[jude]

I think we're going to start seeing a lot more Audio Precision measurements soon, from a lot more people.

At the center of our measurement lab at Head-Fi is an Audio Precision audio analyzer. Whether we're measuring headphones or electronics, the Audio Precision analyzer and its companion APx500 software generates the stimulus signals we run through the device under test (the DUT), and then resolves the differences between those signals and the DUT's output to generate countless different measurements.

What's so democratizing about APx500 is that it allows someone who is not an engineer by trade (like me) to run very advanced analysis of audio gear of all types (both electronic and acoustic) without scripting or coding. And despite its ease of use, it is still considered the highest standard in the industry for audio analysis. Every audio engineer I know either uses Audio Precision or wants to.

With the help of APx500 I came up with a headphone placement method (for headphone measurements) that I've been sharing with headphone engineers. Again, I'm not an engineer by trade, but APx500's easy multi-instrument views even enabled a relative pleb like me to come up with this novel technique. (We'll be posting a video of the latest version of this procedure soon.)

If there's been a problem with Audio Precision APx500 software, it's that you needed to have an Audio Precision hardware audio analyzer to use it -- and that can be an expensive proposition for smaller companies and measurement enthusiasts.

That has now changed. Recently, Audio Precision decided to make their APx500 software suite available to use with the ASIO-capable audio interface of your choice, and it's called APx500 Flex, and comes with something called an APx500 Flex Key. From Audio Precision's APx 500 Flex page:

The APx500 Flex audio analyzer—comprised of APx500 measurement software and an APx500 Flex Key—allows you to select the ASIO-capable audio interface of your choice to use along with AP’s versatile and powerful APx audio measurement software. Start with the measurement options you need now, with the freedom to add additional measurements as your test requirements evolve. The APx500 Flex brings Audio Precision innovations such as one-click measurements, code-free automation and sophisticated reporting to off-the-shelf audio interface hardware solutions.

Across all measurements, the APx500 user interface is fast and intuitive. Just click to select a measurement, then click to add a filter. Drag limits to set pass/fail points right on the results graph. Effortlessly specify computations for derived results. Add defined measurements in a series and run them in an automated procedure called a Sequence. The APx generator can output steady tones, twin tones, sweeps, chirps, multitones, or play WAV files as arbitrary waveforms.

Repetitive bench tests and production testing can easily be automated with the built-in measurement sequencer and saved as a project that can be used with any APx analyzer. Production Test mode provides an optional simplified operator interface with multiple run statistics, created and supervised by a manufacturing engineer. Access the API if you prefer: documentation for VB.NET, C#.NET, MATLAB and LabVIEW is included.

Now while any ASIO-enabled audio interface should work with APx500 Flex, Audio Precision has verified the compatibility of the audio interfaces listed below, with configuration templates for these devices included in the APx500 software (version 5.0.2 and later):

• RME Fireface UC
• RME Fireface 802
• Lynx Aurora (n)
• Lynx E22

Again, though, any ASIO-enabled audio interface should work with Audio Precision APx500.

APx500 Flex Audio Analyzer software pricing starts at $3000 USD, and you can configure options and view pricing for it at the following link:

Audio Precision APx500 Flex Audio Analyzer​

Audio Precision also has incredibly knowledgeable support engineers available to help their customers. They've saved my hide countless times via telephone and email, walked me through measurements and procedures I hadn't previously thought of, and even updated their CSD module when we submitted a feature request for it.

If you end up using APx500 Flex, and want to discuss or share tips and tricks for headphone measurements, feel free to contact me here.

 

[MLGrado]

wow! Just coming when I needed it!!!! Was in market for one to use with my mothballed audio blog that I am about to bring out of hibernation. Well, in the market for some of the way cheaper options, til now! Never thought we could get our hands on AP software ever without breaking the bank, even if they won't be comparable really to measurements made by other people since the hardware will vary from person to person, at least now one can directly compare devices themselves relative to their own 'bogey' measurements.

 

[jude]

Here's a video from Audio Precision introducing APx500 Flex:

---

Here's a video about configuring APx500 Flex:

​

 

[miceblue]

What microphones are recommended to use with APx500 Flex and a USB interface of choice? I have a Focusrite 18i8, so I would assume the only thing I would need are measurement microphones and some sort of stand for the headphones to sit on reliably and reproducibly.

At least for headphone measurements. How does interfacing work if you want to, say, measure the performance of a DAC or amp?

 

[AudioTestDude]

What microphones are recommended to use with APx500 Flex and a USB interface of choice? I have a Focusrite 18i8, so I would assume the only thing I would need are measurement microphones and some sort of stand for the headphones to sit on reliably and reproducibly.

At least for headphone measurements. How does interfacing work if you want to, say, measure the performance of a DAC or amp?

Hi Miceblue - I am just joining this thread now and I saw your question. I do NOT recommend testing a DAC/amp with a sound card, whether it be Focusrite or any other brand. The reasons are as follows:

1. The sound card's own DAC and ADC sections will impart "distortion" that may skew the measurement results of what you're testing where you think that device's performance is worse than it actually is.

2. The output and input impedances of sound cards are not the same as those of an actual audio analyzer (for example the Audio Precision APx 555 used at Head-Fi). You want to make sure that the analog-input impedance of the measuring device is sufficiently high as to not load the analog output of the device under test (DAC in this case). The typical input impedance of a sound card is around 10 Kohms whereas an audio analyzer is 100K.

What can certainly be measured accurately is the frequency response using a sound card (as long as that sound card's frequency response if very flat). The APx Flex can allow one to make a frequency response of the measurement hardware (Focusrite 18i8 in your case) and use the inverse of this curve as an input EQ or correction curve. This is a technique used all the time to correct for the non-flat response of a measurement microphone when performing loudspeaker tests.

As far as using just a microphone to measure the headphones, this is not recommended because the headphone speakers need to "see" an acoustic impedance of that of a typical human ear. That is why Head-Fi uses specialized test gear such at the GRAS and B&K products.

I hope this helps.

 

[miceblue]

Hi Miceblue - I am just joining this thread now and I saw your question. I do NOT recommend testing a DAC/amp with a sound card, whether it be Focusrite or any other brand. The reasons are as follows:

1. The sound card's own DAC and ADC sections will impart "distortion" that may skew the measurement results of what you're testing where you think that device's performance is worse than it actually is.

2. The output and input impedances of sound cards are not the same as those of an actual audio analyzer (for example the Audio Precision APx 555 used at Head-Fi). You want to make sure that the analog-input impedance of the measuring device is sufficiently high as to not load the analog output of the device under test (DAC in this case). The typical input impedance of a sound card is around 10 Kohms whereas an audio analyzer is 100K.

What can certainly be measured accurately is the frequency response using a sound card (as long as that sound card's frequency response if very flat). The APx Flex can allow one to make a frequency response of the measurement hardware (Focusrite 18i8 in your case) and use the inverse of this curve as an input EQ or correction curve. This is a technique used all the time to correct for the non-flat response of a measurement microphone when performing loudspeaker tests.

As far as using just a microphone to measure the headphones, this is not recommended because the headphone speakers need to "see" an acoustic impedance of that of a typical human ear. That is why Head-Fi uses specialized test gear such at the GRAS and B&K products.

I hope this helps.

Thank you so much for the informative reply!