APx555B Series Audio Analyzer

The New Standard - performance and versatility in audio analysis

APx555B Series High-Performance, Modular Two-Channel Audio Analyzer

The APx555 is a two-channel audio analyzer without compromise. Developed for R&D engineers and production technicians who need the highest possible performance, a broad range of digital I/O options and fast, intuitive software, the APx555 is the  standard for audio analyzers.



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.

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.

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.

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).

Made to Measure for Power Amp Designers

Measure continuous maximum output and peak maximum output automatically with Dynamic Intermodulation distortion (DIM) measurements. View power spectrum graphs with a regulated frequency sweep and take other measurements as specified by the CEA-2006 and CEA-490A standards. In addition to conventional balanced common mode rejection measurements, APx555 also enables CMRR measurements in accordance with IEC60268 section 14.15.1. Watch a Multi-Input Demonstration

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

Unprecedented Performance

With a typical residual THD+N of -120 dB and over 1 MHz bandwidth, the APx555 surpasses the analog performance of all other audio analyzers, including a 5 dB improvement compared to our legacy 2700 Series analyzer. Add to this FFTs of 1.2 million points and full 24-bit resolution, and you have performance unmatched by any other instrument.

Maximum Versatility in I/O

APx555 has two balanced and two unbalanced analog inputs and outputs plus 216k digital inputs and outputs via AES/EBU, TOSLINK and SPDIF. Additionally, I/O may be expanded with optional Digital Serial, HDMI with ARC, PDM and Bluetooth modules. A new Advanced Master Clock (AMC) module handles input and output clock signals to synchronize the APx555 with external equipment (or vice versa), and the AMC also enables jitter generation and analysis. AMC comes standard with the APx555.



Advanced Digital I/O (standard)
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.

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 and 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 APx 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 APx555. 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.

ADC Test Mode (SW-555ADCTEST)
For design engineers validating and testing complex, multichannel analog-to-digital converters (ADCs), the APx555 B Series now offers an ADC Test Mode option capable of generating balanced analog audio signals mixed with a calibrated common mode DC offset voltage. This optional feature is especially useful in testing devices that operate on a single supply voltage and require inputs with a DC bias voltage, such as audio codecs and ADC chips in mobile products. The ADC Test Mode also includes programmable voltage limits to prevent overvoltage damage to the device being tested.

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.



  • Sine Frequency Range
    0.001 Hz to 80 kHz, DAC
    5 Hz to 204 kHz, Analog
  • Frequency Accuracy
    3 ppm, DAC
    30 ppm, Analog (Precision Tune)
  • IMD Test Signals
  • Maximum Amplitude (balanced)
    26.66 Vrms
  • Amplitude Accuracy
    ±0.03 dB
  • Flatness (5 Hz–20 kHz)
    ±0.008 dB
  • Residual THD+N (22 kHz BW)
    –117 dB + 1.0 µV
    Typically <–120 dB (1 kHz, 2.0 V)
  • Analog Output Configurations
    unbalanced, balanced (differential & single-ended), CMTST
  • Digital Output Sampling Rate
    27 kS/s to 200 kS/s
    27 kS/s to 108 kS/s Optical
  • ADC Test VBias Range
    –0.4 to +4.2 VDC


  • 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.


  • Maximum Rated Input Voltage
    230 Vpk
  • Maximum Bandwidth
    >1 MHz
  • IMD Measurement Capability
  • Amplitude Accuracy (1 kHz)
    ±0.03 dB
  • Amplitude Flatness (10 Hz–20 kHz)
    ±0.008 dB
  • Residual Input Noise (22 kHz BW)
    =1.0 µV
  • Residual THD+N (22 kHz BW)
    –117 dB + 1.0 µV
    Typically <–120 dB (1 kHz, 2.0 V)
  • Individual Harmonic Analyzer
  • Max FFT Length
    1248K points
  • DC Voltage Measurement

APx555 B Series Full Specifications


  • 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