Digital preservation for any type of file includes many components, such as: Choosing a sustainable digital format. Choosing a sustainable storage media. Identifying recordings that you want to preserve. Organising materials, including tagging, embedding metadata into files, and placing files in structured directories. Naming the directories with dates and events make them easier to identify in the future. Refreshing the data at regular intervals and storing multiple copies (three is recommended) on different media types, and in different geographical locations if possible. Keeping a copy in the cloud can be part of that strategy, but do not rely solely on the cloud as the only storage solution. Migrating the data from one file format to another as formats markedly improve and/ or evolve. Managing the data by utilising an asset management system that also allows you to easily export content.
Audio Guidance This section contains practical advice on preserving a variety of audio recordings.
Sampling Rate: The frequency at which information from the original recording is sampled or collected from a continuous signal. The rate is given in hertz (Hz) which equals cycles per second. One common example is the audio CD which has a sampling rate of 44,100 Hz, or 44.1 kHz.
Bit Depth: The number of data bits used for each individual sample. The amount of bits determines the number of discrete levels possible to place a sample within. 8-10 bit is common for video; 16-24 bit is common for audio.
Compression: Use of a method to reduce the size of digital files or streams of data, also referred to as data reduction. Compression is used to either save data storage space or better enable movement over networks or transmission lines. There are many different techniques to compress data, but all fall into one of two overall categories: Lossless: Any data removed can be reconstructed. Lossy: Some or all of the data removed is discarded and gone forever.
Audio preservation copies generally have the following characteristics: High sampling rate, High bitrate, No or very little compression, Open or non-proprietary formats,
Audio access copies generally have the following characteristics: Reduced sampling rate, Low bitrate, Fairly compressed Files, may be delivered on hard drive, flash drive or optical disk.
Video Guidance: Playback and Digitization of Materials
You should ask the vendor for a preservation copy to be stored for the long-term and for an access copy to make your content readily accessible. The purpose of a preservation copy is to create a high quality duplicate of the original record. This way, if the original record deteriorates beyond use the preservation copy will be able to take its place. A preservation copy should last for years or decades – at least long enough to plan for making subsequent copies once these become outdated.
The purpose of an access copy is to create a copy of your record that you can play back easily. For example, if you have a VHS tape that is difficult to play back, you can have a DVD or mp4 file created to allow you to play back that content on a computer or DVD player. An access copy should be a well-supported format that is easy to play back.
Video preservation copies generally have the following characteristics: High resolution High bitrate No or very little compression Open or non-proprietary formats Video access copies generally have the following characteristics: May be reduced resolutions
Low bitrate Fairly compressed Files may be delivered on hard drive, flash drive or optical disk; whichever method you select you should be prepared to make a second, or backup, copy to help ensure the safety of your records.
Resolution: The measure of how well audio, video, or film can faithfully portray images or sound. Picture cell (pixel) density and bit depth are the units of measure for individual images. Sampling rate and bit depth are the units of measure for moving images and sound.
Bit Rate: The amount of sample data that is collected per unit of time. This is usually expressed as ‘bits per second’ (bps) or ‘Megabits per second’ (Mbps), and is the result of sampling rate multiplied by the number of data bits per sample (or bit depth), plus any additional data such as tracking information.
Compression: Use of a method to reduce the size of digital files or streams of data, also referred to as data reduction. Compression is used to either save data storage space or better enable movement over networks or transmission lines. There are many different techniques to compress data, but all fall into one of two overall categories:
Lossless: Any data removed can be reconstructed. Lossy: Some or all of the data removed is discarded and gone forever.
Whichever method you select you should be prepared to make a second, or backup, copy to help ensure the safety of your records.
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