APx52x B Series Audio Analyzers

The ideal balance of analog performance and breadth of digital I/O.

APx52x B Series Modular, Two- and Four-Channel Performance Audio Analyzers

The APx525B Series is a two-channel audio analyzer for R&D engineers and production technicians who want fast and easy audio testing.



Multiple Simultaneous Input Types

APx500 software brings the multi-input capability to APx, allowing engineers to activate a second input type on any APx modular audio analyzer, or APx515 analyzer, and make measurements simultaneously on analog and digital signals.

This capability, paired with the highest channel count and widest range of digital I/O available, provides APx users critical cross-domain insight and the opportunity to reduce testing time. Watch a Multi-Input Demonstration

Common Software Platform

APx audio analyzers use a common software platform, making tests and results easier to share. All settings for a test are saved in a single project file, making it easy to replicate test setups between R&D and production facilities anywhere in the world. Project files are compatible with both B Series and legacy APx instruments and each project is self-contained, so there’s never any worry about dependencies or broken links. Users can even embed waveform files and images within a project file.

For sharing measurement results with customers, contract manufacturers or management, APx automatically generates rich graphic reports, with highlighted pass / fail limits and options to export as PDF, HTML, Excel, CSV, RTF or MATLAB files.

Transfer Function

The transfer function measurement provides the complex frequency response function for a device, including the magnitude and phase (or real and imaginary components), using any broadband signal.

This feature, a powerful addition to APx software’s Sequence Mode, allows any APx analyzer to be used as a multichannel dynamic signal analyzer or as a so called dual-channel FFT analyzer. With transfer function and any broadband signal, including speech, music or noise, APx users can now assess the complex frequency response, coherence, and impulse response of their device or system.

AP’s transfer function provides gapless and overlapped analysis of multiple acquisitions. It also includes a ground-breaking signal-based triggering that eliminates the need for a pilot tone in open-loop test applications, making it ideal for test of “smart” audio devices.

Jitter Analysis

Jitter in digital audio systems may cause audible distortion in the form of jitter sidebands in the output signal. Jitter tolerance testing can reveal jitter induced distortion but is often neglected in the design of circuits and components because it is difficult and time consuming. APx analyzers provide jitter generation and jitter analysis features to simplify jitter testing. Learn more

Digital Protocol Analysis

Modern consumer devices such as televisions, Blu-ray players, and receivers typically use a digital interface such as S/PDIF, Toslink, HDMI to transmit audio signals. In addition to the digital audio data, these interfaces also carry auxiliary information about the audio signal, metadata. The APx Metadata monitors decode and display metadata values as they are received from the device under test. Learn more

Open-Loop Chirp

This signal provides multiple, high-resolution results in a brief period of time and allows APx users to employ the chirp in test scenarios where the signal may originate, or terminate, as a file on the device under test (DUT) or on a server connected to the DUT. This new capability is especially helpful to those developing smart devices (e.g., smart speakers, smartphones).

Code-Free Automation and a Complete API

APx500 Measurement Software is the most advanced audio measurement interface available. Complex procedures that include user prompts, limits and calls to external applications can be created directly in the GUI, saving time and money while ensuring painless updates over time with no development required.

Create custom interfaces and application-to-application automation using the comprehensive APx API. Extensive documentation and examples are provided for Visual Basic.NET, C#, MATLAB, LabVIEW, and Python. Projects and automation can be shared with other APx units anywhere in the world.

Versatility in I/O

APx525 has two balanced and two unbalanced analog inputs and outputs plus 216k digital inputs and outputs via AES/EBU, TOSLINK and SPDIF. APx526 is the four-channel version of the APx525, developed for the four channel head units typical of the automotive audio industry.

Additionally, I/O may be expanded with optional Digital Serial (APx525 and APx526), HDMI + ARC (APx525), PDM (APx525 and APx526) and Bluetooth (APx525 and APx526) modules. Additionally, the optional Advanced Master Clock (AMC) module handles input and output clock signals to synchronize the APx52x Series with external equipment (or vice versa), and the AMC also enables jitter generation and analysis (in conjunction with Advanced Digital, Digital Serial or PDM modules).



High-Performance Options – AG52 and BW52
Developed for power amp designers, the AG52 analog generator option generates exceptionally clean square waves with a rise time better than 2 microseconds and has an improved THD+N of -110 dB (typical). The AG52 generates DIM 100, 30, and B square + sine waveforms and maximum output level is increased from 21.21Vrms to 26.66 Vrms (balanced).

The BW52 ultra-high bandwidth option offers advanced FFT performance: 1.248 million points, DC to 1 MHz bandwidth and full 24-bit resolution. Ideal for Class D amplifier design.

Advanced Digital I/O (option)
Provides AES3, AES/EBU balanced digital I/O on XLR; unbalanced SPDIF digital I/O on BNC; and TOSLINK optical digital I/O. The APx ADIO module enables the generation of advanced impairments for sophisticated test of devices via AES/SPDIF/TOSLINK. It also includes the Advanced Master Clock (AMC) module, which handles input and output clock signals for synchronizing an APx with external equipment (or vice versa). AMC also provides jitter generation and measurement functionality for jitter-enabled I/O modules such as ADIO, DSIO and PDM.

Advanced Master Clock (option)
The AMC module handles input and output clock signals to synchronize the APx52x B Series with external equipment (or vice versa). This module also enables jitter generation and analysis in APx500 Series analyzers with Advanced Digital (ADIO), Digital Serial (DSIO) or PDM modules installed.

ASIO (standard)
PC audio interfaces with installed ASIO drivers appear within the APx500 software as one of APx’s I/O options, with support for up to 16 bidirectional channels. All measurements and test sequences in APx may be used via the ASIO interface, allowing for complete characterization of the connected audio device.

Bluetooth Duo (option)

The Bluetooth Duo delivers a wider selection of A2DP codecs, faster pair and connection times, an increased feature set within APx500 measurement software, and improved RF shielding for use in production test environments. APx Duo supports Bluetooth core specification v4.2, HFP v1.7, HSP v1.2, AVRCP v1.4 and A2DP v1.3. Note: APx Bluetooth Duo requires v4.5 APx500 software (or later) and can only be installed on “Type E” APx chassis (manufactured after August 2012).


Bluetooth Legacy (option)
The Bluetooth module, with built-in radio and software stack, allows engineers to measure their Bluetooth devices directly. All Bluetooth controls are integrated into the analyzer software—APx supports A2DP, HFP 1.6, and AVRCP profiles. Codec support includes SBC, aptX, CVSD, and wideband speech (mSBC).

PDM 16 (option)
PDM 16 is an optional input module providing sample-accurate inter-channel phase information for up to 16 channels of pulse density modulated signals. With its acoustically-silent remote pod and extension cable preserving PDM signal integrity for up to 10 meters, PDM 16 readily supports MEMS microphone measurements in anechoic chambers. As an added feature, the module can provide up to 50 mA Vdd power supply to the device, or devices, under test.

PDM (option)
The Pulse Density Modulation (PDM) option provides direct connectivity for audio devices that have a PDM output such as a MEMS microphone, or an input such as the decimator on a smartphone chip. In addition to standard audio measurements, APx provides variable DC voltage, variable sample rate, and PSR (power supply rejection) measurements for testing devices’ full operating parameters. Jitter capable.

Digital Serial I/O (option)
Digital serial capability is essential in R&D for evaluating designs at the circuit board level. The Digital Serial I/O (DSIO) option provides a direct multichannel connection to chip-level interfaces such as I2S, TDM, and other popular serial interface formats including left-justified, right-justified, and DSP. Jitter capable.

HDMI2 + eARC (option)
The HDMI option allows engineers to measure HDMI audio quality and audio format compatibility on devices such as surround sound receivers, set-top boxes, smartphones, tablets, TVs and DVD or Blu-ray disc players. APx can stream both lossless and compressed formats from pre-encoded audio test files, making it easy to troubleshoot component compatibility and issues related to downsampling, downmixing, or transcoding.


APx500 software options provide measurements and functionality beyond the core set of capabilities standard for the APx52xB Series analyzers. A variety of options are offered, suited to different specific test applications and requirements.

For APx B Series analyzers, and legacy APx analyzers running version 5.0 software, software option licenses are electronically activated and are tied to a specific analyzer via serial number. For legacy APx analyzers running APx software version 4.6 or earlier, software option licenses are enabled by “iButtons” that mount on the rear of the instrument

Electroacoustic Production Test (SW-SPK-PT)
The SW-SPK-PT option enables high-speed production test of electroacoustic devices, providing key loudspeaker measurements in a single one-second sweep. Results include Rub & Buzz detection, essential Thiele-Small parameters, and impedance magnitude and phase. A proprietary modulated noise measurement is also provided to aid in detecting enclosure air leaks.

Electroacoustic R&D (SW-SPK-RD)
The SW-SPK-RD option delivers a complete suite of measurements and results tailored to the needs of designers and engineers developing electro-acoustic audio products. It includes key measurements and results such as complete Thiele-Small characterization; time-gated, quasi-anechoic Acoustic Response; Impedance analysis; plus the Loudspeaker Production Test measurements.

Perceptual Audio Test: POLQA (SW-POLQA-2)
Perceptual audio measurement returns a subjective assessment of speech quality using the next-generation POLQA algorithm for wide-band speech devices or devices with acoustic coupling. (Successor to PESQ with support for HD Voice, 3G, 4G/LTE and VoIP technologies)

Speech Intelligibility: ABC-MRT Measurement (SW-ABC-MRT)
The APx ABC-MRT plugin is a software option for APx500 audio measurement software that provides speech intelligibility measurement based upon the ABC-MRT speech processing algorithm developed by the Institute for Telecommunication Sciences (ITS) of the United States National Telecommunications and Information Administration (NTIA).

Speech Intelligibility: Speech Transmission Index (SW-STI)
SW-STI is a plug-in for conducting Speech Transmission Index (STI) measurements using the STIPA method.



  • Maximum Rated Input Voltage
    230 Vpk
  • Maximum Bandwidth
    >90 kHz
    >1 MHz [with BW52]
  • IMD Measurement Capability
  • Amplitude Accuracy (1 kHz)
    ±0.03 dB
  • Amplitude Flatness (20 Hz–20 kHz)
    ±0.008 dB
  • Residual Input Noise (20 kHz BW)
    1.3 µV
  • Residual THD+N (20 kHz BW)
    –105 dB + 1.4 µV
    Typically <–108 dB (1 kHz, 2.5 V)
    Typically <–110 dB (1 kHz, 2.5 V – option AG52 installed)
  • Individual Harmonic Analyzer
  • Max FFT Length
    1248K points
  • DC Voltage Measurement

APx52x B Series Full Specifications


  • 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.


  • Sine Frequency Range
    0.1 Hz to 80.1 kHz
  • Frequency Accuracy
    3 ppm
  • IMD Test Signals
  • Maximum Amplitude (balanced)
    21.21 Vrms
  • Amplitude Accuracy
    ±0.03 dB
  • Flatness (20 Hz–20 kHz)
    ±0.008 dB
  • Residual THD+N (20 kHz BW)
    –105 dB + 1.4 µV
    Typically <–108 dB (1 kHz, 2.5 V)
    Typically <–110 dB (1 kHz, 2.5 V – option AG52 installed)
  • Analog Output Configurations
    Unbalanced & balanced
  • Digital Output Sampling Rate
    27 kS/s to 200 kS/s
    27 kS/s to 108 kS/s Optical
  • Dolby / dts Generator
    Yes (encoded file)


  • Microsoft Windows 10 (64-bit) operating system.
  • USB 2.0 or USB 3.0 (two are required for optional switcher or DCX-127 use)
  • Intel i5 or better processor running at a clock speed of at least 2.5 GHz (AMD processors with similar specifications are also supported)
  • At least 8 GB RAM. 16 GB is highly recommended.
  • Internet connection or an USB Type A port (to access APx500 software for installation).
  • At least 1.5 GB of free hard disk space (an SSD for the operating system drive is recommended)
  • A color monitor and video card with at least SXGA (1280 X 1024) video graphics support (video resolution of 1900 x 1080 or greater is recommended)
  • More detailed information is available on our AP Software and Windows Compatibility chart