This new file will be used as the target to build the beatmapped song. Once you are happy that your selection loops seamlessly, Copy it to a new wave file with Ctrl+C, Ctrl+E. If you Beatmap the song in ACID first, this will give you a good indication of how soon tempo drift will occur. The object is to make your selections just as large as the amount of time it takes the song to drift off tempo, but no larger. You may try and select two or more measures if you think they will stay on the beat. These vertical lines should line up fairly close to your markers. Turn on the Selection grid lines button from this toolbar to see the beat grids. There are icons on this toolbar to Shift Selection Right which we will be using a lot in this procedure. Turn on the ACID Loop Creation Tools toolbar ( View > Toolbars... > ACID Loop Creation Tools) to be able to see the BPM readout from your selection. Looping at the zero crossing will help eliminate clicks or pops at the loop point. This will ensure that all cuts are a zero crossings.
If you hear clicks or pops, make sure you use either the ‘ Z’ key to snap your selection to the zero cross points, or use the menu Options > Auto Snap to Zero (Ctrl+B). Fine tune the ends of the selection so that the measure loops perfectly when played as a loop in Sound Forge. This should encompass the four beats of the first measure. Once several measures have been marked, stop and make a selection from the first marker to the fifth marker. Do this for a few measures to give you a visual cue of the beats in each measure. To do this, play the file and tap the ‘ M’ key on each beat. I like to start by mapping the tempo of the file with Markers. ( View | Toolbars… | ACID Loop Creation Tools) Tip: Turn on the ACID Loop Creation toolbar in Sound Forge to assist in working with ACID Loops. Delete the temporary wave and repeat at step 2 until the entire file is mapped.Append the temporary wave to the target wave.Time-stretch the temporary wave to match the song’s BPM.Copy and paste to a new wave to a temporary wave.Make a loop selection of one or more measures in duration.Open the source wave file to be beatmapped in Sound Forge.Then append each measure to a new wave file to create a new file that is perfectly locked to the tempo. The procedure in Sound Forge involves slicing the original song into measures and time-stretching each measure to be a constant length. Creating that many beatmaps in ACID is just too time consuming. Sound Forge has an optimized workflow for working with sound files at this level or granularity where each measure may have to be corrected. In these extreme cases you can fix tempo drift in a wave editor like Sound Forge. Sometimes you want to use a live recording in ACID but the Beatmapper can’t be used effectively because the tempo drifts several times throughout the song.