I can never decide if I’m elated or appalled by digital audio and its potential. It’s empowering and disempowering in equal measure. It’s not entirely clear yet how historians can use it.

Digital audio grows from the insights of Claude Shannon: that everything can be reduced to information. Music or audio can be reduced to frequencies mapped to a grid in time. There is almost no limit to what you can do with a digital audio file.

Audio in your computer can take two forms. It can be audio waveforms–for example, someone plays a saxophone, or speaks into a microphone, and you press record. The sound is recorded as a set of frequencies mapped in time. You can perform various operations on those files–change pitch, speed up, slow down, cut up and paste.

Image of an Audio File


The example above is an audio recording of a bass guitar, which you can hear if you click the image. You can see each individual note as it is plucked and then decays. A recording of your voice would look very similar.

Or sound in your computer can take the form of “MIDI” (Musical Instrument Digital Interface) information.

MIDI (musical instrument digital interface) information is basically three things: pitch, velocity, and duration. So you press a key on the piano. Midi encodes which note you struck, how hard you struck it, and how long the note rang. In the image below, the color of the bars represents velocity, the length of the bars represents duration, and the position of the bars top to bottom represents pitch, as shown in the piano keyboard on the left margin. If you have an electronic keyboard at home, and it has a USB port, it is capable of outputting midi.  Once you have midi information, you can assign it to any other instrument sound, using “samples.”

Image of a Midi File


Imagine we have a piano, and some microphones, and a piano player. She comes in and we ask her to play every note on the piano, at, say, 6 velocities, and for 6 durations. We record each one of those–well over 1000 individual sound files–and then we have a “library” of piano “samples.” We do the same for a sax and a flute and a violin and a church organ. We can then map the midi information to one of those libraries. So the same midi information can “trigger” different sampled instruments: a sax, a piano, a drum set.

Below is a midi file, ‘triggering” various samples. It’s the same file as in the image above. It was played on a small plastic keyboard which makes no sound on its own, it simply outputs midi information. It was then mapped to samples of a piano, a Hammond organ, a string section, a choir, and a guitar. It could have been mapped to any instrument or sound you can imagine.

Midi samples

And here is that file in its original context

Original file in context

In that file, the horns are samples triggered from a keyboard, the organ is a sample, and the drums are precorded loops. Fun! But what can I do with this?

To work with Digital audio, you want a DAW, a “Digital Audio Workstation.” There are a lot of them available for various prices.

Audacity–a free, open source DAW with extensive functions but a less than charming interface, and clumsy for working with MIDI. If all you want to do is edit files, do basic recording, and change files from one format to another, Audacity is a fine choice. It does not come with many “loops” or samples.

A great deal of the creative power of a DAW comes with the use of re-recorded loops or sample libraries. As you will see on Tuesday, “loops’ allow anyone to make a song, and “sample libraries” allow you to make the sound of virtually any instrument. Below are some options that make it easier for non-musicians to create music.

On Mac OS

  • GarageBand–free to Apples users, easy and fun with surprisingly deep functionality. Comes with a wide range of free samples and “loops”–see demo session Tuesday.
  • Logic Pro–Apple’s professional audio software. It’s a steal at $200. It comes with @ 10 gigabytes of sample sounds and a huge library of loops

On a Windows machine

  • Reaper–an inexpensive ($69) fully featured DAW that comes with a free sixty day trial. It does not come with many pre-recorded loops or sample libraries.
  • Pro Tools–the industry standard, ridiculously expensive
  • Mixcraft–it’s similar to Garageband in how it uses loops; and in having a simple, easy interface. It’s priced around $50-100. There is a reasonably full-featured 14 day free demo.

To record your own audio, for music or, say, for an audio narration or a podcast, you should probably get a microphone. The simplest way to do this is with a USB microphone, which has a preamp and a chipset for converting analog audio to digital information. You just plug in the microphone and start recording.

For class, if you are on a Mac make sure you have Garageband installed and the “additional content” downloaded. If you are on a Windows machine download the free trial of Mixcraft



Intro to working with Digital Audio

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