Contents

Chapter 1
Foundations

1.1 Features (and limitations)

• Most common audio formats are supported (some of them directly such as Ogg Vorbis, WAV (Windows wave), FLAC (Free Lossless Audio Codec) or AIFF (Macinthosh Audio Interchange File Format) ... and others such as MP3 (by means of LAME) or AAC (by means of FFMPEG)).
• Sample precission can be 16, 24 or 32 bits/sample. Therefore, it cannot capture 8 bits/sample and therefore, use logarithmic quantization. However, it can export these formats throught libsndfile.
• Several audio effects.
• Expandable using plug-ins from LADSPA (Linux Audio Developer’s Simple Plugin Api) and writting plug-ins using the Nyquist programming language.
• Several analysis tools.
• It is cross-platform and free (GPL)!

1.2 Terminology

• Project: A collection of tracks, clips, labels, amplitude envelope points, gain and pan data.
• Track: A sequence of audio samples.
• Clip: A pieze of a track.
• Label: A name for a collection of samples of a track.
• Amplitude envelope point: A way to control the amplitude of a track along time.
• Gain: A measure of how much a signal is amplified. 0 dB means not amplification nor attenuation.
• Pan: Controls the spread of a stereo sound into the stereo channel.
• Sync-Locked Track Groups: lets you keep existing audio or labels synchronized with each other even when carrying out actions like inserting, deleting or changing speed or tempo.
• Stereo track: a 2-channel track where each channel is a independent audio signal.
• Mono track: a 2-channel track where there is only one audio signal (the same for each channel).
• Left/Right track: a 1-channel track with data for, only, the left/right channel.
• Label track: Used to reference points or regions in the project’s audio tracks.
• Time track: It is used in conjunction with one or more audio tracks to progressively increase or decrease playback speed (and pitch) over the length of the audio project (only one Time traks per project is allowed).
• Playback Region: a track region associated with a shaded selection region in the waveform which is indicated in the timeline by a thin horizontal gray bar with arrowheads on each end.
• Overdubbing: is the process of record sound while the existing tracks are played.
• Speed: The number of samples/second played.
• Tempo: It refeers to the playing time but not changing the pitch.
• Pitch: The fundamental (first one) frequency of a sound (usually, a music note).

Chapter 2
Synthesis (Generate Menu)

2.1 Tones

1. It is possible to generate pure tones (Generate->Tone):
   1. Sine: A mathematical sine function.
   2. Square: A pure periodic squared window function. Notice that this “tone” is physically impossible.
   3. Square (no alias): Similar to the Square wave but does not produce aliasing distortion.
   4. Sawtooth: Has a gradual upwards slope followed by a shorter downwards slope.
2. And time-decaying tones (Generate -> Chirp). Using this option you can define a change in the frequency and the amplitude.

2.2 Dual-Tone Multi-Frequency (DTMF) tones

• Generate -> DTMF Tones.
• For each tone you wish to generate, enter numbers from 0 to 9, lower case letters from a to z, and the * and # characters. You can also enter the four “priority” tones used by the US Military (upper case A, B, C and D). Use the slider to select the ratio between the length of each tone in the series and the length of the silences between them.

2.3 Noise

• Generate -> Noise.
• Generates white, pink and brownian noise during a period of time. Notice that these noises have a different frequency composition.

2.4 Silence

• Generate -> Silence.
• Generates an ausence of signal during aperiod or time.

2.5 Clicks train

• Generate -> Click Track.
• Generates a sequence of regular pulses at the selected tempo.

2.6 Pluck

• Generate -> Pluck.
• Generates a synthesized pluck tone with abrupt or gradual fade-out, and selectable pitch corresponding to a MIDI note.

2.7 Risset Drum

• Generate -> Risset Drum.
• Produces a sound based on work by the composer of electronic music, Jean Claude Risset.

Chapter 3
Recording and playing

3.1 Sound driver selection

• By default, in Linux, Audacity will use ALSA which is the best choice for avoiding latency issues during capturing audio.

3.2 Input (recording) and output (playing) selection

• Depending on your audio hardware, a number of input devices are available. Again, in Linux systems, ALSA native “hw” devices should minimize latency problems.

3.3 The Transport Toolbar

• The Transport Toolbar is the easiest way to control Audacity playback and recording. From left to right we found:
  1. The Pause Button: press once to pause playback or recording then once to resume.
  2. The Play Button: press once to start playback from the beggining.
  3. The Stop Button: interrupts the playing/recording.
  4. The Skip to Start Button: moves the time cursor to the start of the project.
  5. The Skip to End Button: moves the time cursor to the end of the project.
  6. The Record Button: start a new audio capture (you must push Stop to stop this process).

3.4 Using keyboard shorcuts

1. P: Pause.
2. SPACE: Plays or stop.
3. SHIFT+SPACE: Plays in a loop.
4. HOME: Skip to Start.
5. END: Skip to End.
6. R: Record.
7. SHIFT+R or SHIFT+Record: Append-Record. Record starting from the end of the selected (previously existing) track(s).
8. SHIFT+A: Stop and set cursor. When stop a playback or a recording, the cursor or start of the selection is set to the position where playback/recording was stopped.

3.5 Measuring your latency

• Latency is an issue that depends mainly on your hardware (sound device and computer) and your audio buffer size (Edit -> Preferences -> Recording -> Audio to buffer).
• In order to minimize the latency, you can improve your hardware and/or reduce the audio buffer size. However, reducing the audio buffer size can produce underruns in the capturing process if the CPU is not able to manage this configuration requirement.
• When overdubbing (see Section 3.9), you must measure and set your current lantency in Edit -> Preferences -> Recording -> Latency Correction, otherwise those audio tracks that have been previously captured will be the synchronized with the new ones.
• To find out your latency you must capture a sound produced by your computer and compute the delay between the time the sound has been produced and the time the sound has been captured. To do this:
  1. In Selection Toolbar make sure that "Snap To" is set to "Off".
  2. Above the second group of numbers, make sure that “Length” is selected.
  3. Click on one of the downward-pointing arrows in the digits boxes to the right of “Snap To” and select “hh:mm:ss + milliseconds”.
  4. Generate 2 bars of click track (Generate -> Click Track), and choose the default “Ping” sound.
  5. Click “OK” to generate the click track.
  6. Now click the Record Button in the Transport Toolbar.
  7. You will get a new track. The top track is the original click track, the bottom track is the looped-back recording.
  8. Zoom in so you can see one of the clicks in the top track and its delayed version on the bottom track.
  9. You can now read the latency directly from the second panel of numbers.
  10. Write in the Edit -> Preferences -> Recording tab -> Latency Correction Entry the negative of this number.
  11. Repeat this experiment to check if the latency when overdubbing has been “hidden”.

3.6 Timer recording

• The Transport -> Timer Record Dialog allows to configure a temporized recording (starting date and time and duration).

3.7 Playing slower/faster

• Use the Transcription Toolbar to change the playing speed.

3.8 Time warping

• Progressively increase or decrease playback speed (and pitch).

3.9 Overdubbing

• By default, Audacity record and plays tracks simultaneously. See Transport -> Overdub (on/off).

Chapter 4
Analysis (Analyze Menu)

4.1 Contrast

• Analyze -> Contrast.
• Can be used to compare the audio level of two different parts of a mono track. Suppossing that one of the parts is the foreground (that obviously also has a background noise) and the other is the backgroud (with only background noise), this analysis can be useful to know if there is enoung signal (20 dB or more) in the foreground section compared to the background section.
• Procedure:
  1. Select a region containing the signal (speech, for example). This is the "foreground" selection.
  2. Click the “Foreground”’s “Measure selection” Button.
  3. Select a region containing only the background sound. This is the background selection.
  4. Click the “Background”’s “Measure selection” Button.

4.2 Clipping ocurrency

• Analyze -> Find Clipping.
• Displays runs of clipped samples in a Label Track.
• You can control the length of the clipped runs (default 3 samples) and the number of unclipped samples (default also 3) that must occur before a sun of clipped samples will be determined.

4.3 Frequency analysis

• Analyze -> Plot spectrum.
• Graphs the spectral density function of the sound.
• You can choose between:
  1. Spectral analysis: A genuine Fourier analysis.
  2. Autocorrelation: A measure of the redundancy of the signal.
  3. Cepstrum: The power cepstrum $C$ (of a signal) is the squared magnitude of the Fourier transform of the logarithm of the squared magnitude of the Fourier transform of a signal. Mathematically:

     $$C=\left|{\mathcal{ℱ}}^{-1}\left({log}_2\left(|\mathcal{ℱ}{|}^2\right)\right)\right){|}^2$$

     Physically, the cepstum resents the rate of change in the different spectrum bands. It’s particularly useful for properties of vocal tracks and is used, for example, to identify speakers by their voice characteristics.

4.4 Localize beats

• Analyze -> Beat Finder.
• Place labels at beats which are much louder than the surrounding audio.

4.5 Track splitting

• Analyze -> Regular Interval Labels.
• Places point labels in a label track so as to divide the associated audio into smaller, equally-sized segments.

4.6 Silence finder

• Analyze -> Silence Finder.
• Divides up a track by placing point labels inside areas of silence.

4.7 Sound finder

• Analyze -> Sound Finder.
• Divides up a track by placing region labels for areas of sound that are separated by silence.

Chapter 5
Editing (Edit View and Tracks Menus)

5.1 Creating a new tracks

• Mono track: go to Tracks -> Add new -> Audio Track.
• Stereo track: go to Tracks -> Add new -> Stereo Track.
• Label track: go to Tracks -> Add new -> Label Track.

5.2 Splitting and joining tracks

• Using the Track Drop-Down menu you can:
  1. Split a stereo track into separate tracks for left and right channels after choosing Track Drop-Down -> Split Stereo Track.
  2. Split a stereo track into two separate mono tracks after selecting Track Drop-Down -> Stereo to Mono.
  3. Swap the channels in a stereo track.
  4. Join two mono, left or right tracks into one stereo track, by selecting Track Drop-Down -> Make Stereo Track..

5.3 Mixing tracks

• When you reproduce (push the Play Button) a project, all tracks are mixed together in order to play them, but you don’t have a track that can be written into a stereo audio file with the result of our project.
• The Mix and Render Option of the Tracks Menu explicitly mixes down all selected tracks to a single mono or stereo track. The resulting track (called “Mix”) replaces the selected tracks and is placed underneath any tracks that were not mixed and rendered.
• It is possible also to mix and render to a new track by using CTRL+SHIFT+M.

5.4 Zooming the time scale

• To zoom in, position the mouse pointer over a track and left-click. To zoom out, shift-click or click the right mouse button.

5.5 Zooming the amplitude scale

• Hover the mouse over the vertical ruler of a track, and the pointer changes to a magnifying glass, indicating you can zoom vertically.

5.6 Resampling

• Resampling is usually used to match a given audio format (such as the CD quality audio).
• However, resampling increments the number of samples (and therefore the amount of memory) but not increases the quality of the sound.

5.6.1 Project resampling

• Tracks -> Resample ... and select the new sampling rate.

5.6.2 Track resampling

• Audio Track Pop-up -> Set Rate ... and select the new sampling rate.

5.7 Repeat

• Effect -> Repeat.
• Repeats the selection the specified number of times.

Chapter 6
Built-in Amplitude effects (Effects Menu)

6.1 Scaling (amplification/atenuation)

• Effect -> Amplify -> Amplification (dB).
• Similar to move the potentiometer of your amplifier.
• In a stereo track, the balance between the left and right channels will be preserved.

6.2 Normalization

• Effect -> Normalize -> Normalize maximum amplitude to.
• Similar to scaling, but removes the DC offset.
• In a stereo track, the balance between the left and right channels can be preserved (uncheck Normalize stereo channel independetly).

6.3 Fadding

• Effect -> Fade In | Fade Out | Adjustable Fade.
• Produces smooth starts and finishes in the audio tracks.

6.4 Temporal amplitude attenuation (duck)

• Effect -> Duck.
• Reduces (ducks) the volume of one or more selected tracks whenever the volume of a specified "control track" reaches a particular threshold level.

6.5 Compression

• Effect -> Compressor.
• Reduces the dynamic range of audio, ampliying the quiet sounds.

6.6 Hard Limiter

• Effect -> Hard Limiter.
• Such as the Compression Effect, although clipping can happen.

6.7 Leveler

• Effect -> Leveler.
• A simple, combined compressor and limiter effect for reducing the dynamic range of audio. It reduces the difference between loud and soft, making the audio easier to hear in noisy environments or on small loudspeakers.

6.8 SC4

• Effect -> SC4.
• Another stereo compressor.

6.9 Bass and Treble

• Effect -> Bass and Treble.
• Increases or decreases the lower frequencies and higher frequencies of your audio independently.

6.10 Change Pitch

• Effect -> Change Pitch.
• Change the pitch of a track without changing its tempo (speed).

6.11 Equalization

• Effect -> Equalization.
• Allows you to increase the volume of some frequencies and reduce others.

6.12 High Pass Filter

• Effect -> High Pass Filter.
• Removes frequencies above the cutoff frequency.

6.13 Low Pass Filter

• Effect -> Low Pass Filter.
• Removes frequencies below the cutoff frequency.

6.14 Paulstretch

• Effect -> Paulstretch.
• Slow down audio without changing the pitch.

6.15 Phaser

• Effect -> Phaser.
• Displaces frequencies of the audio and the displacement is controlled by a low frequency sine signal.

6.16 Tremolo

• Effect -> Tremolo.
• Is the variation of the amplitude of the sound controlled by a sine signal (amplitude modulation).

6.17 Vocoder

• Effect -> Vocoder.
• Modulates the left channel of a stereo track with the right channel and viceversa.

6.18 Wahwah

• Effect -> Wahwah.
• Uses a moving (back and forth in the frequency) bandpass filter to create its sound controlled by a low frequency oscillator.

6.19 Declicking

• Effect -> Click Removal.
• Remove clicks (especially suited for those procuced by vinyl records) without damaging the rest of the audio.

6.20 Reconstruct clipped regions

• Effect -> Clip Fix.
• Reconstruct clipped regions by interpolating the lost signal.

6.21 Noise Removal

• Effect -> Noise Removal.
• Reduce constant background sounds such as “hum” (zumbido), “whistle” (silvido), “whine” (gemido) or “buzz” (rumor), and moderate amounts of “hiss” (siseo).

6.22 Notch Filter

• Effect -> Notch Filter.
• Sharply attenuates frequency-specific noise like mains hum or electrical whistle with minimal damage to the remaining audio.

6.23 Repair

• Effect -> Repair.
• Removes a very short region (up to 128 samples) of damaged or destroyed audio, replacing it with an estimated region of audio based on what is happening either side of the region.

6.24 Truncate Silence

• Effect -> Truncate Silence.
• Reduces the length of passages where the volume is below a specified level.

6.25 Change Tempo

• Effect -> Change Tempo.
• Change the tempo of the selection without changing its pitch.

6.26 Change Speed

• Effect -> Change Speed.
• Change the speed of a track, affecting its tempo, pitch and frequency content.

6.27 Sliding Time Scale / Pitch Shift

• Effect -> Sliding Time Scale / verb|Pitch Shift|.
• Make a continuous change to the tempo and/or pitch of a selection by choosing initial and/or final change values.

6.28 Delay

• Effect -> Delay.
• A multiple echo effect.

6.29 Echo

• Effect -> Echo.
• Repeats the audio you have selected again and again, normally softer each time.

6.30 Reverb

• Effect -> Reverb.
• Adds reverberation (rapid, modified repetitions blended with the original sound that gives an impression of ambience).

6.31 Invert

• Effect -> Invert.
• Flips the audio samples upside-down, reversing their polarity. Notice that if you play the original and the inverted audio together, both tracks will be substracted.

6.32 Reverse

• Effect -> Reverse.
• Reverses the selected audio.

6.33 Nyquist Prompt

• Effect -> Nyquist Prompt.
• Write your own plug-ins created using the Nyquist programming language.