Audio Precision System compatible USB adapter

The older Audio Precision System instruments are very capable audio analyzers, especially for analog work. However they are missing modern PC connectivity and the control software does not run on modern Windows systems.

This APIB (Audio Precision Interface Bus) compatible USB adapter provides a simple and cost effective way to use your older AP System One, System Two, System Two Cascade, or ATS-2 on modern Microsoft Windows systems.

The AP control software and Visual BASIC scripts runs flawlessly – without a virtual machine or emulator – on modern Windows systems.

The USB adapter works by replacing the dynamic link library for low level bus communication.

The new library redirects the low level bus communication to the standard Microsoft WinUSB driver, which is built-in on newer Windows systems.


The Audio Precision compatible USB adapter is tested with APWIN 2.24 (Build 1390) and ATS_1.5.
Older versions of the control software may work too, but are not tested. Newer APWIN version do not work.

Any Audio Precision hardware that is supported by APWIN 2.24 or ATS 1.5 will function with the adapter:

Supported Windows systems:

Ordering information

The price of the adapter is 290 € excluding shipping.

Please send email with your shipping address to if you want to order, or if you need information.

Software Installation

  1. Install the Audio Precision APWIN 2.24 control software, if it is not already installed, using an Administrator account. Adjust User Account Control (UAC) to the lowest level, install and return to the previous level. Some Anti-virus programs may prevent Installshield from finishing the installation on newer Windows systems. If the installation hangs, reboot Windows in Safe Mode and restart the APWIN software setup. Installing different AP software packages (like ATS-2 and APWIN) can cause trouble because of shared environment variables. Typically the Icons for the measurement scripts (like "Analog Frequency Response") do not work as the PATH is incorrect. If you see blurred fonts try the program compatibility options. Right click on APWIN.EXE and click on "Properties". Set the "Overwrite high DPI scaling behavior" to "Application" (Do not set the "Run this program in compatibility mode" option).
  2. Download the new low level bus communication DLL apio.dll from Overwrite the original apio.dll in the APWIN installation directory with the apio.dll from the zip file. The apio.dll is typically installed in "C:\Program Files\Audio Precision\Apwin200" or "C:\Program Files (x86)\Audio Precision\Apwin200".
  3. Install the Microsoft WinUSB driver

    If you are using Microsoft Windows 8 or newer, the Microsoft WinUSB driver is already preinstalled and you are done.

    For Windows 7, Windows Vista and Windows XP, download the USB driver installation utility from For manual USB driver installation, the USB driver files can be downloaded from Extract and start the USB driver installation utility. A wizard will guide you through the USB driver installation. Click the pictures below for step-by-step instructions.

    • Driver installation guide for Windows Vista/7

    • Driver installation guide for Windows XP

  4. Connect the USB adapter to your AP System and to your PC and switch it on. AWPIN detects your AP System as usual.

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Discontinued Audio Precision Models
A survey of the discontinued Audio Precison models on the site. Unfortunatly a lot of information and downloads have beed discarded with the new webpage layout.
APWIN 2.24 download link
The latest Audio Precision control software, which supports the older System One and Two models.
ATS_1.5 download link.
The ATS-2 control software version 1.5, which supports ATS-2.
USB adapter thread on
A rather long thread with lot of details about the USB adapter on the diyAudio site. Many bugs in the software were fixed with the help of diyAudio members.
LinkedIn, Classic AP Audio Systems Group LA
The Classic AP Audio Systems Group LA on LinkedIn with helpful and experienced users. This has replace the older LinkedIn, Classic AP Audio Systems Group