Rebecca Chandler is a Senior Consultant at AVP. She specializes in collection care and management in support of preservation, planning, and advocacy. Rebecca is an experienced audio engineer, having worked in post-production at Broadway Video, Creative Group, and Sony Music Studios. Rebecca teaches and presents throughout the United States on the topics of audiovisual preservation, collection management, and digitization.
As we gear up to release a new version of ADCTest in the coming weeks, it occurs to me that we never formally introduced ADCTest in the first place. (And by “formally,” I mean in a completely informal blog post.) That’s something I aim to fix here.
What is an ADC? An analog-to-digital converter is arguably one of the most important components in the audio digitization workflow. This device takes an analog audio signal from, say, an audiocassette, and converts it to the bits a computer can read, store, and analyze.
How well should an ADC be expected to perform? How much do you want to spend? The folks over at FADGI recognized that realistically there are tiers of performance one can expect from an ADC and they created two guidelines around those tiers:
And for those of us without $20k to drop on test equipment: Audio Analog-to-Digital Converter Performance Specification and Test Method: Low Cost
Why should I test my ADC? There are at least three benefits to performance testing that the FADGI AV Working Group discovered in its work:
Benefit 1. You will be able to answer the questions: Did it pass? How did your ADC perform against the guideline recommendations?
Benefit 2. It forces you to crosscheck system setup. Equipment and systems may have been incorrectly installed and operators may not be fully attentive. The formality of running the test spotlights problems and motivates corrective action.
Benefit 3. It allows you to monitor your ADC’s performance over time. Running a test and retaining a report provides a benchmark: run the test again a few weeks later and compare. If something has changed, this finding will motivate further checking and correction if needed.
What’s great is that these benefits will apply to you whether you are using the High Level or Low Cost performance metrics.
Where does ADCTest come into play? So maybe you don’t have the $20k to spend on test equipment, nor the audio engineering chops to run it, but you want to be reasonably sure your ADC is performing optimally for its quality tier, your system is set up properly, and you want to track your ADC’s performance over time? Then ADCTest may work for you!
ADCTest is an open source software application designed to allow users with no audio engineering skills to automate the testing protocol for all criteria listed in FADGI’s Low Cost guidelines.
ADCTest was developed by AVP in collaboration with the developer Christian Landone, with great input and support by Kate Murray of the Library of Congress. ADCTest is not meant to replace the $20k test equipment referenced above, but rather to provide users with a low-cost and simple test tool that can be employed routinely. Routine performance testing, even with lower performance test tools, allows folks to be better able to recognize significant failures and establish benchmarks for their own ADCs, so as to track their performance over time.
Archives are frequently tasked with doing the best we can with what we have. ADCTest allows us to help ensure the quality of the audio assets we digitize, something that is becoming more and more important as our magnetic media continues to deteriorate and become obsolete.
1 While it generally is true that "you pay for what you get," our testing has shown that this is not always the case. We have found expensive ADCs to perform quite poorly in some areas and some more cost effective converters to perform quite well in some areas. Another good argument for testing!
2 The metrics and methods for measurement in the high level performance guideline offer the best possible confirmation of performance. Although the low-cost guideline and method does not confirm that an ADC is performing at the highest level, this testing regimen provides partial confirmation and will also identify serious shortfalls in performance.