Notes from the Test Bench
By Bruce Hofer, Chairman & Co-Founder, Audio Precision
Hello and welcome to the August edition of Audio.TST.
This month we look at some user questions about graphs in AP control software and follow up on last month’s article about pre-analyzer filters with an FAQ.
For those of you outside the USA, I’ll be speaking in Korea and Amsterdam in September (see Events below). I hope to see some of you during my travels.
Bruce
Output: Tech tips and new applications from AP Working With Graphs in 2700 Control Software
A user recently wrote in asking how to take 30 separate tests and display them in one graph in ATS and 2700 Software. This is often done to compare various results more easily, but it can trigger some formatting issues if you’re not careful.
Appending data
The first step is to append all the data into one graph.
- Open the first test file containing one set of data (trace).
- Select File > Append and locate the saved data you wish to add to the graph.
- Repeat step #2 as necessary until all the measurements you wish to display are on the graph.
Scale and Formatting
All graphs have to have a scale. If the values of appended data are greater than the scale of the first test file, then the data will not be displayed as it is “above” the top limit of the scale.
The Optimize feature in AP software will automatically resize the graph so all the values are displayed. Just right click on the graph with your mouse and select “Optimize”.
Sometimes a problem can arise if the scale is too large: it becomes hard to see individual lines. Changing the formatting of the lines can make them easier to see, for example making them thicker, adjusting the colors or varying the style for greater contrast between measurements.
Go to the Legend of the graph and alter the line formatting one measurement at a time. You will see the results live on the graph. If you want to print the graph with the altered formatting then go to File > Page Setup and select the Trace tab. Tick “Track display changes”. All the formatting visible on the screen will now be sent to the printer as well.
For more on manipulating graphs in AP control software, read the June 2006 issue of Audio.TST at the AP Audio.TST Archive. As always, AP Tech Support is available at ap.com/contacts 5 days a week to help with any instrument questions you have.
Sound Advice: Audio Test Q&A
Last month we looked at the need for pre-analyzer filters. Below, Bruce Hofer and Tom Kite follow up on some of the subtle differences between the AUX-0025 and S-AES17 filters.
Q. I need to measure a class D amplifier. Which filter should I use?
A. It depends on whether the output filter built in to the amplifier is adequate. If it is not, or if there is no filter at all, you need an AUX-0025 to remove switching transients before they reach the analyzer.
Q. I have a conventional linear amplifier. Do I need a filter?
A. No, the measurement filters present in the analyzer are sufficient.
Q. Is the AUX-0025 a substitute for the S-AES17 filter?
A. No, the two are used for different reasons.
The AUX-0025 filter is external and passive, and must be driven by a low impedance source such as a power amplifier. It prevents large switching transients from reaching the first stage of the analyzer and causing measurement errors.
The S-AES17 filter is internal and active. It rejects out-of-band noise so that the analyzer autoranging circuits function correctly, and so that measurements are tightly band-limited.
Q. Why do I need the S-AES17 filter?
A. There are two major reasons you may need the S-AES17 filter.
First, a device such as a DAC may have a lot of out-of-band noise in its output. The analyzer input range needed to accommodate this noise may be too high to accurately measure the signal. The AES-17 filter removes much of the noise before the autoranging circuits.
Second, you may want to make measurements to the AES17 standard. The specifications of the S-AES17 filter exceed this standard.
Q. Why can't I use the built-in 22 kHz lowpass filter when measuring DACs?
A. Typically the rise of out-of-band noise in high-order noise-shaping DACs is faster than the roll-off rate of the 22 kHz lowpass filter. The noise is therefore not attenuated enough to make accurate measurements. The AES-17 filter has a much steeper roll-off. Also, the 22 kHz filter is located late in the analyzer signal path and cannot protect the input stages or autoranging circuits from out-of-band signals.
Test Results: AP News & Events
AP News
Improvements at AP.com
We’ve made some changes to the AP.com website to make it a more useful resource. The big difference you’ll notice next time you login is we now require a password for every account.
Creating a new password is painless. When you hit the login page on AP.com, just enter the email address you used to register with AP when you first signed up (the same email that Audio.TST is sent to). You’ll be prompted to add a password, confirm it, and you’re done.
You’ll notice a new tab on Site Registration Services called “Downloads”. This tab lists all the files you’ve ever downloaded from AP.com, all saved in one convenient location. If you’re having any trouble at all with the new registration system, please email techsupport@ap.com.
Look for more resources at AP.com over the next two months.
Meet AP: Jim Williams
Jim Williams is one of AP’s senior application support technicians. When he’s not helping you with your 2722 tests, he’s blowing sax or recording local Portland jazz bands.
Important stuff first, what kind of sax do you play?
It’s a Yanagisawa. I started playing right when Pink Floyd’s Dark Side of the Moon came out, in the early seventies. There was a cut on the album that featured the tenor sax and I fell in love with the sound. |
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What’s your audio background?
I started off working at Yamaha’s National Factory Service dept. in the Pro Audio division, then I spent several years as a systems engineer with the UltraSound, one of the largest touring sound systems in the world. I’d always used Audio Precision gear; I even bought my own System One in 1989. So when I moved to Portland in 1996, AP was a good fit.
Who are the people who call for tech support?
We get a lot of design engineers, production test guys, field service… everyone really. We often get installation or driver configuration questions from new users, then I help more experienced users find more efficient ways to get what they need done.
What’s your specialty at AP?
I do a lot of automation programming, PSIA work, LabVIEW, GPIB. Even though I’ve been here nearly 10 years, I’m constantly amazed by what you can do within APBasic. We’re always finding new and better ways to use the integrated development tools.
What do you like most about working at AP?
We have a lot of freedom here to create new applications & find unique solutions for our customers’ problems. I’m very excited about the possibilities of the new APx585 multichannel analyzer. The new interface is going to let customers get the job done a lot quicker and easier.
What are some of your best moments at AP?
There was a time when I was called down to large venue in Las Vegas. The sound system had intermittent dropouts and they couldn’t find the problem, I went down there with an ATS-2 and using INTERVU to look at the eye pattern, we found that a single digital audio cable had been pinched during the installation. It’s amazing that a multimillion dollar sound system can be compromised by one lousy cable. But we found it, fixed it and saved the day.
If you have a large venue in Vegas with internittent dropouts, or just a driver you can't update, you can always contact Jim Williams or any of our other support engineers at techsupport@ap.com.
Events
AP Technical Seminar | Korea | Sept 4-5
Bruce Hofer will be hosting a series of technical seminars in Korea in September.
Email sales@ap.com for more info if you'd like to attend.
International Broadcasting Convention (IBC) | Amsterdam | Sept 8 - 12, 2006
RAI Convention Centre
Stand #: 8.168
http://www.ibc.org
AES Netherlands Section | The Netherlands | Sept 12
Bruce Hofer will be the featured speaker at the AES Netherlands Section meeting during the evening of September 12.
Email sales@ap.com for more info if you'd like to attend.
Audio Engineering Society (AES) | San Francisco | Oct 6 - 8, 2006
Moscone Convention Center
Booth #: (not yet assigned)
http://www.aes.org/events/121
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