unrealizable human hearing maximums, 123-128dB of dynamic range is pretty much as good as it gets in the real world. This relatively straight-forward specification and its associated practical limits are regularly ignored in the bullshit marketing world where numbers as insanely silly as “200dB” are quoted regularly and stupidly. Keeping in mind the analog thermal noise threshold, it’s useful to remember that every combination of amplifiers that produces an exponent of 2 (2, 4, 8, 16, 32, etc.) will reduce the combined dynamic range by 6dB. “Floating-point audio” or 64-bit or any other bullshit aside, physics and biology put an end to the realistic gains we’re going to get from playing with numbers.

This list of bullshit words is not by any means complete. I’ve left out color and taste sensory analogs, for example. A good rule to apply to modern ad-driven reviews and marketing claims is “any asshole can write marketing bullshit.” There is no one checking these claims with test equipment or even half-decent ears. So, if it sounds too good to be true, it is.

Saturday, December 5, 2015

Killing Music Loudly

I’ve owned a couple of recording studios, worked in a dozen studios owned by far richer people than me, designed a few studios, owned a sound company, designed and manufactured pro audio gear for six different companies (including my own, Wirebender Audio Systems). For 50-some years, amplification, microphones, and loudspeakers have been my life's major fascination and research subject. I taught recording studio design and acoustics, microphone theory and application, recording technology theory, and another half-dozen subjects at McNally Smith College of Music in St. Paul, MN.
 
With all of that behind me, I’m rarely encouraged by the sight of microphones and a sound system in a live performance venue. Almost all of my favorite live performances have been as close to sans-PA as possible. I used to play, and spectate, at a folk club in Dallas called “the Rubaiyat.” It was a 50-80 person club that served booze and bar food and hosted some of the best known folk acts of the 1960’s: Tom Rush, Tim Buckley, Pete Seeger, Peter, Paul, and Mary, Tom Paxton, Jim Croce, Arlo Guthrie, and lots of lesser-known talents including a spontaneous 2-15 member group we called “the Volunteer Jug Band.” There was no sound system of any sort in that club and the audience heard the performers just fine. I’ve seen a couple of shows at the Ted Mann Concert Hall in Minneapolis and those acts either didn’t use the house system at all or used it so carefully it was unnoticeable. In fact, that might be the key to running a great sound system.
 
The best known and most widely used live microphones in the world are a pair of coarse objects known as the Shure SM57 and SM58. The most critical quality these two blunt instruments bring to a stage is indestructability. The 58, for example, is known for its ability to be dropped from a 20’ stage to a concrete floor and not sound any worse than before the fall. Maybe the beginning to reinforcing sound rather than just making shit louder would be to get rid of the crappy tools and try doing the job well for a change?

Friday, December 4, 2015

On the Ground Video

More of a place marker than anything, but part off this video was recorded in our old Little Canada house.

Creating Space

One of the many things recording engineers (a grossly abused and debased title if there ever was one) talk about is “creating air” in recordings, especially vocal recordings and double-specially background vocals. Most recordists (a more accurate and humble word for what we do in recording studios) use EQ, delays, and misunderstood plug-ins to create “air.” Most recordists understand that there are a limited number of dimensions we have to work with in reproducing a musical performance: left-right (or all the way around in surround), louder-softer, and higher-lower frequency spectrum. There are, however, at least two other possibilities: front-back and lower-higher. Of course, phase distortion provides even more space-creating possibilities, but they are unpredictable and, often, weird. These additional dimensions are only available if the recordist knows something about acoustics and psycho-acoustics.

Acoustic_Guitar_Img_AIn a possibly hopeless attempt to convince a friend that her vocal group could benefit from a little microphone application knowledge, I went looking for some artwork to help with my descriptions. Luckily, Sterling Audio had exactly what I needed. The illustration at right is one of the points I was trying to make. My friend’s group is a fairly large women’s vocal group and their bandleader semi-wisely selected a collection of six low cost large-element condenser microphones with which he lines up in even spacing across the stage, randomly distributing the microphones across 11 performers. The original intent was something like the above illustration. Obviously, 11 into 6 produces a significantly different dynamic, but the flawed concept is the same.

Performance-wise, the problem is even more dramatic. During a recent show, I solo’d up each vocal mic and discovered that the vocalists could be counted on one of two possibilities: 1) some singers naturally gravitated to grouping around a mic and singing “together” and 2) some naturally filtered to an abandoned mic and sang “solo.” If you’ve never sang in a group this might surprise you, but if you have this will be a no-brainer: the solo vocalists were consistently off-time and key and the together vocalists consistently delivered stronger, tighter, more in-key performances. So much so that I found myself naturally fading-out the solo mics and blending the group performers by ear, as I pulled down disagreeable faders and pulled up the performances that blended well.

Acoustic_Guitar_Img_A
Most recordists think the best way to record any signal sources more complicated than one voice is to distribute as many mics across the various sources as possible. Hell, hip-hoppers put two mics on one voice to optimize phase distortion and tonal weirdness. Here’s where I disagree with “common knowledge,” regarding the best way to record/reproduce/reinforce a group vocal. Sterling Audio’s article suggests, “There may not always be enough resources for separate microphones or recording tracks” as a reason for simplifying the number of microphones involved. I think the recordist better have a damn good reason for using more than a stereo pair in this kind of situation. “Depth of field” comes from the various time delays caused by the distance of the sound source from the mic. Vocal groups, horn players, and ensembles are often perfectly capable of figuring out where they should be, physically and sonically, in the mix and allowing them to perform for the microphone as a listener often produces incredible results.

beatles recThe fascination modern recordists have for vintage recordings, oddly, doesn’t seem to extend to vintage recording techniques. Due to the lack of console and record media channels, the old-school guys were forced to learn something about microphone polar patterns, acoustics, and music. Today, “more is better” and too many recordings have the spacial characteristics of a pair of headphones.
3296486-beatles
Beach-Boys-Bruce-Johnston-Carl-Wilson-Al-Jardine-Dennis-Wilson-Mike-Love-Pet-Sounds-session-19661c93ef2c484b038aa03e60bc261bdb13fThe Righteous Brothers. Courtesy Polydor.

POSTSCRIPT: A friend and ex-student, Steven Sullivan, took all of this to heart and produced a record limiting himself to no more than 8-tracks and very few effects. 

A Beginner's Guide to Self Immolation

is the record and it well-deserves your attention. Steven says the idea behind this record was, "The original idea for this album was to go back to basics and record things very simply. I had grown tired of modern recording and mixing techniques and decided to put some self-imposed limitations on the entire tracking and mixing of the album. It changed a little as the process went on, but basically I only used one mic, a long ribbon mic, through a 1950s design preamp and opto compressor, and that was it. So I'd go in the tracking room, point the mic at the piano, play through the tune, scoot the mic closer to the drums and play the drums, go sit down with the acoustic guitar and move the mic closer to it, stand up and sing, and it really allowed me to focus on the music instead of the technology. Part of my concept was that it would end up sounding kind of home made and low-fi since I'd limited myself so much, but to my total surprise it ended up being maybe the highest fidelity, most organic, best feeling record I've ever done."

Wirebender Audio Rants

Over the dozen years I taught audio engineering at Musictech College and McNally Smith College of Music, I accumulated a lot of material that might be useful to all sorts of budding audio techs and musicians. This site will include comments and questions about professional audio standards, practices, and equipment. I will add occasional product reviews with as many objective and irrational opinions as possible.