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Editing ACID Loop Properties with Sound Forge
Written by Scott R. Garrigus - © 2006, Cengage Learning. Reprinted with Permission.
To prepare your sample loop for use within ACID, you need to use a special process. This process involves adding extra information to the audio file. To do this, you must use the Edit ACID Properties dialog box by choosing Special Edit ACID Properties.

In the dialog box, you'll notice a number of different options and parameters. By choosing the appropriate settings, ACID can determine the correct way to handle your sample loop when you load your loop into an ACID project.

The first available option in the Edit ACID Properties dialog box is called One-Shot. If you want your sample loop to play once rather than looping over and over again, this is the option to choose. A One-Shot sample does not get time-stretched along with the tempo changes of an ACID project, and the sample's pitch does not change along with key changes in an ACID project. A good example of a One-Shot sample is a drum set cymbal crash.

The second available option in the Edit ACID Properties dialog box is called Loop. This is the option to use if you want your sample loop to play over and over again, such as a looping bass guitar riff. Sample loops that are designated as Loops in ACID are time-stretched and their pitch changes along with the tempo and key changes of an ACID project. In order for ACID to change the loop appropriately, it needs to know the initial tempo and pitch of the loop.

Number of Beats
To specify the tempo of your loop, simply enter the number of musical beats the loop contains into the Number of Beats parameter. You can figure out how many beats are in your loop bycounting off while you listen to it play. I'll give you an example later in this appendix. One thing to note is that if you enter the wrong number of beats, ACID does not play your loop at the proper speed. For instance, if your loop contains 16 beats but you enter 8 for the Number of Beats, ACID plays back your loop twice as fast as the loop should play.

Root Note for Transposing
To specify the pitch of your loop, simply enter a note value into the Root Note for Transposing parameter. This root note is the original pitch at which your sample loop was recorded. You need to know this beforehand, or you'll have to figure it out manually by using a tuner.

One other thing to consider is that if you want your sample loop to be time-stretched but not transposed (such as would probably be the case with most percussion-based loops), you can choose the Don't Transpose option for the Root Note for Transposing parameter.

ACID 2.0 Disk-based
Most of the sample loops that are used in an ACID project are played from your computer's memory, but if you have some really long samples (such as an entire vocal track), you might not have enough memory in your computer to use those samples. In this case, you can specify that ACID play your sample by reading it directly off your hard disk drive. To do that, simply select the ACID 2.0 Disk-based option in the Edit ACID Properties dialog box. Disk-based samples cannot have their pitch transposed, but if you specify a tempo, you can make it so that ACID time-stretches the samples. To do so, just enter a tempo (in beats per minute) for the sample into the Tempo parameter. You need to know the tempo at which the sample was originally recorded.

ACID Beatmapped
If you are using ACID 3.0 or later, then you have an additional option at your disposal. The ACID Beatmapped option is similar to the ACID 2.0 Disk-based option, meaning it is used mainly with really long samples. The difference is that in addition to time-stretching, you can have ACID Beatmapped samples transposed according to the ACID project pitch. Simply set the Root Note for Transposing option (as explained earlier for the Loop option). And, of course, set the Tempo option for time-stretching. One additional option lets you specify where the downbeat (or first beat in the first measure) for the sample occurs. Most often, you'll probably leave this set to zero.

Preparing an ACID File—A Step-by-Step Example
Now that you know about all of the special ACID tools that Sound Forge provides, let's go through a step-by-step example on how to actually use them to prepare a file.

1. Choose File > Open (or press Ctrl + 0 on your computer keyboard) to display the Open dialog box. Select your file. For this example, let's use one of the files that is included with Sound Forge. Select the file called Fill.pca. Click Open.
2. Press the spacebar on your computer keyboard to play the file. It's a drum fill sample loop. Because it's not a single instrument sample that might just play once, we can rule it out as being a One-Shot sample. And because it's easily small enough to be played from within your computer's memory, we can rule out that it is an ACID 2.0 Disk-based or ACID Beatmapped sample. That means we'll be designating this file as a Loop for ACID. Before we edit the ACID properties for the loop, we need to figure out how many beats it contains. Play the file a few more times and see if you can count out the beats.
3. Select Special > Edit ACID Properties to open the Edit ACID Properties dialog box.
4. Choose the Loop option.
5. For the Number of Beats parameter, type in 4. Did you guess it correctly?
6. Because this is a percussion loop, there's really no pitch involved, and we don't want ACID to transpose the loop by mistake. So, for the Root Note for Transposing parameter, select Don't Transpose.
7. Click OK.
8. Save your file in the WAV file format.

TIP: Save The Metadata
When you save your newly ACID-compatible file, be sure to activate the Save Metadata with File option in the Save As dialog box. If you don't do this, the special ACID information that you entered in the Edit ACID Properties dialog box is not saved along with the file. In addition, not all file formats support saving metadata, so it is best to use the WAV file format when creating files for ACID.

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