Tech Notes


Technote 127: Leveled Acoustic Output (1.14 MB)

Technote 127: Leveled Acoustic Output, PDF only. To test acoustic input devices like microphones and hearing aids, users typically want to stimulate the device under test (DUT) with an acoustic signal at a specified sound pressure level (SPL). In addition, to measure the frequency response of acoustic devices, it is desirable to create a sound field that has the same sound pressure level over a wide range of frequencies. This is sometimes referred to as "€œleveled acoustic output."

Technote 128: Speech Transmission Index Measurement with APx Audio Analyzers (460.10 KB)

This TechNote discusses STI measurement, including the different methods identified in IEC 60268-16, a brief comparison of STI versus PESQ and/or POLQA perceptual audio testing, and finally a full discussion of STIPA method-based measurements using an APx500 Series audio analyzer and Audio Precision's STI measurement plug-in.

Technote 129: Production Test with APx Audio Analyzers (1.1 MB)

This Technote examines the automated test capabilities built into the APx500 measurement software, with emphasis on features recently added in release v4.2 to support production test of electro-acoustic devices. TN129 also provides a practical example, specifically the configuration of APx for production test of loudspeakers, and includes discussion of "golden units" (reference devices), input equalization, multiple sequences in a single project, and Production Test mode.

Technote 12: Creating Arbitrary Waveforms Using Time Record data (20.14 KB)

System One DSP can produce signals based on a stored waveform loaded into its memory. A file with a .wav extension is downloaded to the DSP memory in System One to create the output. A utility called MAKEWAVE.exe is supplied With System One DSP that will convert an ASCII file that contains a time record into the .WAV format for use with the DSP generator. This Technote describes the format of the .waa ASCII files and how to create arbitrary waveforms. It assumes some programming knowledge.

Technote 130: Measuring Audio-Video Sync with APx Audio Analyzers (448.0 kB)

TechNote 130 discusses how to make A/V sync measurements using an APx500 Series audio analyzer and Audio Precision's A/V sync plugin. This downloadable file is only the technote PDF.

Please use the link below to download a zip file containing the plugin and technote.

Technote 131: Measuring AGC with APx Audio Analyzers (442.0 kB)

TechNote 131 discusses the fundamentals of automatic gain control (AGC), how to measure AGC in hearing aids and other audio devices using the APx attack-and-release measurement plugin, and how to make other, related performance measurements. This downloadable file is only the technote PDF.

Please use the link below to download a zip file containing the plugin and technote.

Technote 132: Fractional Octave Analysis with APx Audio Analyzers (417.0 kB)

TechNote 132 discusses fractional octave analysis and introduces Audio Precision's octave analysis plugin for use with APx500 Series audio analyzers. This downloadable file is only the technote PDF.

Please use the link below to download a zip file containing the plugin and technote.

Technote 13: PC Sound Card Testing Using DSP-RIFF.exe Waveform Conversion Utility (481.53 KB)

The multimedia expansion in the PC industry has created the need to test the audio performance of sound cards. This is a classic dual-domain application requiring testing of the D-to-A and A-to-D sections. This utility will translate either direction between the Microsoft RIFF .WAV file format and the Audio Precision DSP.WAV file format. This allows a System One test signal created by MAKEWAVE to be played back though the D-to-A, and a captured PC .WAV file to be analyzed on System One.

Technote 14: Testing Reduced Bit-Rate Codecs Using the System One DSP Program CODEC.dsp (1.14 MB)

Reduced bit rate codecs cannot be properly tested using conventional sine wave test signals. Using multitone test signals and FFT analysis, the codec can be stressed to properly characterize how it will perform with program material. CODEC.dsp uses multitone testing techniques and internal automatic masking curve generation to facilitate objective and repeatable evaluation of codecs.

Technote 15: GPIB Communication from AP Basic (739.31 KB)

This Technote describes how to setup communication between AP Basic and GPIB instrumentation (using the National Instruments GPIB Interface.)

Technote 17: Computing THD Measurements from FFT Data Using THD.exe (47.91 KB)

Conventional analog total harmonic distortion tests are made with a notch filter that removes the fundamental and makes a root sum square summation of all of the harmonics. FFT techniques, on the other hand, provide the absolute amplitude of each individual harmonic. This program will extract the necessary harmonic data and the fundamental amplitude, compute the rss summation and express the result as a conventional THD ratiometric value.

Technote 18: Multitone Waveform Creation Utility for Use with FASTTEST (159.31 KB)

This Technote describes the Makewave utility, an AP Basic procedure that simplifies the process of creating multitone waveform files to use with the analog and digital generators in System One and System Two instruments. The download includes the utility.

Technote 1: Generating Impedance vs. Frequency Plots with System One (53.06 KB)

Describes how to generate Impedance versus Frequency swept data using System One. This is of particular interest to loudspeaker designers where the impedance response can provide very useful information on the performance of a speaker. Includes a BASIC program that does the calculations.

Technote 27: Polarity Test Procedure (90.00 KB)

This utility determines the signal polarity between the Analog Generator Outputs and the Analog Analyzer Inputs. A common error in manufacturing of loudspeaker systems is to connect voice coils with reversed polarity. Even when all drivers in a multi-way system are phased correctly with respect to one another, it is possible to have the interior wiring to the external connection terminals of the cabinet reversed. An individual driver reversed will cause a dip in frequency response near the crossover frequency to the adjacent driver, since the two speakers are then producing acoustical output of nearly identical amplitudes but out of phase. An entire system wired out-of-phase would presumably be undetectable in a monaural application, but unacceptable in stereo systems. With minor adjustments, this procedure can be run as a stand-alone test, or it can be incorporated into other test setups. The procedure can test a single path, or it can test stereo channels. Equipment required is DSP or Dual-Domain version of System One, System Two, or System Two Cascade, and a microphone if you are testing acoustic paths such as loudspeakers.

Technote 28: Measurement Microphone dBSPL Calibration (175.50 KB)

This Technote describes how to set up and use the dBr unit as dBSPL. Automated AP Basic macros (procedures) are available to facilitate the calibration. These macros apply to the instrument analog analyzers. Additionally, two computational methods are described to help you understand the macros, and to help you calibrate a measurement microphone without the macros.

Technote 29: Computing Group Delay from Phase Data Using APWIN (435.00 KB)

Group delay is a property of a device or a system: a plot of the change in phase of the response as a function of frequency; it is the negative derivative (slope) of the phase-vs-frequency characteristic of a device. Constant group delay across the frequency band means that all portions of a wideband signal arrive simultaneously. A pure time delay, equal at all frequencies, gives a level straight-line plot of phase versus frequency. In an audio component, this plot may vary with frequency, and the component is said to produce group delay distortion. Group delay is of interest to audio engineers, particularly in the design and test of low-pass filters used in digital audio and in loudspeaker design areas. For instance, an anti-aliasing filter will typically have a phase response curve which slopes sharply down at high frequencies. This means that the high-frequency components will be delayed longer in their passage through the filter, resulting in a loss of precision in musical transients and a more diffuse stereo image. It is possible to correct the group delay distortion of such filters by using an all-pass network, but this is seldom done in practice.

Technote 30: WAV file Import (163.50 KB)

This APWIN utility allows you to load any .wav files compatible with the Microsoft RIFF file format into APWIN and analyze them in the frequency or time domain.

Technote 3: Remote Site Data Retrieval of Test Results Using Modems 1.0.0 (0.00 KB)

Some measurement situations place the measurement equipment at some distance from the operator. Many broadcast applications require that System One be located at a distant, possibly unattended site. This Technote describes how to set up a modem communication link between the distant measurement PC and a local operator PC to enable manual or automatic transfer of measured data. The set up for two commercial communication programs, PC Tools Commute and Norton pcAnywhere, are described.

Technote 4: Computing Equalization Curves Using EQCURVE.EXE (41.00 KB)

Tests of recorded or transmission media often require an equalized generator signal. Modifying the response of a swept generator to reciprocate the pre-emphasis or de-emphasis characteristics of the device under test will prevent overload and yield a flat response at the output. This Technote includes a BASIC program that will compute a data file based on user supplied time constants. The data file can then be used as an S1.exe EQ curve.

Technote 5: Usage Instructions for COMBINEC.EXE (34.00 KB)

System One produces data files that are two or three columns wide with as many rows as measurement steps. Usually the first column is the source data and columns two and three are measured data. There are some applications where it is desirable to use some data from one file with data from another file to produce a third file. This Technote includes a C program that allows columnar data to be exchanged, moved or combined to produce a new data file.

Technote 6: Computing Statistical Data From Nested Sweeps Using NSWEEP.exe (42.00 KB)

When several plots of a parameter are acquired, it is often useful to reduce the large volume of data to statistical summaries such as maximum, minimum, average or delta. This Technote includes a program that will operate on an S1.exe nested sweep file to produce the statistical data mentioned above. The program can be run in an S1.exe DOS shell.

Technote 7: Programmers' Reference to S1.exe internal *.tst file format 1.0.0 (0.00 KB)

S1.exe *.tst files save instrument setups and test data in a binary format for space and speed efficiency. It is possible to examine such a file (or *.lim, *.eq, *.swp and *.ovl files) to extract this data. This Technote explains the internal structure of these files. It assumes intermediate programmers knowledge and is intended as a reference source, not a step-by-step explanation.

Technote 8: Programmers' Reference to S1.exe DSP Waveform File Format 1.0.0 (0.00 KB)

System One DSP programs allow a SAVE WAVEFORM operation to store the time record data to disk. This Technote describes the internal structure of the *.wav files so produced. This would allow a knowledgeable programmer to extract data from this file for external post processing. It assumes intermediate programming expertise.

Technote 9: Restructuring Multitrack Data Using MTRACKFR.exe (43.00 KB)

Frequency response measurements on a Multitrack tape recorder are best made by successively measuring each track at the first frequency, then step to the second frequency and measure all tracks, and so on until all frequencies are measured. This produces a nested sweep file that plots amplitude versus track rather that amplitude versus frequency. This Technote contains a program that will restructure such data into the preferred format