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Sound recordings

This page provides specifications for sound recordings, including minimum standards and best practice for digitising and born digital recordings.

Specifications Sound recordings: Archival master files 

Minimum standard

Digitising analogue recordings

The minimum standard for digitising sound is 44,100 samples per second (44.1kHz), 16 bits per sample (16-bit) to WAV or AIFF format. This is the standard for CD audio, but a higher standard is recommended.

Born digital

For existing files:

  • Archive the original or source file
  • If the file format is not likely to be accessible over time (and even if it is), consider transcoding the file to WAV or AIFF format and cataloguing the metadata embedded in the originating file format
  • If the item is a recording on an audio CD, use an audio CD ripper to extract (‘rip’) tracks to WAV or AIFF. On Windows, CDex is a simple, free utility

When recording audio:

  • Record at 44,100 samples per second (44.1kHz), 16 bits per sample (16-bit) to WAV or AIFF format
  • If the recording device doesn’t allow for recording to WAV or AIFF, use the highest quality setting. If an MP3 recorder, record at 320 kilobits per second (typically shown as 320 kbps) with a Constant Bit Rate (CBR) and a sample rate of 44.1kHz

Best practice

Digitising analogue recordings

  • Digitise sound at minimum 48kHz (preferably 96kHz), 24 bits per sample (24-bit) to WAV or AIFF format
  • Use a dedicated analogue to digital converter, available on a professional, external soundcard (also called an audio interface) that connects to a computer via FireWire or USB

Born digital

For existing files:

  • Archive the original or source file
  • Transcode the file to WAV or AIFF format (48kHz or 96KHz, 24-bit) and catalogue the metadata embedded in the originating file format
  • If the item is a recording on an audio CD, use an audio CD ripper to extract (‘rip’) tracks to WAV or AIFF. On Windows, CDex is a simple, free utility

When recording audio:

  • Record audio at minimum 48kHz (preferably 96kHz), 24 bits per sample (24-bit) to WAV or AIFF format.
  • If the recording device doesn’t allow for recording to WAV or AIFF, use the highest quality setting. If an MP3 recorder, record at 320 kilobits per second (typically shown as 320 kbps) with a Constant Bit Rate (CBR) and a sample rate of 44.1kHz.

Rationale

WAVE (short for Waveform Audio File Format. The file extension is ".wav") and AIFF (Audio Interchange File Format) are widely used audio file formats. As uncompressed audio file format types, they are suitable for archival purposes as they maintain the most accurate digital representation of a sound file. The wide use of WAVE is another major reason to use that format; as stated in the  IASA publication Guidelines on the Production and Preservation of Digital Audio Objects :

The wider the acceptance and use of the format in a professional audio environment, the greater the likelihood of long term acceptance of the format, and the greater the probability of professional tools being developed to migrate the format to future file formats when that becomes necessary.

If working on Windows or Linux operating systems, WAVE is most convenient; on Mac OS and Unix operating systems, AIFF.

Note that WAVE format is limited to files that are less than 4GB. This is equivalent to about 6.8 hours of CD-quality audio (44.1 kHz, 16-bit stereo). An alternative in this instance would be the Broadcast Wave Format (BWF). BWF is same as WAV but its value is that it can incorporate metadata into the headers which are part of the file.

‘Lossy’ file formats like MP3 use algorithms to simplify audio content and reduce file size. This process results in some of the audio information being irretrievably lost. MP3 is not an appropriate format for digitising analogue recordings. However the format’s popularity and widespread use means that it is likely that born digital MP3 audio recordings - perhaps music recordings or podcasts - will meet a collection’s selection criteria. In this instance, note that MP3 audio files maintain significant metadata that should be recorded if the file is transcoded to WAV or AIFF. ID3 is a metadata container that allows information to be stored in the file itself. ID3 on Wikipedia

 ‘Lossy’ audio file formats are widely used on the web. Not only is file size optimised, but web browsers now play many of these file formats without requiring plugins. For the definitive overview, see Mark Pilgrim’s Dive Into HTML5. A working knowledge of these file formats will help guide decisions on collection development, archiving and access.

For more, see Creating digital audio by DigitalNZ.