4.2 Types of Audio Files

Introduction

An apparatus that uses binary code such as a computer or an iPhone manages sound in a digital format. There are many different types of playback devices and various  ways these files are stored.  Additionally, analog sound systems are still used to play and archive sound. An audio engineer can quickly discover there exists a vast expanse of recording formats that are not easily compatible or accessible. Understanding how the older systems work can help with most modern versions. And vice-versa. Take time to play and listen to music on a wide range of equipment from different eras. Learn how to convert one to the other and your expertise in the production field will certainly grow.

People that work in audio production need to know the differences between varying digital and analog files, how to convert one to another, and what each is best used for (technical). How we save our files, and how we transmit these files, and why we do so could be considered the method in our three pillar approach. The order in which we present these audio files or perhaps the final decision on where to share these files would fall under our creative approach.

For example, in the past, I’ve been hired to convert a client’s old 78 vinyl record collection  into  digital files that could be played and organized on a typical home laptop computer. That required choosing the right equipment and cables to play records at the right speed and turning that analog signal into a digital one. Once transferred to my computer, I could then make some equalization adjustments and bring the overall volume up  (or down) to a presentable level. Finally, I had to convert those large files into smaller MP3 files that I could electronically send back to the client.

In addition to the audio, I scanned the liner notes and artwork and included those attachments along with with MP3s. Once again, I used my technical knowledge to identify what equipment would be needed, I used different methods and orders of operation to make quality conversions, and I topped it off with some creative approach in packaging the final product so that it was an artistically unique experience for my client.

Digital Audio File Formats

There are two major groups of audio file formats:

• Those using lossless compression, e.g. like WAV, FLAC
• Those using lossy compression, e.g. MP3, Ogg Vorbis, WMA, AAC

In the lossless compression of a piece of data, nothing is lost during the compression and the original data is restored upon uncompressing. In lossy compression, some data is lost during compression and upon uncompressing the data is not identical to the original but possibly close to it. Lossy compression is used mainly in the compression of multimedia data like audio or video where the loss of some details is tolerable under certain conditions, e.g., the human eye is unable to discern the loss in certain details of an image or video.

Audio Guidance: Identifying Audio Formats

How Do I Identify Audio Formats?

Sound recordings come in a variety of shapes and sizes and have been around since the late nineteenth century. While there are a number of audio formats you may find at home or in a professional environment, each one presents different requirements for identification, physical handling, and playback equipment used. Some of the more common types of audio include ¼-inch open reel tape, audio cassettes, and grooved disc recordings.

Magnetic Media

Open Reel Quarter Inch Tape

Magnetic recording tape was invented in 1928. However, it wasn’t until the late-1940s that the recording industry fully adopted the format. Compared to grooved recordings, magnetic tape offered higher fidelity, longer record times, and the ability to be edited.

¼-inch open reel audio tape is supplied in reels having a diameter of 5-inches, 7-inches, and 10.5-inches and may vary in length depending on the tape speed. 1-inch and 2-inch open reel tapes (in width) also exist and were primarily used in professional environments.

• There are different types of tape base for ¼-inch width audio tape. Acetate and polyester are most common, although you may encounter PVC or paper base as well.
• An easy way to tell if you have one of the two most common types of ¼-inch tape is to hold the tape up to a light source. If the tape appears opaque it is polyester; if the tape is translucent, it is acetate.
• Tape speeds vary between 30 ips (inches per second) to 15/16 ips, with speeds of 7.5 ips and 3.75 ips being the most common.

Audio Cassette

This tape format was introduced in the United States in the mid-1960s by Phillips. Cassette recordings have been used for a number of purposes, including oral histories, lectures, conferences, and music. Since they were primarily used for convenience and not necessarily quality, cassettes are not considered to be a stable or high fidelity medium.

• Cassettes are made with polyester base tape, have just over a 1/8th inch tape width, and a slow playback speed of 1 7/8 ips, thus contributing to a limited dynamic range and frequency response.

Wire Recording

An alternate form of magnetic recording, the wire recording was initially introduced in the late 19th century, but further developed in the US during WWII. Spools are about 3 ½-inches in diameter. This format was ultimately succeeded by tape due to its low sound quality. While stainless steel wire recordings (post WWII) are not susceptible to the same types of degradation as open-reel tapes, they may be damaged easily and playback equipment is obsolete. You may find the wire recordings in your collection date from around the 1940s-1960s.

Magnabelts

These magnetic belts are similar in appearance to dictabelts and were used for dictation purposes, but do not contain grooves.

Digital Audio Tape (DAT)

Digital Audio Tapes were introduced by Sony in 1987, and are magnetic tapes that store audio digitally. A cartridge houses a 4mm magnetic tape and recordings can be at, below, or above the 44.1 kHz sampling rate of CDs.

Grooved Recordings

You may encounter grooved discs at home or in professional collections. Discs vary in size and speed and have different coatings and substrates, which may include:aluminum, lacquer/acetate, plastic, and cardboard. Below are several of the more common types of phonograph records:

Wax Cylinders

The earliest recording medium produced commercially, these are grooved wax- cylinders, which are the predecessors to the grooved disc. Wax cylinders can be solid or have a core of cardboard. They are very fragile and should be handled with care, including the grooves which can easily be scratched.

Attribution & References

Except where otherwise noted, this page is adapted from “Unit Two, Part Three: Types of Audio Files” In Audio Production Course Manual by Mark J. Lindquist, CC BY-NC-SA 4.0

• Audio file formats is adapted from: FOSS Open Standards/Comparison of File Formats , CC BY-SA
• How do I identify audio formats Courtesy of National Archives and Records Administration, PDM