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"The Sequence of Events"

For example, replacing basic drum tracks on a live recording is the kind of chore that only the bravest audio engineers attempt. After all, unless the drummer is fueled by machine oil rather than beer, tempos are likely to drift, making it difficult to overdub a completely new drum track. However, using MIDI, it's possible to replace these original acoustic drum tracks with synthetic drums while maintaining the tune's live feel.

In the steps that follow, I talk about using Opcode's Studio Vision Pro to replace drum tracks, but you can use any professional sequencer, such as Mark of the Unicorn's Performer, Steinberg's Cubase VST, or Emagic's Logic.

To turn drum tracks on your tape into MIDI notes, you must route the audio signal to the proper destination. Additionally, the tape deck and sequencer must be in sync. Here's how to make all the right hookups.

The sequencer depends on time code to sync with the tape deck, so if you don't already have time code on the tape, stripe your tape with SMPTE. To send the SMPTE track to the sequencer, patch the tape deck to your MIDI interface's SMPTE input port via the mixing board.

Now send the taped drum tracks to the drum module by patching the kick-drum track from the mixing board into the first trigger input on the drum module and the snare-drum track into the second trigger input. (At press time, Alesis [310/255-3400, ] was the only company that offered drum modules with trigger inputs.) Be sure to assign a different MIDI note value for the two triggers–for example, have trigger 1 output MIDI note number 36 (C1, the note name associated with a General MIDI kick drum) and trigger 2 output MIDI note number 38 (D1, the note name associated with a General MIDI snare drum).

Play the tape to adjust input levels on the drum module. If the MIDI drums trigger too readily or fail to trigger on quiet notes, adjust the input sensitivity on the drum module and the output on the mixing board. It's better to err on the side of triggering extra notes–you can fix those later by filtering out notes below a certain velocity (see Step 2).

•Multitrack tape deck
•Mixing board
•Drum module with trigger inputs
•MIDI interface with SMPTE
•Professional MIDI sequencer

•The reclocking technique employed in Step 3 can easily be applied to a freely played piano solo in which you wish to add–and quantize–more instruments.

•Skip the click track altogether if you have a steady, rhythmic track–such as a MIDI bass-guitar part or the left-hand portion of a piano part. Just copy that track, strip out those notes that don't outline the beat, and apply the Reclock command to that track.

March 1999 page: 105

Step 1: Set Up Your Sequencer

Once you set up your MIDI system (see the sidebar " The Right Connections "), the next step is to configure a sequencer, such as Studio Vision Pro, so that it records MIDI from the correct source and syncs to the time-code track.

In Studio Vision Pro (which I'll refer to as Vision), choose Enable Input Devices from the Setups menu and select the drum module as an input device. This ensures that Vision records MIDI information generated by the drum module. Select MIDI Timecode as your sync source, and choose the Wait For Note option so that Vision starts recording when it detects the first MIDI event. Record-enable a track in the sequencer–this will be your MIDI drum track–and select the drum module as the instrument source. Press Vision's record button, and start the tape a few seconds before the beginning of the tune to give the tape deck and sequencer time to sync up. Play the tune all the way through, and stop the tape at the end. The MIDI kick- and snare-drum parts should now appear in the track.

Step 2: Filter False Triggers

Drum triggers are not as accurate as the human ear and usually only approximate a drummer's performance. In this step you'll use a filter to remove the most obvious extra notes.

When triggers misfire, they sometimes play repeated notes. These notes are often quieter than the ones you want to keep. To clean out most of the unwanted notes, use a filter to remove those that fall below a certain velocity. For example, if most of your snare hits have a velocity of 90 and over, create a filter that selects only the notes with a velocity of 80 or less and then delete those notes. Now play back your track and delete any stray double-hits that escaped the filter. Insert any notes that weren't recorded.

Step 3: Turn the Beat Around

If your only goal were to replace the kick and snare on your live track, you'd be nearly done. All that would remain would be to tinker with the velocities and timing of the MIDI drums and record these MIDI tracks back to tape. But why stop now when you have the opportunity to make your upcoming MIDI overdubs easier by following one more procedure?

If you glance at the kick and snare parts, you'll notice that they don't line up with the sequence's bar lines and beats. This means that you won't be able to quantize (align notes to a rhythmic grid) additional MIDI parts with beats and bar lines, much less quantize the kick and snare parts you've just recorded. Therefore, you must impose order on these bars and beats by moving the sequence's bar lines to match what the kick and snare are playing. You'll do that by creating a click track and using Vision's Reclock command to create a new tempo map based on that click track. If necessary, then move the drum parts so that they begin at the right time. Here's how.

Rewind the tape to the beginning of the song, record-enable a new MIDI track, and select a MIDI controller–a MIDI keyboard, for example–to record notes into that track. Choose that controller as your input source. Press Vision's Record button; start the tape; and on the controller, play a single note–middle C, for example–on each quarter note. Continue tapping out quarter notes until the tune ends. A steady stream of quarter notes should appear in the track you just recorded. Now listen to the tape with your quarter-note accompaniment. If there are gross timing errors, fix them.

The track you just recorded is the outline for your new tempo map–it establishes where the beats and bar lines go. To create the tempo map, select the notes in this track and choose Vision's Reclock command. The sequencer now creates bar lines and beats around the notes you played.

Reclocking sometimes causes the sequence to shift in time–throwing it out of sync with the tape. If the sequence is horribly out of sync, use the sequencer's offset command to shift the sequence forward or backward in time. If it's just a little off, consider using your sequencer's Play Shift function to incrementally move the snare- and kick-drum beats forward or backward.

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