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Audio Precision sends out the Audio.TST newsletter once a month to approximately 13,000 audio engineers and other audio professionals. Each issue looks at current events in audio test, answers readers´ technical questions and announces any AP news.

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audio.TST July 2006

Notes from the Test Bench
Output
Sound Advice
Test Results

Notes from the Test Bench

By Bruce Hofer, Chairman & Co-Founder, Audio Precision

Hello and welcome to the July issue of Audio.TST.

Summer has arrived, and it is hot. The sky is clear blue and we're experiencing record temperatures here in Oregon. This is a good thing, except when the sun glares across my monitor.

But back to audio. Read on for a review of how to connect AP software to a database and some background on pre-analyzer filters, and don't forget you can always email us with your own questions at audioTST@ap.com.

I hope you are enjoying the summer and if you're attending IBC Amsterdam in September or AES San Francisco in October, we look forward to seeing you soon.

Bruce

Output: Tech tips and new applications from AP

Exporting AP Measurement Results to a Database in AP2700

We often get requests for information on how to export test results directly from AP software into a third party database. This can be done relatively easily through an AP Basic macro run inside AP2700 software. All that's required is Windows XP and an MS Access data file ready to receive the data export from the AP software.

Follow the below instructions to set up your AP2700 to a database

1. Set up the measurement you wish to take.

Start up AP2700 on your computer.
Connect the device under test.
Set up the measurement parameters inside the AP2700 software.

2. Create an MS Access data file on your computer.

Create names for each field by mapping the columns from the AP2700 data editor to the columns in the database table.
Refer to your database's help file for instructions on how to do this.

3. Create and save the Macro using the template below.

Go back to AP2700.
Open the Macro menu and chose "Open Panel".
Copy the below script into the Panel.
Edit the line ""C:\Your_Folder\Your_dbase.mdb"" so it maps to the location of your data file.
Make sure the macro's column parameters units (e.g.: Hz and %) match the settings in the AP2700 software.
Save the macro in a folder of your choice (defaults to AP2700 folder).

4. Run the macro from inside AP2700.

Go to File / Open / Macro and browse to the macro you saved.
Open the macro and run it.
You will be prompted to name the measurement or instrument you're testing. This name will be added to the data file so you can identify this acquisition later.

The Macro will take the measurement you set up in Step (1c) and then automatically export the acquired data into the data file you specified in Step (3d).

You can now repeat the process to add more measurements to the data file or use the Microsoft ODBC protocol to allow your preferred database manager to analyze the results as needed, for example plotting standard deviation to indicate production run quality.

 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

            ' AP BASIC DATABASE CONNECTIVITY EXAMPLE

            ' Audio Precision Tech Support 

            

            ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

            ' Macro Description:

            ' This macro shows how to use the Microsoft DAO (Data Access Objects) 

            ' collection to connect AP Basic to an MS Access Dbase

            ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

            Sub Main Dim DBEngine As Object

            Dim DB As Object

            Dim RS As Object

            Dim FreqArray As Variant

            Dim AmplArray As Variant 

            

            --- These commands load the activex DAO object ------

            

            Set DBEngine = CreateObject("DAO.DBEngine.35")

            DBEngine.SystemDB = "C:\Windows\System\system.mdw"

            DBEngine.DefaultUser = "NewUser" 

            DBEngine.DefaultPassword = ""

            DBEngine.CreateWorkspace("JetWorkspace", "admin", "",2) 

            

            'Make MS Access Connection

            Set DB = DBEngine.OpenDatabase("C:\Your_Folder\Your_dbase.mdb")

            Set RS = DB.OpenRecordSet("SweepData")

            

            '--- Input your test conditions (product, serial no. etc.) 

            

            Product = InputBox("Enter Product") 

            SerialNo = InputBox("Enter Serial Number")

            AP.Sweep.Start

            

            Length = AP.Data.ColSize(0,0) '<--- returns the number of rows in the sweep 

                          

            FreqArray = AP.Data.XferToArray(0, 0, "Hz") '<--- Your column parameters 

            AmplArray = AP.Data.XferToArray(0, 1, "%") '<--- Units must match instrument state.

                          

            For i = 0 To length -1 '- iterate rows mapping sweep data columns to fields

            RS.AddNew

            RS!Product = Product

            RS!SerialNo = SerialNo

            RS!SweepIndex = i

            RS!Column1 = FreqArray(i)

            RS!Column2 = AmplArray(i)

            RS.Update

            Next i 

            

            RS.Close 

            

            End Sub

As always, AP Tech Support is available at ap.com/contacts 5 days a week to help with any instrument questions you have. Just email us if you need help customizing this script for your particular needs.

Sound Advice: Audio Test Q&A

Q: When would I need a pre-analyzer filter?

A: In conventional audio analyzers, signal filtering is implemented late in the measurement path, following several analyzer gain stages. This approach provides repeatable and accurate results for devices whose noise spectrum is somewhat constant or diminishes slightly with frequency, typical of a wide range of audio devices. Audio Precision's analog analyzers and DSP-implemented analyzers follow this model.

However, the output signal from some devices can exhibit high levels of energy at high frequencies beyond the audio band. This is characteristic of digital-to-analog converters (DACs) and switch-mode or Class D amplifiers outputs. This high-level out-of-band energy can overload analyzer input stages and produce inaccurate measurements.

To reduce this out-of-band energy before the signal is applied to the analyzer input circuits, we recommend using a low-pass pre-analyzer filter.

The S-AES17 pre-analyzer filter for DAC testing
The Audio Engineering Society has published its recommendations for the measurement of digital audio equipment in the document AES17. Recognizing the problem in measuring signals in the presence of out-of-band noise, AES17 recommends the use of a pre-analyzer filter when measuring DAC outputs.

The Audio Precision S-AES17 pre-analyzer filter option satisfies the recommendation in AES17. The filter is comprised of two components: a low-pass filter module inserted before the analyzer gain stages, and a "brick-wall" low-pass filter inserted later in the measurement path.

S-AES17 is a factory-installed internal option for analog-equipped System Two and 2700 Series instruments. An S-AES17 kit is available for field installation.

The AUX-0025 filter for switch-mode amplifier testing
The Audio Precision AUX-0025 is a two-channel low-pass pre-analyzer filter mounted in a 1U standard rack mount chassis. AUX-0025 can be used with any Audio Precision analyzer that has analog inputs, including System One, System Two, the 2700 Series and the ATS-2.

The AUX-0025 has been carefully designed to reduce switch-mode (Class D and other) amplifier out-of-band noise before the signal is applied to the analyzer inputs. The filters in the AUX-0025 use custom-wound inductors that are optimized for extremely low distortion at the levels and impedances typical of amplifier outputs.

Test Results: AP News & Events

AP News

Amplifier Technologies, Inc. (ATI) is the first manufacturer to employ the APx585 multichannel audio analyzer in a production environment.

ATI has been making multichannel amplifiers since 1992 and has been using AP instruments in their R&D and production-line test for many years before that.

ATI is known for their dedication to quality control and superior performance parameters. With the APx585, ATI will be able to continue engineering and manufacturing more complex channel-intensive products, without compromising speed of production. The APX585 will be key to more efficient testing of new products under development and will help assess readiness for Dolby and DTS compliance certification.

"We've been looking for a multichannel audio analyzer to speed up our R&D and production line test ever since we started making multichannel amps in 1992," said Morris Kessler, president of ATI. "The APx585 has hit the nail on the head for multichannel capability and ease-of-use."

Read the whole press release: ap.com/press

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