Survey of Audio Digitization

Introduction

I'm J, and this is the page of audio information I've gathered for the Spring '06 Survey of Digitization (SoD) class at the School of Information at UT-Austin. I am not an expert, but a musician, music collector, and audio enthusiast. This site will focus, for the sake of the SoD students, on questions surrounding the digitization of audio at libraries, collections, and archives. This site is for those who may be involved in some way with the care of audio and its migration from analog to digital.

For the first of my two, three hour classes I've decided to concentrate on covering all the concepts and issues involved in working with analog/digital (a/d) conversion. The second class can then focus on the dilemmas involved with actual projects, particularly our own final project: the digitization of cassettes from the Benson Library at UT-Austin.

Overview of Sound and Recording

• Sound Basics
• Brief History of Recording
• Analog Formats
• A/D Conversion and Digital Formats

Sound Collections and Guides

• The Library of Congress
• The Macaulay Library of Natural Sounds
• More Metadata!
• Best Practices Guides
• Resources of Resources

Our Digitization Project

• Assignment
• Quality Control

A few basic points of my own:

° More than with the ears we hear with the mind.

° The audio preservationist and restorationist needs to understand/hear every stage of a sound's life-cycle. (Ideally, this requires knowledge of genres and traditions, ethnography and musicology, vocalization and instrumentation, score and arrangement, players, acoustics, analog recording technology, formats and playback technologies, sound engineering, digital technologies, etc.)

° Though audio archives need preservation standards and fixed playback options, formats and players constantly evolve in a race to their own extinction.

Andrew Dylan's points from his commencement of the Sound Savings Symposium on why sound matters:

° Sound is a medium that is intimately tied to tests of copyright limits in our society. And this is most blatantly so since sound is a medium in high demand by consumers.

° Music and sound are transcultural in a manner that is not so for text. Whether white men can play the blues may never be resolved in some purists' minds, but there is no doubting that the representations of history and culture that are captured in music can be processed and enjoyed by people outside that culture. The rise of world music, the merging of cultural styles, and the worldwide love of opera by people who cannot speak a word of Italian are testimony to the emotional response people have to music.

° The next tidal wave of digital content is rich media, a seamless convergence of audio, video, and text. As yet, true hypermedia of the kind envisaged decades ago has yet to emerge and even the Web, in all its glory, is (with some noticeable exceptions) a text-heavy medium. Audio is the great underutilized resource. Hypermedia in popular use is a visual medium, with audio seen as ‘extra’, but there are signs that this will change.

Sound Basics

What is sound? "Sound can be defined as the change in air pressure above and below an equilibrium (usually the barometric pressure). For example, when a bass drum is struck, the skin vibrates back and forth. As the skin travels outwards, away from the center of the drum, the air pressure surrounding the drum rises above the barometric pressure; conversely as the drum skin travels inwards, the air pressure lowers. This to-and-fro action occurs numerous times per second creating waves of compression and decompression in surrounding air. As air pressure increases by the outward motion of the bass drum skin, the eardrum is pushed towards the center of the head; conversely, as pressure decreases, the eardrum travels away from the center of the head. The higher the vibration speed, the higher the pitch; the larger the change in air pressure, the louder the sound." By Gilles St-Laurent, Music Division, National Library Of Canada, from here.

There is a good animated gif of a sound wave's low/high pressure oscillation against a membrane here.

Check out this old black and white short, "How the Ear Functions."

Sound Perception

Human's generally perceive sound in the pitch range between 20Hz to 20,000kHz. "For those that are curious, the lowest note on the piano is A sounding at 27.500 hz and the highest is the top C sounding at 4186.009 hz (cycles per second). A440 concert pitch refers to tuning the A above middle C to 440.000 hz." from here.

Humans generally perceive sound in the noise intensity range as quiet/low as about 4dBA. On the upper end, noise generally becomes painful around 120dBA. Hearing loss is a function of noise level over time. Maximum exposure should be limited to about 85dBA for 8hrs. 110dBA can damage your ear after a minute and a half, 140dBA can cause damage in an instant, and perforation of the ear drum could occur around 160dBA.

Here is a scale to give you an idea of decibel levels:

10 normal breathing
20 whispering at 5 feet
30 soft whisper
50 rainfall
60 normal conversation
70 TV audio
85 handsaw
110 shouting in ear
120 thunder

For a more exhaustive list of common sounds and their decibel levels go here.

Can You Trust Your Ears?

Equal-loudness contour: this graph represents the change in loudness necessary across the audible pitch range for the pitches to be perceived at equal loudness.

Effect of Loudness Changes on Perceived Pitch - A high pitch (>2kHz) will be perceived to be getting higher if its loudness is increased, whereas a low pitch (<2kHz) will be perceived to be going lower with increased loudness. -from here.

Psycho-acoustics (from Wikipedia):It is important to note that the question of what humans hear is not only a physiological question of features of the ear but very much also a psychological issue.

Say this: Maresy-doats and dozy-doats, and liddle lamzy divey. A kiddley divey too, wouldn't you-oo? The way you hear it depends on whether you know what you're saying, which greatly affects interpretation. It's about animals eating oats. How do you hear it now? Sound is its own language. The more you know about what you're listening to, the more you hear. Recording, listening, making sound, dubbing recordings, making conversions, are all a psycho-acoustical art and science.

Brief History of Recording

Sound Timelines

• Vintage Audio History by Video Interchange (a transfer and conversion service)
• A Wikipedia Timeline of audio format developments
• The History of Sound Recording Technology's Overview of Technologies for Recorded Music
• Recording Technology History by Steve Schoenherr
• The Audio Engineering Society Timeline of Significant Events

A Few Major Events in Early Audio Technology

1876 Telephone - Alexander Graham Bell patents his telephone, built with the assistance of young self-trained engineer Thomas A. Watson. Elisha Gray, who developed a similar device at about the same time, will unsuccessfully

1877 Phonograph - Working with a team of engineers at his Menlo Park, New Jersey, laboratories, Thomas Alva Edison perfects a system of sound recording and transmission. The first recording replayed is a voice saying "Mary had a little lamb its fleece was white as snow." from here.

1916 Microphone - E.C. Wente at Bell Labs developed the condenser microphone to translate soundwaves into electrical waves that could be transmitted by the vacuum tube amplifier.

1918 Speaker - Henry Egerton at Bell Labs patented on Jan. 8 the first balanced-armature loudspeaker driver.

1921 P.A. System - The amplifier, microphone, loudspeaker innovations were combined at Bell Labs to create the first public address systems.

1928 - Nyquist presented his theorem stating that an analog signal should be sampled at regular intervals of time and twice the frequency of the signal's bandwidth to reproduce it with good fidelity.

1931 Hi-Fi Recording - in April, Leopold Stokowski invited Bell Labs to begin sound recording experiments with his Philadelphia Orchestra. In December, the first electrical recordings were made and continued throughout the 1931-32 concert season. 125 of these test recordings have been preserved (a limited edition album of these masters was released in 1980 by Bell Labs).

1932 Stereophonic Recordings - in March, several test recordings were made at the Academy of Music using two microphones connected to two styli cutting two tracks on the same wax disk. This recording is the earliest example of stereophonic recording that has survived.

1957 A/D Conversion - "New forms of playback, file formats, compression and storage of data are all changing on a seemingly daily basis, but the underlying mechanisms for converting real-world sound into digital values, manipulating those data and finally converting them back into real-world sound has not varied much since Max Mathews developed MUSIC I in 1957 at Bell Labs...The importance of their work to information theory, computing, networks and digital audio cannot be understated. For example, the same data stream theory used in high-speed networking, known as T-1 lines is the same technology used in higher-end Digidesign Pro Tools systems today (TDM or time division multiplexing). A widely used method for encoding and decoding binary data, such as that used in digital audio, pulse code modulation or PCM was also developed early on at Bell Labs, attributed to John R. Pierce..." Jeffrey Hass

Analog Formats

We've read "How to Care for your Audio," from the National Film and Sound Archive about basic care for your audio. Let's take a look at a few formats you might find in the basement. Most info gathered from here.

• Material - Originally they were a blend of plant and animal waxes that was a bit too variable. Then Brown wax cylinders were made of metallic soap composite. Then came Gold-Molded, Amberol, Celluloid and others.
• Handling - Handle by inserting middle and index fingers in the center hole, then gently spread them to just keep the cylinder from slipping off. Do not touch the grooves of wax cylinders; they are very susceptible to mold. Wax cylinders should be at room temperature before touching; the thermal shock from the warmth of your hand can cause cold wax cylinders to split.

Disks - Many types of disks have been produced over the last 100 years. Here are a two common ones.

Acetate

• Material - Continuous Shrinkage of the lacquer coating due to the loss of the castor oil plasticizer is the primary destructive force. The gradual loss of plasticizer causes progressive embrittlement and the irreversible loss of sound information. Because the coating is bonded to a core which cannot shrink, internal stresses result, which in turn cause cracking and peeling of the coating.

Vynil

Vynil Bowls - make your own!

• Material - Thus far, vinyl has proven to be the most stable of the materials that have been used in the manufacture of sound recordings.

All Disks

• Storage - Use soft polyethylene inner sleeves. Do not use paper or cardboard inner sleeves and do not store records without inner sleeves.
• Handling - Handle all grooved discs (78s, 45s, LPs, and acetate discs) by their edge and label areas only.

Magnetic Tape - Magnetic tape first appeared in North America just after World War II.

• Material - Magnetic tape is made up of two layers: a "base" layer, and a thin "binder" layer which is bonded onto the base. The binder contains ferromagnetic particles whose permanent alignment within the binder produce the copy of sound waves. It is prone to sticky-shed syndrome: The most common and serious magnetic tape degradation occurs through hydrolysis, the chemical reaction wherein an ester such as the binder resin "consumes" water drawn from humidity in the air to liberate carboxylic acid and alcohol. Hydrolysis in magnetic tape results in the binder shedding a gummy and tacky material which causes tape layers to stick together and inhibits playback when it is deposited onto the tape recorder heads. The added friction increases tape stress and can cause machines to stop. Hydrolysis also causes a weakening in the bond holding the binder to the backing, which results in shedding or possible detachment.
• Storage - After being played, not rewound.
• Handling - Handle by the outer edge of the reel flanges and center hub areas only. Do not squeeze flanges together -- it will damage tape edge.
• Playback - many reel-to-reel players still exist, though there are a diversity of formats, and they too are usually in need of repair, cleaning, and calibration.

General Handling and Storage Rules

• Store in a facility that stays within a constant cool temperature and low humidity, and has very limited exposure to u/v light.
• The air conditioning system should be equipped with dust filtering equipment.
• Store most formats standing up, not laying on down on their sides.
• Never touch the surface of a recording. Use clean, white lintless cotton gloves and handle by the edges.
• Recordings should not, unnecessarily, be left exposed to open air. Return items to their containers when not in use and never leave storage containers open.
• Do not place recordings near sources of dust including paper or cardboard dust. Keep the surrounding area clean.
• Do not consume food or beverages in the area in which recordings are handled.Keep storage facilities as clean and dust-free as possible.
• Keep labeling to a minimum, but limit the placement of labels, especially pressure sensitive labels, to the container using conservation ink.
• Keep equipment clean, well adjusted and in good working condition.

Good Resources

• Library of Congress
• Library and Archives of Canada

Analog/Digital Conversion and Digital Formats

I found these sites to be good at explaining the process:

• A Digital Audio Primer from The MP3 Handbook
• Introduction to Computer Music: Volume One, Chapter Five: Digital Audio
• How Analog and Digital Recording Works at How Stuff Works
• Analog Vs. Digital from audioMIDI.com Classroom

Digital Formats

• Guide to Sound Recording Media - Sarah Stauderman (Smithsonian Archives)
• Digital Audio Formats from The MP3 Handbook
• ID3 Tags for More Metadata with MP3s
• Understanding Digital Audio Formats from informit.com

Library of Congress

The Save Our Sounds Project - Dr. Michael Taft (Library of Congress), Head, Archive of Folk Culture, American Folklife Center

Factors considered in choosing which sounds to save for the Save Our Sounds project:

° Content.
° Historical or cultural significance.
° Present state of accessibility.
° Fragility and deterioration.
° Variety of sound recording formats.
° Complexity of collections.
° Diversity of material.
° Other political considerations.

Review of Audio Collection Preservation Trends and Challenges - Sam Brylawski (Library of Congress), Head, Recorded Sound Section Motion Picture, Broadcasting and Recorded Sound Division

"The Library's collections include over 100,000 audio cassettes and 170,000 open-reel tapes."

"Indeed, there is no permanent digital format."

"Following the Open Archival Information System (OAIS) model established by NASA,6 digital objects for sound recordings in the repository will include digital images of record labels or tape boxes and other graphics or accompanying text, in addition to the audio files. The audio files themselves will be very large, recorded at a sampling rates of 96kHz or 192 kHz, with 24-bit word lengths."

LOC uses Metadata Encoding and Transmission Standard (METS):

"METS is complicated. Because it requires populating a very large number of fields, at the present, it is time-consuming to create a full METS record. Officials at the Library of Congress hope and expect to "develop tools for automatically creating metadata," as recommended in a study of challenges related to the preservation of digital content."

The Macaulay Library of Natural Sounds at Cornell University

Info gleaned from this article at RLG DigiNews.

• 160,000 recordings of bird, insect, frog, and mammal vocalizations
• Analog formats included acetate disk, cassette, and open reel-- in various stages of deterioration
• Started with 3, moved to 6 studios

Audio control issues

• Playback equipment calibration
  • visually inspected for excessive wear patterns
  • adjust tape tension; set low speed to provide gentle handling of fragile tapes
  • calibrate reel-to-reel to known international standards using calibration tapes from Magnetic Reference Laboratories, Inc: head alignment (height, wrap, and azimuth), playback equalization, playback reference levels, absolute speed, and wow and flutter.
  • biweekly calibration/alignment using a computer-based test set manufactured by Audio Precision; stored and routinely compared for performance over time; easy to spot problems before they have a negative effect on the transfer process
• A/D Converter and Editing System
  • reviewed A/D converters, narrowed to six possibilities, requested in-house testing units and audition; though all six had very similar published specifications, the actual sound character or lack thereof was very different.
  • After grueling A/B listening tests and spectral analysis, final decision: the Prism Dream AD-2, the only device that did not color (alter) our signals...were indistinguishable from our highest-quality analog sources.
  • A/D conversion requires ultra-clean power supplies; exceptional grounding procedures; ultra-stable clocking devices; high-quality, low-tolerance components; and exceptional printed circuit board design
  • Chose for 48-bit data path throughout system; most workstations are 32 bit
• Digital Media
  • pre-determined: optical-disc rather than tape based; storage requirements were going to be huge, 32MB/minute of 2-channel audio; 96kHz sampling rate, 24-bit
  • options available at the time: CD-R, DVD-RAM, and DVD-R
    • CD-R: good player compatibility, excellent life expectancy, and low cost but fell short in terms of capacity
    • DVD-RAM offered increased capacity and long life expectancy but was expensive and did not offer the archival security of a write-once format
    • DVD-R offered everything we require
• Digital Format - goal: as generic a digital collection as possible, maximizing accessibility and migration to the next generation of digital storage
  • wanted DVD-Audio but soon realized that industry-imposed copy-protection schemes would significantly hamper our accessibility and future migration requirements
  • chose DVD-ROM using the Universal Disc Format (UDF) standard
  • Audio Interchange File Format (AIFF) data files
  • audio file has a voice ID at the beginning with the asset number, which in our case is the MLNS catalog number
  • same number is also used as the digital file name
  • No other metadata is embedded in the audio file. Due to the common occurrences of species splitting and renaming we chose to store all relevant metadata in a separate relational database.
• Disk Writing
  • written using Pioneer DVR-S201 using DVD-R 4.7GB Authoring version 2.0 media
  • uses a 635nm-laser wavelength instead of the general-use 650nm-laser; still fully compatible with all DVD readers
  • designed for authoring and replica masters, higher quality, more consistent than the general-use discs
  • Maxell, TDK, and Pioneer in lots of 100 to 200 at a time to minimize any batch-related problems
  • custom DVD authoring program from Sonic Solutions handles the actual disc formatting, writer control, and bit/bit verification
  • 60 minutes/4.3GB of data.
  • in-house testing has revealed that the disc quality decreases near the extreme outer diameter of the disc, so we limit our data to 4.3 to 4.4GB/disc
  • two, first-generation discs containing roughly 125 min. stereo/250 min. mono; One disc is placed in a large Plasmon D-480 robotic jukebox for in-house distribution, while the second is stored off site at a secure, climate-controlled, underground storage facility
• Quality control - many years of experience testing CD-R technologies
  • issues: writer/disc compatibility, writing-speed issues, and dye-formulation problems; differences often manifest themselves as significantly higher-than-acceptable error rates or tracking problems
  • DVD-R technologies appear to share some of these same issues so every disc created undergoes a series of rigorous tests
    • Using an AudioDev Computer Aided Test System (CATS), we first test every blank disc. During this test phase the disc is subjected to 20 different tests that measure such values as disc reflectivity, push-pull, wobble signal-to-noise, land pre-pit level, block error rate (BLER), etc
    • testing blank disks saves time and money writing (w/expensive lasers) to bad disks
    • lastly, test quality of the writing process using the CATS: Over 50 important parameters are tested during this phase, including servo and tracking, jitter analysis, digital errors, dropouts, HF parameters, and physical measurements. The results of this process offer a pass/fail report
    • quality control reports stored electronically
• Accessibility/Distribution
  • DVD-R discs our high-resolution “core-archive,” available only in-house via a high-speed network
  • external distribution via the Internet includes a CD-Audio quality 44.1kHz/16-bit wave file, a 96kbp/s MP3 file, a multi-bitrate RealAudio streaming file, and soon, a QuickTime streaming file

  Future Proofing
  Only time will tell, but if history is any indication, we assume that in the not-too-distant future some new and better digital format for long-term preservation will appear in the market place. Unfortunately, as technology changes, it typically renders existing hardware and software obsolete. In the meantime we will monitor new digital storage technologies while continuing to grow what we believe to be a very robust and accessible digital storage solution. When an improved, standardized digital format does appear, we feel confident that we have set the stage to migrate data from our current storage strategy to the next generation in a relatively painless and automated fashion.

More Metadata!: iTunes v. Preservation

When metadata is lost in the transfer from analog to digital, we lose more than we realize. This article makes the point that, "Online music stores should facilitate rather than hinder access to this information before, during and after a song or album is purchased."

• The Digital Music Era - downloading music from a free P2P network are aware that, in terms of the absent and incorrect information that comes with MP3s, they get what they pay for
• Release Dates - "released" often refers to the date the CD version of an album was released
• Albums - the continuous release of compilations can make it difficult to identify original albums
• Partial Albums - The store should list the complete songs in order, with the unavailable songs shaded out.
• Identity Crisis - Removing the identity of artists is one of digital music's largest threats to jazz preservation
• Album Notes - Most jazz albums for sale in the ITMS have none of the original album's liner notes or session information. When "Album notes" is included info and quality is extremely variable
• Get Info - should include in "Get Info" not make listener log back in to view "Album notes" on site
• Album Design - Album covers shrank drastically when CDs were introduced. They vanished in P2P interfaces. They have returned as thumbnails in the ITMS. With the loss of so much other info, browsing by album art may be the most effective way for jazz fans to find music.
• Act Now - Email your favorite digital music store: Suggested text: I am a loyal customer who would buy more music from your store if it was sold with the same information (cover art, photos, dates, liner notes, session and songwriting credits) that I get when I purchase a CD.

Best Practice Guides

• Creating Digital Audio Resources: AHDS Guide to Good Practice
• Digital Audio Working Group: Digital Audio Best Practices
• NINCH Guide to Good Practice in the Digital Representation and Management of Cultural Heritage Materials
• University of Arkansas Libraries: Audio Digitization Guidelines
• Capturing Analog Sound for Digital Preservation: Report of a Roundtable Discussion of Best Practices for Transferring Analog Discs and Tapes
• LOC Audio-Visual Prototyping Project
• Emeld School of Best Practices: Digitization of Audio Files
• Guidelines for Outsourcing (.doc)
• Questions to Ask Before Beginning a Digital Audio Project (.doc)

Resources of Resources

These are sites with lots of great links to information about audio archiving.

• Sound Savings: Preserving Audio Collections
• Audio Preservation and Restoration from U of Washington Music Library
• Audio Preservation edited by Hannah Frost at Stanford
• Audio Archiving Resources

Audio Assignment

Thanks to Uri, we have a box full of cassettes from the Benson Library in need of digitization. Each of you will get a cassette to digitize and a spreadsheet to fill in for your audio project. The purpose of this assignment is to give you some experience with audio digitization and to help the Benson out. This is not a difficult project; I will lead you through it step-by-step and hopefully, we will produce digital copies of these tapes just as though we were the digitization lab hired to do the job.

Assignment: Digitize both sides of the tape assigned to you, filling out all the metadata fields given to you on the spreadsheet for documentation and quality control. Produce the raw capture .wav files, archival access .wav copies, and network/internet access .mp3 files for each side of the cassette. Burn a CD of the archival access copies with a track for each side.

Deliverables:

• 2 archival masters, raw, un-edited 24bit/96kHz wave files - one for each side of the tape.
• 2 archival access copies - 24bit/96kHz wave files with the major silences edited out- one for each side of the tape.
• 2 variable bit rate .mp3 files of the edited archival access copies- one for each side of the tape.
• 1 .xls spreadsheet, which I will give you, filled in as completely as possible.
• 1 CD containing 2 tracks, side a and side b, with a printed label

Where to deliver them:

The audio files will go in our project folder on the network, 2007-spring\projects\ischool-blac-aud-... Inside this folder, create a folder with your UTEID for its name, in lowercase. Inside your folder, create three folders:

• an "archival master" folder for the 24bit/96kHz archival master,
• a "publication master" folder for the 24bit/96kHz archival publication master
• an "access derivative" folder for the VBR mp3 archival access derivative
• a "CD" folder for each side of tape, saved at 16bit/44.1kHz, and a 16bit/44.1kHz 2 track CD containing sides a and b

Gradable Components

• 2 pts. for having completed the archival master transfer, named it correctly, and named your folder correctly
• 2 pts. for having completed the archival publication master transfer, named it correctly, and named your folder correctly
• 2 pts. for having completed the archival access derivative transfer, named it correctly, and named your folder correctly
• 2 pts. for having filled in the metadata spreadsheet completely and performed the quality control measures
• 2 pt. for producing the CD containing 2 tracks, side a and side b, with a printed label

Quality Control

You will be performing three quality control measures and reporting them on the spreadsheet:

1. Are there strange noises? - I would like you to randomly select 10% of your audio to listen to for noises that may have entered the audio file during digitization. These are things that might occur because of a malfunction in the A/D converter, the processor, power, etc. Note: using the computer you are doing the digitization on for anything else while digitizing could cause such noise. Don't have any other application running while digitizing. A momentary lapse in processor resources could mar your audio. Since we are digitizing 90 minutes, 10% comes out to about 10 minutes to listen back to. Select any 5 minutes from each track to listen for anything "digital sounding" that doesn't sound like it came from the tape. Once you have listened to 5 minutes of each, and are satisfied there are no strange digital noises, circle the "no" under "strange noises," and move on. If you do hear something funny, circle"yes" and make note of where it occurs and what it sounds like.



2. Does the digital dub sound the same as the original? This is a listening test I would like you to perform on the first ten seconds and the last ten second of each side. I've chosen such a small amount of time so that you can effectively listen to the tape and then listen to the digital with the sound of the tape in mind. You will need to unplug the headphones from the Audiophile box and plug them into the tape player directly, going back and forth to compare. Do it a few times. Do they sound the same? If yes, circle"yes" under "sound the same?" If no, try to describe what the difference is in the notes. I'd like you to do this at the beginning and end to confirm that nothing dramatic changed during the process that you might not have been aware of, but which colored the audio somehow.



3. Was there any clipping? Clipping occurs especially easily in digital recording when the signal is too loud to be processed resulting in distortion. It can be detected visibly when the audio signal fills the audio wave window so much that it hits the ceiling/floor and is simply flat. Visually scroll through the capture audio for signs of clipping. If you see any, listen to it to see if it distorts, causing unwanted noise. If you find any, circle "yes" under "any clipping" and note where is occurs and how bad it interrupts the audio track. If you don't see any, circle"no." In the following picture clipping is occurring to the red and orange waves, not the blue ones:



4. If you answered "yes" to "strange noise?", "no" to "sounds the same", or "yes" to "any clipping," circle "yes" under "needs redub," and explain how serious you thing the problem interrupts the audio, or if perhaps it only need redubing if we are going to be perfectionists about the audio.