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How To Guides: Timebases in ProTools
Written by Andy Patterson
So, there are two different time bases in Pro Tools. You’ve heard people say it, but what does it actually mean?
When you create a track in PT, it basically assigns it to a certain timebase. By this we mean it follows a certain scale with reference to time.
There are:
Sample based tracks
and
Tick based tracks.
The difference between the two is the way that any material on that track behaves, with reference to the timeline.
Let’s look at the timeline, and what it represents.
There are a variety of displays one can use for the timeline in ProTools (the timeline being the horizontal visual representation of the passing of time).You can view it as Samples, time (minutes and seconds), Timecode (hours, minutes, seconds, frames) and a few other specialist (feet and frames for film work).
You can also view Bars and Beats. There is an important difference between some of these.
Time based views are fixed. For a 44.1kHz session, there will be 44100 samples each and every second. Every minute will be made up of 60 seconds and every hour of 60 minutes. This is a given and is fixed for that sample rate.
Bars and beats however are not fixed due to the feature of ‘Tempo’. Tempo is the rate at which music is played. So, for a piece of music at 60 BPM (or beats per minute) at a time signature of 4/4, there will be 15 bars of 4 beats over one minute.
At 3/4 there will be 20 bars of beats (3 each bar). This minute retains its (44100 *60=) 2646000 samples in that time.
Another example is that at 120BPM, there will be 120 beats in our minute. Split into bars of 4, this equals 30 bars (twice the tempo means twice the number of bars will be present in the same time).
So, really, the tempo map of these bars and beats is a moveable and changeable visual grid on top of the fixed time and samples grid.
How and why is this helpful? well….
Sample based tracks
When you create an Audio track or auxiliary, it automatically sets the timebase of that track to be a sample based track. This means the following:
It will follow the sample based grid. Any changes you make to the tempo will not affect the audio at all.
Tick based tracks
However, when you create a MIDI track or Instrument track, it sets it to be a ‘Tick Based track’, which means the following:
It will follow the bars and beats timebase. Any changes you make to the tempo ‘Grid’ will effect the rate at which the midi data is played.
For Example
you create a MIDI track and record one note per second (with the tempo for the session set to 60BPM). Therefore you will play 60 notes over the course of 1 second.
You also create an audio track and record yourself counting 1 – 60 over the course of that minute.
So you have two recorded regions, both lasting 60 seconds.
You now change the tempo at Bar 1 to be 120BPM. As soon as you press enter the MIDI region will immediately half in size. That is because it follows the tempo grid by default. The audio track, which is sample based stays exactly as it was. So your 60 midi notes now play in half a second.
If however you undo that tempo change and make the MIDI track into a sample based track there is a little button in the track header as shown in the screenshot (the audio track is in sample based, whereas the midi track is tick-based).
Now, change the tempo to 120, you will notice that it has no effect on the MIDI region. In this instance it is following the fixed samples grid and not the tempo grid.
Why is this useful at all?
Well, say you record a bit of music without a click track. The tempo of the piece may vary as a natural process. You’ve recorded your drum track as MIDI performance data onto a midi track. You now want to make the tempo map follow the song, so you can clearly state the bar numbers to musicians to come in at different places.
(or you want to have synchronised delays happen in your mix).
If you now start changing the tempo, the (tick based) drum track will immediately go out of time with the other instruments which are on the sample based tracks. If before you change the tempo you set the MIDI track to be a Sample based track, then you can adjust the tempo without losing the timing information of the drum track.
Then once you have the tempo map done, you can change the timebase of the MIDI track back to tick based to make any changes to the song as a whole.
There will be more info on how to create a tempo map in a future How to Guide.