Audio.TST Archive

I'm tied up in new projects right now (more on that next time), so I'm going to hand over this month's Notes to AP CEO Alan Miksch. Have a good holiday, and happy new year.
PS: There's a little Christmas present from AP in Sound Advice below. Enjoy.

-- Bruce

2006 in Review
By Alan Miksch, AP President & CEO

2006 will always be remembered as the year we launched the APx.

It was hard to keep the project quiet, especially when customers have been asking for the exact features we've been working on, but it was essential that we wait until we had a shippable, sellable product that could stand on its own before we announced. Three years of development is a substantial investment for any business, but looking at the tremendous growth and rampant diversification of audio into all sorts of applications, it's clear that we in test and measurement can't just continue to offer the same solutions that worked ten or even fifteen years ago.

Yes, the dual domain 2700 Series will continue to lead the industry in terms of performance & flexibility for at least two to three years, but in terms of the next generation of innovation, it's the APx family.

2007 will have its own milestones. Expect to see new APx models addressing different segments of the audio market, and look for an expansion of our service support around the globe. In June we'll mark the five year anniversary since the last System One rolled off the production line. System One put AP on the map, and it has been a workhorse that tens of thousands of audio engineers have relied on to create some of the finest audio equipment the world has ever seen. As part of our product support policy, we're still committed to servicing System One until June, but after that we can't guarantee our service capability. Already parts are getting harder to find, and the day will come when we can no longer make the repairs to keep the instruments in serviceable condition.

Thank you all for your continued support of AP, and we look forward to seeing more of you out on the road at tradeshows and customer seminars -- be sure to stay tuned for new announcements. I hope you too had a good year, and here's to the next one being even better.

Alan Miksch
President & CEO

Question:
What is the difference between unbalanced ground (GND) and unbalanced floating configuration for the analog generator in System Two and 2700 series instruments?

Answer:
System Two family instruments have a transformer coupled output. In the unbalanced ground configuration pin 2 of the XLR, the center conductor of the BNC, and the + banana jack connect to the top end of the output transformer through the selected output impedance. The center tap of the transformer connects directly to pin 3 of the XLR, the shell of the BNC, and to the minus banana jack. If the output configuration is selected as ground, that common conductor is also connected to ground through a PTC protection device.

Question:
How can I measure Dynamic Range using an APx585?

Answer:
Dynamic range is the ratio between the full scale output of a device and the spurious noise products created when the device is producing a very low level signal. It is a commonly made measurement for DAC's, ADC's, and other digital audio devices.

Dynamic range is usually measured by stimulating a device with a full scale sine wave and measuring its output level, then stimulating the device with a sine wave that is -60 dB below full scale and measuring the level of the noise and distortion products that remain after the fundamental is removed from the output of the device with a notch filter. The dynamic range is the ratio of the two, usually expressed in dB.

You can make this measurement with an APx as follows:

1. First, configure the connections to the device under test using Signal Path Setup. APx585 can work with any combination of digital or analog, input or output devices.
   
   
2. Switch to the Reference Levels view to find the full scale output level for the device:
   
   1. If the device has a digital input, stimulate the device with a 0 dBFS signal and set the input reference dBrA to the device's output level. If the device has adjustable gain, you would normally adjust the gain until the output is just below clipping. You can find this level using the "Scope" or time domain signal monitor view.
   2. If the device has an analog input, adjust the generator level until the output clips, or (for digital outputs) reaches 0 dBFS. Now set the generator reference dBrG to the generator level and the input reference dBrA to the device's output level.
      
      
3. Now switch to the THD+N Level result in the THD+N measurement view:
   
   
   1. If the device has a digital input, set the generator to -60 dBFS. If the device has an analog input, set the generator to -60 dBrG.
   2. If desired select a low pass bandwidth limiting filter (20 kHz is the default) and a THD+N weighting or high pass filter.
   3. Set the units in the THD+N level result to dBrA.
   4. Turn the generator on. The absolute value of the measurement is the Dynamic Range of the device. For example, if the measured result is -90 dBrA, you would report a Dynamic Range of 90 dB.
      

Question: What Christmas present can you get for the Audio Engineer who has everything ? Answer: An AP Ringtone! www.ap.com/ringtone

Yes. AP has created two ringtones for your cell phones and made them available for download from the AP website. Just go to www.ap.com/ringtone to listen to the tones and get them sent to your phone or download direct from the site. There's no charge and no obligation, just a little Christmas cheer from all of us at AP. We look forward to hearing lots of sweeps at the next tradeshow.

About the Tones

Logarithmic frequency sweep
Logarithmic frequency sweep or "Chirp" is the new signal analysis technique Audio Precision developed for faster audio test. It is based on the work Dr. Angelo Farina of the University of Parma introduced at AES in 2000. AP has taken this theoretical research and married it with our practical experience to make the fastest audio analyzer in the industry, the multichannel APx585.

Chirp takes a single sweep through the entire audible spectrum from 20 Hz to 20 kHz, then pushes the signal through some complex math to derive all the standard audio measurements. Where this new chirp stands out is it increases the speed of the sweep exponentially over time so the acquisition is much faster. In fact, with this chirp technology, the APx585 can take 14 standard measurements in 14 seconds across 8 channels of audio -- all with one mouse click.

And it sounds cool too.

Multi-tone
It's not quite Christmas bells, but a multitone will certainly get your attention.

Audio Precision has perfected the use of multi-tone stimulus signals for specific applications. A multi-tone is an audio signal that contains several sine waves of different frequency. The precise characteristics of the signal are provided by the multi-tone generator to the multi-tone analyzer, which acquires and processes the signal using FFT analysis. One multi-tone acquisition can provide DC offset, frequency response, phase response, THD spectrum, noise spectrum and crosstalk results simultaneously, bringing a great speed advantage.

AP uses a multi-tone in its High Speed Tester (HST), an Audio Precision application that gives you simple tools to easily set up comprehensive tests for personal media players, and then quickly and reliably test against limits in a production environment. Read the AP High Speed Tester Technote to learn more about how HST can improve your production test efficiency.

System One Service Manual now on the web

Over the next six months, we will be winding down System One support. By popular request, we have posted the System One Service Manual on the AP website. The download includes a PDF of the original Service Manual as well as various test files, Perf check and other troubleshooting tools.

ap.com/products/legacyproducts

Disclaimer: This System One Service Manual has been distributed by Audio Precision as a courtesy, without warranty of any kind, free-of-charge to qualified technicians wishing to adjust, service and/or repair System One instruments. Please be mindful that if you use this Service Manual to adjust, service and/or repair your own System One instrument, Audio Precision does not support or warrant its contents and/or use in any way.

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