APPENDIX 1

Suggested Road Map for Best Practices Document for Analog-to-Digital Conversion

January 30, 2004

George Massenburg

George Massenburg, a recording engineer and producer, and AES representative to the NRPB, presented this document to the participants on the second day of their meeting. Its purpose was to facilitate conversation about analog-to-digital conversion. The document sparked lively debate about such issues as the preferred sampling rate (e.g., for reformatting of audiocassettes) and evaluation criteria. Participants subsequently recommended that a separate meeting be focused solely on the topic of conversion. Mr. Massenburg’s document is produced here as a record of the meeting.

Objective: To capture complex analog signals with as much transparency to the original as practical.

1. Converter hardware criteria

1.1 Technical evaluation issues

1.1.1 Bit depth
Recommend: 24 bit

1.1.2 Sample rate
Recommend: 96 kHz or better

1.1.3 Linearity

1.1.4 Stability of clock reference (perhaps external)
Recommend: 100ps or better RMS jitter

1.1.5 Type and quality of anti-aliasing filter (mandate optimizing brick wall filter to track sample rate)

1.1.6 Noise

1.1.7 Dither (word-length reduction) methodology (if applicable for 16-bit archives)

1.2 Perceptive evaluation issues and protocols

1.2.1 Establish testing protocols

1.2.2 Establish source reference materials

1.2.3 Isolate evaluation criteria

2. Processing

2.1 Baseline procedures

2.1.1 Standardize subjective evaluation criteria

2.1.2 Develop conversion objectives

Observe that the costs of storage technologies are constantly shifting; determine possible interchangeability issues with other archives.

2.1.3 Establish evaluator group constituency

2.1.4 Establish consistency criteria across evaluators/technicians

2.1.5 Establish technical specifications (e.g., dynamic range, noise, flatness) for equipment and specifications for monitoring, including monitor speakers and room acoustics

2.1.6 Establish criteria (suggested is a “transfer confidence index”) to determine whether and when original materials must be retained for future reconversion

2.2 Archival processing-transfer

2.2.1 Specify conversion parameters within latitude of conversion options, if scaling of methodologies is determined to be acceptable
Examples: Recommend limiting single-channel conversion and single-channel files for purely monophonic sources (requiring more expert evaluation); recommend a deprecated bandwidth and resolution for limited-quality originals (for instance, old 78s and cylinders)

2.2.2 Determine the “transfer confidence” index
To what degree do I think that this conversion represents the best (i.e., maximally transparent, to a described, agreed-upon standard)?

2.2.3 Determine whether the specific original physical archive element is so deteriorated that improvements in conversion would provide little or no further advantage to existing archive materials

2.2.4 Establish whether and when original materials can be disposed of with confidence

2.3 Ongoing review

2.3.1 Calibrate and do technical reevaluation of equipment

2.3.2 Review and oversee methodologies; track technology

2.3.3 Correlate the database’s “transfer confidence” index with possible improvements in technology