Last show of the season with TBT. Having already done this show in Dallas @ Dallas City Performance Hall, I have a solid grasp on what is necessary for each piece. I’ve actually upgraded by Qlab playback rig in order to have more discrete outputs to feed the PA. Where in the past I’ve fed the sound system with L/R and monitors, I’m now sending a SUB L/R feed as well and may even go the extra measure to feed the center cluster discretely. Why? It give more options for sending things at different levels directly from Qlab. For example, one of the pieces in First Looks requires no low end for some of the music that plays at intermission (think elevator music) while the main music requires lots of low end. One could manipulate the audio prior to playback so that this is accomplished at the audio file level which I may still do but I certainly don’t need to feed any music to the subs that don’t want low end. Here is what my Qlab outputs look like:
1 – Main L
2 – Main R
3 – Monitor 1
4 – Monitor 2
5 – Sub L
6 – Sub R
7 – Center cluster
8 – pilot tone (used to for redundant auto switching)
Tomorrow we will tune the stage monitors and then I’ll post some Smaart traces
I found this article doing some research about the L’Acoustics VDosc technology. It’s certainlt worth reading if you aren’t already familiar with the history and concepts of line source versus point source.
gtaust.com – part 1
gtaust.com – part 2
gtaust.com – part 3
“When Show THD is enabled and the RTA graph is set to a fractional-octave resolution of 1/12th-octave or higher, the notation THD: n%, will appear in the cursor tracking readout above the RTA graph, where n is the THD percentage value calculated for the current cursor frequency. THD values in Smaart are the ratio of the power in the fractional octave band at the cursor frequency, to the sum of the power in the next three harmonic frequencies. If (and only if) the cursor is positioned at the frequency of a single sine wave being used to stimulate the system under test, this value should be indicative of the total harmonic distortion present in the system at that frequency. Otherwise, it is generally meaningless” user manual pg. 84
Bennett Prescott – Two Processors PDF
bennett Prescott – DSP Differeneces PDF
Here is a youtube video made by Fulcrum Acoustics showing the same basic concept of DSP’s being vastly different in function when set the same:
Fulcrum Acoustics – Youtube DSP
I have been contemplating purchasing a Roland Octa-Capture audio interface for measurement purposes and Qlab playback purposes for the last 6 months or so. After having some long discussions via text with Arthur Skudra about the device and it’s value as a audio measurement device and also getting official verification that the device can provide enough P48 phantom power for up to (8) Earthworks mics at 10mA each, I decided to place an order. I now have (3) of them.
Before I continue I must point out something rather alarming about the device. It comes with a pair of 1RU rack ears but the device itself is taller and you can’t rack mount one without leaving a space between it and the next device. This is a big bummer and I may return two of the three and get something else for playback purposes and hold on to one Octa Capture that I leave the ears off for portable measurement purposes. Stay tuned.
If you’re not discouraged by a device that isn’t rack friendly but very portable, read on. The Roland Octa-Capture is a 8×8 analog audio device with a headphone output with separate volume control, MIDI I/O and SPDIF I/O. With a street price of $500 USD, it’s an interesting device to consider for measurement purposes.
Today I sat down with the device to see what needs to be done to configure it to work with Smaart V8. A few pointers. There is a default setting that appears to be only accessible from the front panel of the device that allows you to turn off a power saving mode. Setting can be either OFF or 4 hours which is the default. Not sure I like that default but all of my boxes will be set to OFF permanently. Next you want to mute all the inputs so that you don’t cause a feedback loop. You never want to send your measurement mic signals to the main outputs!!!
After posting about the unit on the Facebook Rational Acoustics Smaart group, I was handed this helpful piece of information regarding inputs 7 & 8.
Rational Acoustics forum – Roland OctaCapture input levels thread
Rational Acoustics forum – Roland OctaCapture Listening Test
Yesterday as I was putting the Fort Worth Opera festival back into the warehouses, I spent a moment looking backward and realized that I’ve probably tuned 100+ sound systems at this point using either SpectraFoo Complete or Smaart 7 or 8. I can’t speak for others but what is clear to me is that without a measurement rig, you’re severely handicapped. Some people draw the line between system tech and sound engineer. For me, those are two sides of the same coin. Who better to know when the system is ready that the person who will be using it or IS using it right now? Dave Lawler has explained that on past performances he has tweaked the system during the opening act and then continued to fine tune things during the actual headliner performance. What this means is that there is no line. There is no point at which it’s time to stop paying attention to the performance and “tune” out. If the person mixing is also the system engineer, there will be a natural curve from beginning to end where things get better and better. I will admit that the first 10+ times I attempted to tune an actual system, I was somewhat clueless as to how to tackle it. I’ve made lots of really silly mistakes along the way but each tuning has been a refinement of understanding the basic concepts necessary (thank you 606!), and the building of a solid foundation where theory becomes ingrained knowledge. Where text book examples are discovered in the wild.
There is a certain amount of hours I think need to be spent in the shop / living room / garage / etc… before you head out with your rig to measure and tune someone’s system. It’s like taking someones car for a drive. You need to know your way around before you should turn the key. In my case I’ve had the opportunity to watch well trained engineers do their work and be able to ask “ignorant” questions along the way without fear of ridicule.
I recently purchased a used MBNM 550 EL measurement microphone on eBay for $99.95. The mic arrived and I plugged it in yesterday to compare with my other measurement mics. Zero output. Dead On Arrival.
Many times with eBay sellers, it’s like pulling teeth to deal with a situation like this but I was pleasantly surprised to receive this response back from the seller:
“Sorry about that, please keep the item and recycle it or use for parts, I’m sending you a refund now”
I immediately got an eBay message stating I’d been credited the full amount.
To Whom It May Concern, the following Earthworks M30 matched pair is for sale. Seller is asking $2000.
Contact the seller directly if you’re interested:
Here are the specs for the microphones:
Frequency Response: 3Hz to 50kHz ±1/-3dBPolar Pattern: Omnidirectional
Sensitivity: 36mV/Pa (-29dBV/Pa)
Power Requirements: 48V Phantom, 10mA
Max Acoustic Input: 140dB SPL
Output: XLR (pin 2+)
Output Impedance: 65Ω balanced (between pins 2 & 3)
Min Output Load: 600Ω between pins 2 & 3
Noise: 20dB SPL equivalent (A weighted)
Dimensions L x D: 229mm x 22mm (9 x .860 inches)
Weight: .5 lb. (225g)
Looking forward to visiting the DCPH tomorrow and seeing house A1, Jason Wagner again. Jason took Harry Brill Jr’s Smaart 7 class last year in Fort Worth and has hopefully made some progress optimizing the house sound system. A lot was learned last year when Texas Ballet Theater was in the building. Maybe this time around we can make further improvements for the benefit of all.
Part of using a system correctly is data gathering. Each time I visit this venue I’m better equipped to measure and understand how the system works, what the system consists of and how to optimally use it.\
Here are a few details from the system designer and loudspeaker provider:
Jaffe Holden – Dallas City Performance Hall PDF
Fulcrum Acoustics – Dallas City Performance Hall PDF
QSC’s QSYS is an industry standard DSP platform.
Before you try to use a QSYS system, it may be beneficial to watch the online training videos.
LEVEL ONE Online
Q-SYS Quickstart Tutorials
The two main venue’s where my clients produce shows are Bass Performance Hall in Fort Worth Texas and Winspear Opera House in Dallas Texas. Both venue’s have BSS London BLU DSP systems and so I have been building my own BSS London BLU rig so that:
A. I know how it works and what is possible with the system
B. I have a system that can cover my own DSP needs
C. I am learning a DSP platform that is fairly standard in the audio industry
BSS London BLU is not inexpensive but by being patient and purchasing used on eBay, I’ve been able to assemble a fairly capable and affordable DSP rig.
Unlike some stand alone DSP devices with a fixed architecture, BSS London BLU is a DIY platform. Once you’ve chosen the desired hardware (including how many inputs / outputs / GPIO / etc…) you start with a blank virtual canvas and via device blocks, build whatever you need. What this means is that there is a learning curve just to get audio to pass through the box but at the same time you can achieve things not possible with a fixed architecture device.
Fortunately companies that produce open architecture DSP systems know that there is a learning curve and typically provide an online training program. In the case of BSS London BLU, the video training series can be found here:
bssaudio.om – videos
With any open architecture DSP system, seeing examples of how to achieve the desired result is helpful to learn how to use the interface.