New Audio Digitization Performance Testing Guidelines and Software from FADGI

The following is a guest post by Kate Murray, organizer of the FADGI Audio-Visual Working Group and Digital Projects Coordinator at the Library of Congress.

The Federal Agencies Digital Guidelines Initiative is pleased to announce the release of ADCTest, an open source software application designed to facilitate performance testing of analog-to-digital converters (ADC) used in audio digitization preservation workflows. Developed by AVP in collaboration with Christian Landone, ADCTest automates a series of tests to measure the performance of ADC devices against FADGI’s 2017 Audio Analog-to-Digital Converter Performance Specification and Test Method Guideline (Low Cost).

Federal Agencies Digital Guidelines Initiative logo

Federal Agencies Digital Guidelines Initiative

A complement to the high quality ADC performance test guidelines approved in summer 2016, the pass-fail specifications recommended in the low cost guideline are for modified performance testing which takes into account minimum levels of performance, with lower equipment costs and requiring more modest engineering skills.  This low cost test guideline, approved by FADGI in September 2017, is not intended for absolute, high precision testing for the purpose of comparing the performance multiple ADCs, or analyzing nuanced aspects of ADC performance. Instead, its primary purpose is to provide users with a low-cost and simple test tool that will be employed routinely. In FADGI’s ADC performance testing work, we found that one of the biggest issues was that performance testing wasn’t being performed routinely, or at all, due to cost and complexity. Routine performance testing, even with lower performance test tools, enables the identification of significant failures, the relative comparison of ADCs in certain cases, and the ability to establish a benchmark for a given ADC to track trends in performance over time.

For more background and history of FADGI’s ADC performance testing project, see Avoid Jitter! Measuring the Performance of Audio Analog-to-Digital Converters.

The ADCTest software, available for download on the Library of Congress GitHub site, automates the testing protocol for all the low cost guidelines with a goal towards answering three basic questions:

  • Is my ADC/system failing?
  • How does my calibrated, healthy ADC perform relative to the guideline and other ADCs?
  • Is my ADC/system performing optimally relative to its own specifications?

It provides a flexible approach – with the ability to enable and disable individual test and accommodate support up to 24 bit, 96kHz signals – combined with easy to interpret pass/fail results, allowing users to customize the tool based on their needs.

Screenshot of ADC Performance Test tool interface for selecting test procedure

Selecting and deselecting tests to run in ADCTest.

ADCTest evaluates the performance of the ADC device against the seven criteria specified in the FADGI low cost guidelines including frequency response, dynamic range and crosstalk. The reports for each test are clearly identified as pass/fail against the FADGI criteria spelled out in the low cost guidelines.

Screenshot of ADC Perfomance Test tool interface

Pass/fail test results.

Double clicking on a given test will open up a detailed view of the test results to allow further investigation and interpretation. Users can even create their own test suite XML file and open it from the file menu to replace the FADGI test suite represented by default.xml in the application directory.

Screenshot of ADC Performance Test Tool options

Inserting a user-defined test suite.

ADCTest will continue to be refined with support from AVP and feedback is welcome through GitHub or directly to FADGI.

In keeping with FADGI’s goal to provide wide access to improved tools and workflows, ADCTest carries a BSD-3 license and the low cost guidelines carry a CC0 1.0 Universal license for worldwide use and reuse.

For more information about the FADGI ADC Performance Testing project, see http://www.digitizationguidelines.gov/guidelines/digitize-audioperf.html.

ADCTest software is available for download on the Library of Congress GitHub site.

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