AP - The Recognized Standard In Audio Test



AP’s built-in PDM option provides direct I/O, modulation, and decimation for powerful test and analysis of PDM devices from bitstream to embedded audio with no unnecessary conversions or hardware getting in the way.


Pulse Density Modulation (PDM) is a one-bit, high rate data stream that conveys a signal by modulating the density of the pulses. A typical application for PDM is the Micro-Electrical-Mechanical System (MEMS) microphone found on smartphones.

The APx PDM option provides direct connectivity for audio devices that have a PDM output (such as a MEMS microphone) or input (such as the decimator on a smartphone chip). In addition to all the standard audio measurements, APx provides variable DC voltage, variable sample rate, and a PSR (power supply rejection) measurement to test the device’s full operating parameters. No other analyzer combines direct PDM connectivity with APx’s best in class speed, ease-of-use, and performance.

Comprehensive audio test from the recognized standard

PDM (mono or stereo) can be selected for both the analyzer inputs and outputs simultaneously, or PDM can be paired with any of the other available I/O formats: analog (bal/unbal), AES or S/PDIF digital, Bluetooth, HDMI, or serial digital. Over 30 one-click audio measurements may be made, either individually or in an automated project. Features include weighting filters, and user defined high and low pass filters, one-million-point FFTs, real-time oscilloscope monitoring, custom reports, statistical calculations, and quasi-anechoic acoustic measurements.

Wide range of clock rates and interpolation/decimation ratios

When APx is the clock master (the typical use case for measuring a MEMS microphone), the clock rate is continuously variable from 128 kHz to 24.576 MHz, with an accuracy of 3 ppm. This supports sample rates from 4 kHz to 192 kHz, with interpolation/decimation ratios of 32, 33.33, 37.5, 42.67, 48, 50, 64, 66.67, 75, 85.33, 96, 100, 128, 150, 192, 200, 256, 300, 384, 400, 512, 600, 768 and 800. The same clock range is accepted by APx when the external device is the clock master. Both input and output can be configured as a master or slave independently, and the built-in modulator can be set for 4th or 5th order operation.

Built-in power supply and PSR testing

The logic level and external power supply voltage are variable in 0.1 V steps from 1.5 Vdc to 3.6 Vdc, allowing testing beyond the range of typical devices. Additionally, AC signals can be added to the external power supply, allowing automatic measurement of power supply rejection (PSR), with support for 217 Hz square waves and adjustable duty cycle for GSM devices.

Analyze complete PDM bitstream


Unique in the industry, the APx PDM option allows engineers complete access to the undecimated PDM bitstream via FFT analysis. Issues with modulators or unwanted aliasing can be quickly identified and addressed alongside audio passband measurements.

Fast and intuitive UI

PSRR graph

APx500 software is the industry standard for clarity, speed and ease of use. Measurements and are organized within projects that can be saved, edited and shared. The results browser gives engineers a comprehensive view of all available measurements within a category so that issues can quickly be identified. Absolute and derived results are always available for all datasets.

Automation and sharing data

Complex test sequences can be created within the UI, or the APx API can be accessed for full control from any .NET application or LabVIEW. Graph results are stored within the project, and projects can be locked before sharing with contract manufacturers or other partners.

Rich reports with color graphs and pass/fail results can be generated automatically using default or customized Microsoft Word templates.

Isolation of audio stages

With APx, nearly any combination of input and output can be measured directly: Bluetooth, analog (2, 4, or 8 channels), AES3 or S/PDIF digital, I2S digital serial, and HDMI are all available.

Quasi-anechoic acoustic test

HATS manekin

Most PDM devices have PDM at one end of the audio chain and a transducer at the other. APx’s Acoustic Response measurement makes 14 key acoustic measurements in 3 seconds and uses an energy time curve to find the ideal time gate quickly and easily.

DSD testing

The APx PDM Option can be used to test and measure DSD (Direct Stream Digital) and DSD128 devices, as both transmitter and receiver. DSD is the format used on Super Audio CDs (SACD).


Key features

  • Direct connectivity to any device with a PDM input or output
  • FFT analysis of undecimated PDM bitstream
  • Vdd adjustable from 1.5 to 3.6 Vdc
  • Built-in PSR testing
  • Support for over 20 different interpolation/decimation ratios from 32x to 800x
  • 4th or 5th order delta-sigma modulation
  • Multiple I/O interface options: PDM, analog balanced/unbalanced, AES3 and S/PDIF digital, HDMI, Bluetooth, and serial digital
  • A flexible, intuitive UI with over 30 one-click audio measurements
  • Powerful “code-free” built-in automation
  • API for VB .NET, C#, or LabVIEW automation and control
  • Custom reports using Microsoft Word templates or output to database
  • Compatible with APx520, 521, 525, 526, 582, 585 and 586

For more information see APx PDM Option Technical Details


Download PDM Datasheet

  • Sample Rate Range
    4 kHz to 192 kHz
  • Clock range
    128 kHz to 24.576 MHz
  • Oversampling ratio
    32, 33.33, 37.5, 42.67, 48, 50, 64, 66.67, 75, 85.33, 96, 100, 128, 150, 192, 200, 256, 300, 384, 400, 512, 600, 768 or 800
  • Modulator
    4th or 5th order
  • Interface logic levels
  • Edge modes
    Rising edge, I channel; Falling edge, 1 channel;
    Stereo (Both edges), 2 channel
  • Vdd
    1.5-3.6V, 15 mA


  • Modulator maximum input level
    –0 dBFS
  • SNR
    129 dB (1 kHz, 20 kHz BW, unwtd, 256x oversampling, 5th order modulator)
  • THD+N
    –129 dB (1 kHz, –9.3 dBFS, 20 kHz BW, 256x oversampling, 5th order modulator)
  • Dynamic range
    137 dB (AES17, CCIR-RMS, 256x oversampling, 5th order modulator)
  • Flatness
    ± 0.001 dB (20 Hz to 20 kHz)
  • Connectors
    Output data, output clock, input data, input clock,
    external power (all via BNC)

Download full APx525/582/585 family specifications

  • Residual THD+N (20 kHz BW)
    –105 dB + 1.3 µV [APx525]
    –103 dB + 1.4 µV [APx585]
  • Sine Frequency Range
    0.1 Hz to 80.1 kHz [APx525]
    5 Hz to 80.1 kHz [APx585]
  • Frequency Accuracy
    2 ppm [APx525]
    3 ppm [APx585]
  • IMD Test Signals
  • Maximum Amplitude (balanced)
    21.21 Vrms [APx525]
    14.4 Vrms [APx585]
  • Amplitude Accuracy
    ±0.05 dB
  • Flatness (20 Hz–20 kHz)
    ±0.008 dB
  • Analog Output Configurations
    unbalanced & balanced
  • Digital Output Sampling Rate
    22 kHz–192 kHz
  • Dolby / dts Generator
  • Maximum Rated Input Voltage
    300 Vrms (bal) / 160 Vrms (unbal) [APx525]
    110 Vrms (bal/unbal) [APx585]
  • Maximum Bandwidth
    >90 kHz
  • IMD Measurement Capability
  • Amplitude Accuracy (1 kHz)
    ±0.05 dB
  • Amplitude Flatness (20 Hz–20 kHz)
    ±0.008 dB
  • Residual Input Noise (20 kHz BW)
    1.3 µV
  • Individual Harmonic Analyzer
  • Max FFT Length
    1024K points
  • DC Voltage Measurement

  • PC with 2 GHz or faster processor, 2 GB or more RAM
  • Microsoft Windows XP (32-bit, SP 2 or later),Windows Vista (32-bit), Windows 7 (32 or 64-bit) or Windows 8 (32 or 64-bit).
  • System performance is sensitive to processor speed; faster processors will yield faster results.
  • APx500 is data intensive and it is recommended that other data-intensive applications not be run concurrently. This includes Audio Precision AP2700, APWIN, or ATS.

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