Adobe Software - Video and Audio

Apply effects efficiently with scripting and batch processing

Excerpted from �Adobe Audition 1.5 Classroom in a Book� by Adobe Systems Incorporated.

Working with digital audio often involves working with multiple files of similar nature. Applying an effect to a single file does not take very much time, while applying the same effect to 50 individual files is a time-consuming process. Scripting in Adobe� Audition� allows you to apply effects to many files in a few easy steps.

In this tutorial, you�ll first create a script and run it on individual files. Later, you�ll learn how to use the Batch Processor to run on the script on multiple files.

Create and run a script

Open a session (*.ses file) that contains several sound files.
Double-click on a sound file (*.cel) in order to open it in Edit View. Scripting can only occur in the Edit View.
Choose Options > Scripts. The Scripts window opens. We will be applying an effect to this window and using it as a template to apply to other sound files.
In the Scripts window, click the Open/New Collection button. A window opens asking you to Choose a new Script file or enter a new name. The default Scripts folder, which is a subfolder in the main Audition 1.5 folder, is displayed, revealing the default scripts that are included with Audition. If the Scripts folder is not displayed, navigate through your hard drive to the Scripts subfolder located within the Audition 1.5 folder.

Note: A Script collection may include either one script or a number of different scripts.
Enter myCIBscripts.scp in the File name field and click Open. This saves your new script collection into the default Scripts folder. A script collection file uses the file extension of .scp.
In the New Script section of the Scripts window, enter the name Bass Boost & Dynamic Delay in the Title field, and then press the Record button. When recording, any effects you apply to the waveform are monitored and saved, so they can be applied to other files in the future. The recording only keeps track of the options selected, not the time it takes to select the options.
Choose Effects > Delay Effects > Dynamic Delay. The Dynamic Delay window opens. Choose Spacey from the list of presets. Press the Preview button to hear the effect of the Dynamic Delay. Click OK when done previewing. Dynamic Delay changes the amount of delay over the length of a waveform.
Choose Effects > Filters > Graphic Equalizer. The Graphic Equalizer effect boosts or cuts specific frequency bands and provides a visual representation of the resulting EQ curve. In the bottom left corner of the Graphic Equalizer window, choose the Simple Bass Lift preset. This preset primarily boosts the lowest frequencies and is similar to turning up the bass on a stereo system. Click the Preview button to hear the bass lift. Click the bypass option to hear the difference between the two settings. Click OK after previewing the edited clip.
Choose Options > Scripts to reopen the Scripts window. Click the Stop Current Script button to stop recording. Keep the Scripts window open.

Note: Had you applied additional effects to the waveform, the Script would have continued to record the additional effects.
In the blank text field at the bottom of the window enter Added Dynamic Delay and boosted Bass as a reminder for the next time you use this script.
Click the Add to Collection button and the Bass Boost & Delay loads into the Script Collection window on the left side of the application window. Note the description field is now locked. Anyone using this script will now see this description. Additionally, this provides a helpful reminder of which effects are used and in what order they are applied.
Click the Close button. You will now run this script on another file.
In the Organizer window double-click another *.cel file to view its waveform. If you do not see other sound files in the Organizer window, you need to import some. Click the Import File button located in the Files tab, locate the sound files, and then shift-click several sound files to import them.
Choose Options > Scripts from the menu. Click on the Bass Boost & Dynamic Delay script and click the Run Script button. The two effects are applied automatically and a confirmation window appears when the script is complete. Click the OK button to close the window.
Press the spacebar on your keyboard to play the clip. The same effects added to the clip you opened in step 2 have automatically been added to this clip.
Double-click the first sound file you ran the script on. Choose File > Save As, click the New Folder button, and then create a file with the name Batch_Process_Output. In the Batch_Prcoess_Output folder, click the New Folder button again to create a folder named Tutorialfiles_Space. Name the file you are saving Testfile01_Space.cel and open the Tutorialfiles_Space folder, then click the Save button. By naming the file with a unique name, the original file is retained.
Double-click the file you opened in step 13 and choose File > Save As. Navigate to the Tutorialfiles_Space folder if needed. Name the file you are saving Testfile02_Space.cel and click the Save button.

Use the Batch Processor to apply your script to multiple files

Running scripts on individual files is a quick way to apply multiple effects to a single waveform. When you need to apply a script to more than two or three files at a time, it is more efficient to use Audition�s Batch Processing feature.

If necessary, switch to the Edit View by clicking on the Edit View tab. It is necessary to use the Edit View because Batch Processing is not available in the Multitrack View.
Choose File > Batch Processing and the Batch Processing window opens. Note at the bottom of the window there are 5 tabs; Files, Run Script, Resample, New Format, and Destination. These tabs represent the five steps you need to follow in order to successfully complete a Batch Process.
Click the Add Files button to open the Choose Source Files window. Navigate to the folder containing the sound files you want to run the script on. Shift-click to select the files you want to load into the Batch Processing window, and then click Add. Click the Hide Path option to see the short names of the files.
At the bottom of the Batch Processing window, click the second tab, Run Script. If necessary, select the Run a Script option. The first field points to a Script collection file. You created a script collection file named myCIBscripts.scp earlier in this tutorial. If you do not see this script collection file click the browse button and locate the Scripts folder in your Audition 1.5 folder.
Along the bottom of the window, click the Resample tab. In the Resample tab, confirm the Conversion Settings checkbox is not selected. The conversion settings would allow you to convert files with different sample rates, bit depth and number of channels into one consistent setting, however you will not be converting in this tutorial.
Click the New Format tab along the bottom of the window. Click on the Output Format drop-down menu to open it and choose Audition Loop (*.cel). Using this option you can convert all the files into a new format when using the Batch Processing command.
Click on the Destination tab along the bottom of the window. If necessary, select the Other Folder option and then click the Browse button. Navigate to the Batch_Process_Output folder. Click the plus sign and then click to select the TutorialFiles_Space folder. Click OK to confirm the destination.
In the Output Filename Template type *_Space.cel. When creating a template, pay attention to the placement of the asterisk, as the asterisk will append the corresponding section of the filename. For example, Filename01.cel will become Filename01_Space.cel, and Filename02.cel will become Filename02_Space.cel.
Click the Run Batch button. The Bass Boost & Dynamic Delay script is run and applied to all of the selected files. The files are exported to the specified folder, in the file format you selected. Audition displays a window to confirm it is done.
To open the modified files and confirm the changes, choose File > Open and select the TutorialFiles_Space folder. Shift-click to select the *.cel files in this folder, and then click Open to import the selected files into the Organizer window.
Double-click one of the sound files in the Organizer window and press the spacebar. As you listen to the file you should note the dynamic delay effect and the bass lift that was applied using the batch process.
Choose File > Close All to close the session and its media.

Understanding the fundamentals of sound is the first step in learning about digital audio. In this primer, we�ll introduce the basics of sound so you can work more effectively with Adobe� Audition� and the rest of your digital audio or video toolkit.

Sound fundamentals

Sound is created by vibrations, such as those produced by a guitar string, vocal cords, or a speaker cone. These vibrations move the air molecules near them, forcing molecules together, and as a result raising the air pressure slightly. The air molecules that are under pressure then push on the air molecules surrounding them, which push on the next set of air molecules, and so forth, causing a wave of high pressure to move through the air; as high pressure waves move through the air, they leave low pressure areas behind them. When these pressure lows and highs�or waves�reach us, they vibrate the receptors in our ears, and we hear the vibrations as sound.

When you see a visual waveform that represents audio, that waveform represents these pressure waves. The zero line in the waveform is the pressure of air at rest. When the line swings up, it represents higher pressure, and when it swings low, it represents lower pressure. This waveform is the equivalent of the pressure waves in the air.

A sound wave represented as a visual waveform: A. Zero line B. Low pressure area C. High pressure area

Waveforms

Amplitude reflects the change in pressure from the peak of the waveform to the trough. Cycle describes the amount of time it takes a waveform to go from one amplitude, all the way through its amplitude changes, until it reaches the same amplitude again. Frequency describes the number of cycles per second, where one Hertz (Hz) equals one cycle per second. That is, a waveform at 1,000 Hz goes through 1,000 cycles every second. Phase measures how far through a cycle a waveform is. There are 360 degrees in a single cycle; if you start measuring at the zero line, a cycle reaches 90 degrees at the peak, 180 degrees when it crosses the zero line, 270 degrees at the trough, and 360 degrees when it completes at zero. Wavelength is the distance, measured in units such as inches or centimeters, between two points with the same degree of phase.

A single cycle at left; a 20 Hz waveform at right: A. Wavelength B. Degree of phase C. Amplitude D. One second

When two or more sound waves meet, their amplitudes add to and subtract from each other. If the peaks and troughs of the two waveforms line up, they are said to be in phase. In this case, each peak adds to the peak in the other waveform, and each trough subtracts from the other troughs, resulting in a waveform that has higher amplitude than either individual waveform.

In-phase waves reinforce each other.

Sometimes the peaks of one waveform match up with the troughs of the other waveform. The peaks and the troughs will cancel each other out, resulting in no waveform at all. Such waveforms are said to be 180 degrees out of phase.

Out-of-phase waves cancel each other out.

In all other cases, the waves are out of phase by some other amount. This results in a waveform that is more complex than either of the original waveforms; continuing to add waves makes a more and more complicated waveform. Keep in mind, however, that a single instrument can create extremely complex waves on its own because of the unique structure of the instrument, which is why a violin and a trumpet sound different even when playing the same note. When you see music, voice, noise, or other complicated sound represented by a waveform, you are seeing the result of adding all of the waveforms from each sound together.

Two simple waves combine to create a complex wave.

Analog audio

A microphone works by converting the pressure waves of sound into changes in voltage on a wire. These changes in voltage match the pressure waves of the original sound: high pressure is represented by positive voltage, and low pressure is represented by negative voltage. Voltages travel down the microphone wire and can be recorded on to tape as changes in magnetic strength or on to vinyl records as changes in amplitude in the groove. A speaker works like a microphone in reverse, taking the voltage signals from a microphone or recording and vibrating to re-create the pressure wave.

Digital audio

Unlike analog storage media such as magnetic tape and vinyl records, computers store audio information digitally as a series of zeroes and ones. In digital storage, the original waveform is broken up into individual samples. This is known as digitizing or sampling the audio, and is sometimes called analog-to-digital conversion. The sampling rate defines how often a sample is taken. For example, CD-quality sound has 44,100 samples for each second of a waveform.

Sampling rate

The higher the sampling rate, the closer the shape of the digital waveform will be to that of the original analog waveform. Low sampling rates limit the range of frequencies that can be recorded, which can result in a recording that poorly represents the original sound.

Two sample rates: A. A low sample rate that distorts the original sound wave. B. A high sample rate that perfectly reproduces the original sound wave.

The sampling rate limits the frequency range of the audio file; to reproduce a given frequency, the sampling rate must be at least twice that frequency. For example, if the audio contains audible frequencies as high as 8,000 Hz, you need a sample rate of 16,000 samples per second to represent this audio accurately in digital form. This calculation comes from the Nyquist Theorem, and the highest frequency that can be reproduced by a given sample rate is known as the Nyquist Frequency. CDs have a sample rate of 44,100 samples per second that allows sampling up to 22,050 Hz, which is higher than the limit of human hearing, 20,000 Hz.

Bit depth

Just as the sample rate determines the frequency resolution, the bit depth determines the amplitude resolution. A bit is a computer term meaning a single number that can have a value of either zero or one. A single bit can represent two states, such as on and off. Two bits together can represent four different states: zero/zero, one/zero, zero/one, or one/one. Each additional bit doubles the number of states that can be represented, so a third bit can represent eight states, a fourth 16, and so on.

Amplitude resolution is just as important as frequency resolution. Higher bit-depth means greater dynamic range, a lower noise floor, and higher fidelity. When a waveform is sampled, each sample is assigned the amplitude value closest to the original analog wave. With a resolution of two bits, each sample can have one of only four possible amplitude positions. With three-bit resolution, each sample has eight possible amplitude values. CD-quality sound is 16-bit, which means that each sample has 65,536 possible amplitude values. DVD-quality sound is 24-bit, which means that each sample has 16,777,216 possible amplitude values.

Higher bit depths provide greater dynamic range.

Where Adobe Audition fits into the process

When you record audio on your computer, Adobe Audition tells the sound card to start the recording process and specifies what sampling rate and bit depth it should use. The hardware that the sound card uses determines the sample rates and bit depths that it is capable of recording. Most cards are capable of recording and playback at CD-quality settings, and often at other settings as well, such as a 48 kHz sample rate, which is common in film and video post-production. Your sound card probably has both Line In and Microphone In ports through which it can accept analog signals. The sound card samples the audio at the specified sample rate and assigns each sample an amplitude value. Adobe Audition stores each sample in sequence until you stop recording. Once you've recorded the audio, you can use Adobe Audition to edit the audio or save it to disk as a file.

When you play a file in Adobe Audition, the process happens in reverse. Adobe Audition tells the sound card that it is going to play a file, and sends the samples to the sound card. The sound card reconstructs the original waveform and sends it out as an analog signal from the Line Out port to your speakers.

An audio file on your hard drive, such as a WAV file, consists of a small header telling the audio program what the sample rate and bit depth of the audio is, and then a long series of numbers, one for each sample. These files can be very large. At 44,100 samples per second and 16 bits per sample, for example, a file includes 705,600 bits per second. This equals 86 kilobytes per second and more than 5 megabytes per minute. Stereo sound has two channels, so CD-quality sound requires a little more than 10 megabytes per minute.

Introducing MIDI

In contrast to a digital audio file, a MIDI file might be as small as 10 kilobytes per minute, so you can store up to one hundred minutes of MIDI per megabyte. MIDI and digital audio are fundamentally different: digital audio is a digital representation of a sound wave, MIDI is a language of instructions for musical instruments. A digital audio file seeks to exactly represent an audio event just like a tape recorder, whether it's a musical performance, a person talking, or any other sound. MIDI, on the other hand, is more like sheet music. It acts as instructions for the re-creation of a musical selection. MIDI files record information such as the note to be played, the instrument to play the note on, the pan and volume of that particular note, and so on. When a MIDI file is played back, the sound card takes this information and uses its synthesizer to re-create the note on the right instrument. Because every synthesizer sounds different, the MIDI file will sound different depending on what sound card plays it back. Also, a MIDI file cannot record sounds that cannot be resynthesized from short instructions, such as the human voice. MIDI support in Adobe Audition is limited to playback of MIDI files.

Conclusion

To summarize, the process of sampling or digitizing audio starts with a pressure wave in the air. A microphone converts this pressure wave into voltage variations. An analog-to-digital converter, such as those found in a sound card, samples the signal at the sample rate and bit depth you choose. Once the sound has been transformed into digital information, Adobe Audition can record, edit, alter the sound of, mix, and save your digital audio files. The possibilities for manipulation of digital audio within Adobe Audition are limited only by your imagination.