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This article was written back when 7.4 came out (introducing elastic audio), but is still equally relevant in Pro Tools 8 as these features haven’t changed much.
Elastic Audio Part 2:
In the last installment of the Pro Tools corner we took a first look at 7.4’s incredible new elastic audio feature. This week I want to dive a little deeper into the topic, showing you how to easily quantize and warp audio directly in the timeline with incredible accuracy and sound quality.
Quantizing audio regions elastically:
The beauty of elastic, “tick” based audio is its ability to re-conform itself much like MIDI data, making tempo changes and quantization (or re-grooving) a breeze. What use to take hours of laborious editing time can now be done in a few clicks, and still sound better then doing it the old fashioned way with beat detective.
To quantize an audio region:
Manually warping audio events:
Sometimes, rather then quantizing an entire selection of audio events, all you want to do is manually shift an event slice one way or another. In this case, Pro Tools allows you to easily create and shift warp points within a region manually. For example, you may want to carefully manipulate the timing or feel of a vocal track, a common situation where an outright quantize would yield less then satisfactory results.
To editing a regions warp points:
If you ever need to remove the warp properties from a region and revert back to the original copy, simply right-click on the region and choose “remove warp.”
Correcting Transient Analysis:
The secret behind Pro Tools ability to stretch, shrink and quantize audio regions accurately lies in its transient detection, or the ability to identify rhythmically significant points within a file. If Pro Tools is detecting too many erroneous transient points, you can edit a regions “event sensitivity” via the region’s “elastic properties.” Adjusting the detection sensitivity is similar to using the sensitivity slider in beat detective, lowering the sensitivity on material with complex waveforms and poor transient definition can help remove excess analysis points (ie: vocals, complex synth patches, etc).
To edit a region’s elastic properties right click on the region and choose “elastic properties.”
In the rare case that a region’s transients are not properly identified and adjusting the event sensitivity doesn’t help, you can manually edit a region’s analysis using the grabber tool inside the track analysis view.
To manually correct or modify analysis:
Because editing analysis points on complex polyphonic material can be quite tricky, start by practicing on rhythmic material with clearly defined transients.
This entry was written by , posted on October 14, 2009 at 6:21 pm, filed under Articles, PT Corner and tagged editing, elastic audio, pro tools, PT Corner. Leave a comment or view the discussion at the permalink and follow any comments with the RSS feed for this post.
This article was written back when 7.4 came out (introducing elastic audio), but is still equally relevant in Pro Tools 8 as these features haven’t changed much.
Introducing elastic audio:
A few weeks back we took a first look at some of the new features available in Pro Tools 7.4, the most notable being elastic audio, or the ability to stretch and squeeze audio regions automatically in the timeline. After spending some quality time with the new features, I must say that elastic audio is simply amazing and will definitely transform the way you work in Pro Tools and save you hours of time. While there are surely an endless number of uses for elastic audio, this week I want to walk you through a basic audio loop workflow inside Pro Tools 7.4.
Elastic Loops
One of the greatest features added in Pro Tools 7 was the ability to drag and drop audio content from the finder or windows explorer directly into your session, allowing you to quickly add loops and audio samples from anywhere on your hard drive. While this was nice, the usefulness of audio loops has always been limited to the source material’s tempo, unless you want to spend the time using beat detective or manually conforming the audio material to your session’s tempo. Now, by taking advantage of 7.4’s elastic audio engine, not only can we drag and drop our favorite loops directly into a session, but these loops will also re-conform themselves automatically to the session’s tempo map.
If you have ever used apple loops in logic or garage band, or worked with Abelton live, you may already be familiar with the benefits of an elastic timeline. The workflow that I am about to show you will help get you started with elastic audio in Pro Tools, as well as showcase some of the unique elastic time features inside 7.4. Remember, to complete this example you will need to have Pro Tools 7.4 installed on your system, as the techniques I am about go over will not work in previous versions.
Example: basic elastic audio workflow in 7.4
I have prepared for this example by first creating a new blank session into which I will import and time my audio loops. I have chosen a few different loops to work with in this example (a simple drum, bass, and percussion loop), but almost anything will work. As you start to experiment with elastic audio, you may want to try working with rhythmic tracks first, as their transient detection confidence is very high and they can be re-timed relatively easily.
Step 1: Setting up
Before I begin, I want to check a specific option location in the processing tab of Setup > Preferences called “enable elastic audio on new audio tracks.”
Step 2: Importing the first loop
To import my first loop (a drum loop) into my session, I can simply drag and drop the file from my finder (or window’s explorer) into the tracks list in Pro Tools. A new track will automatically be created, and since this is the first file to be imported Pro Tools will ask me if I want to import the tempo from the loop.
In this example I will go ahead and choose “import” from the dialog. Pro Tools will now adjust the tempo ruler to match the extracted tempo from the audio loop.
Step 3: Selecting tick based audio
Because audio is generally sample based (), Pro Tools defaults the track’s time base to samples. When using elastic audio in conjunction with tempo changes, I want to change the track’s time base to “ticks” (
) by clicking on the track’s time base selector.
Now I can change the session’s tempo and all tick-based tracks will follow the tempo ruler just like MIDI events.
Step 4: Previewing new loops
Now that I have the tempo extracted from the first loop, I want to preview some new loops at the current session tempo, before adding them into the session. To do this I will browse and import my loops from the workspace browser, located under Windows > Workspace.
To preview the loops at my current session’s tempo I will click the “audio files conform to session tempo” icon in the workspace browser.
To preview a loop in the workspace browser, simply select the file and hit space bar or click on the preview icon. Note: you can choose to preview with loop playback or activate auto-preview by checking those options in the browser menu.
To import a file from the browser I can again just drag and drop it into the tracks list. A new track is created and automatically set to ticks with elastic audio enabled. I can continue to preview loops and add them into my session all at the same tempo, regardless of the loop’s original tempo.
Notice the elastic audio icon in the top right hand corner of the region, and next to the region name in the region’s list.
Step 5: Changing the tempo
Now that I have imported a few loops and set them up to re-conform as elastic audio, I can easily change the manual tempo in the transport or even add tempo events in the tempo editor. Notice how the regions squeeze and expand to match the bar|beat grid.
Quality considerations:
Now is probably a good time to discuss some of the fidelity considerations when stretching or shrinking audio files. While the elastic audio algorithms in Pro Tools are very good, as a general rule of thumb you don’t want to stretch or shrink your audio too much (your ears will tell you how far you can go). You can help the process out a bit by selecting the appropriate plug-in algorithm from the track’s elastic audio drop down menu. Pro Tools features 5 different base algorithms to choose from: Polyphonic, Rhythmic, Monophonic, Varispeed, and X-Form (rendered only). While a complete breakdown on the differences between the algorithms is beyond the scope of this article, try experimenting. Start with the appropriate algorithm for the type of audio you are working with and then try out different presets, listening for any changes.
More elastic audio coming up:
We have only begun to scratch the surface of elastic audio in Pro Tools. Stay tuned for elastic audio: part 2 with more tips, tricks, and tutorials on this amazing new feature.
This entry was written by , posted on at 6:00 pm, filed under Articles, PT Corner and tagged editing, elastic audio, pro tools, PT Corner. Leave a comment or view the discussion at the permalink and follow any comments with the RSS feed for this post.
Once hailed as game changing and certainly one of Pro Tools’ most buzz worthy features, has beat detective officially reached legacy status?
Yes and no. While elastic audio and tick based time references for audio tracks have made life easier for many editors, in some instances literally cutting the time it takes to complete a task by ten fold or more, I firmly believe beat detective still has a place and time (no pun intended) in a Pro Tools, at least for now.
BD or Elastic Audio?
Essentially, all beat detective really does is “detect beats” or transients of audio material (usually drums, percussion or monophonic bass/guitar). Once these “triggers” have been detected, the user has some options. Traditionally, slicing or separating a larger region’s transients into individual smaller regions and then subsequently “conforming” or quantizing these slices to the grid was beat detective most commonly used workflow.
This usually works OK, but can manifest problems worse than the bad timing was in the first place. Because beat detective physically cuts and moves regions (thus maintaining absolute phase accuracy in multi-track scenarios like drums) the gaps resulting after a conform are a neccissary evil of the process. While these gaps can be filled and cross-faded inside beat detective, many times the process of trimming the conformed regions reveals the decay of the previous note (this is especially the true when notes are extremely rushed or ahead of the beat, or when you are trying to add swing to an originally straight feeling performance). Often what engineers are forced to do is manually address these problem spots one at a time, usually pasting an alternate hit over the un-trimmable section (either from another part of the session or from samples taken from the kit during recording). This can take several hours, depending on how out of time the performance is and how often manual intervention is required. I personally have had sessions where completely rebuilding a section of drums manually with samples from other parts of the session was a faster option than trying to use beat detective. At which point I usually say to myself, “It would have been cheaper to rebook the studio, hire a better drummer and re-record the drums.”
Much of what was once done in beat detective has been replaced by the elastic audio feature set. Because elastic audio “warps” or stretches notes into time, no gaps are created when quantizing or conforming audio to a different feel, and since the “rhythmic” elastic audio plug-in is essentially just adding or subtracting space in between hits, you generally don’t have to worry about the “zipper” artifacts that plague granular re-synthesis based warping.
Some engineers argue that unlike beat detective, elastic audio can’t maintain perfect phase coherency across multiple tracks because the algorithm processes each track uniquely. While this is true, you can get around this somewhat by grouping the tracks before elastic analysis and processing, this method will try to maintain phase coherency as much as possible as audio is stretched. I generally find this group method yields usable results almost every time, and while I do hear very subtle differences in the phase alignment of the kit, they are so subtle that the cost of doing a 4 to 8 hour beat detective session wouldn’t warrant the improvement (nor be affordable or in the best interest of the client).
Like beat detective, I find that working with small sections (4-8 bars) at a time yields the most accurate results when conforming with elastic audio. This allows me to focus and address any errors manually as I work through the song. I generally do not try to conform fills and opt to manipulate them by hand, as the timing during these sections is often dramatically different than a grid quantize would suggest. For bass, I generally avoid automated conforming altogether and adjust each note by hand with warp markers.
Groove Extraction
All that said, I still haven’t fully addressed the question, “is beat detective dead?” For quantizing drums and other percussion, pretty much. At least for my workflow it is. Simply put, time is money and elastic audio saves me lots of time and sounds really good if you know how to use it. But I still use beat detective almost daily for it’s lesser known feature, “groove template extraction.” Groove template extraction uses the same process of detecting beat triggers but instead of separating/conforming those triggers it records them to a groove template. A groove template is essentially a list of tick offsets from the grid, with a goal being to extract the groove of one things and apply it to another. For example, if the “and of four” is slightly behind the beat, a groove template would record the exact number of ticks that note was from the grid point (…|4|480). Subsequently, when I quantized something with that groove template, the off-beat of 4 would be pushed back a bit. If I had to imagine a groove template as a text file, the following 1 bar template would describe a swung 8th note feel:
Grid: 1|1|000 Offset: +0 ticks
Grid: 1|1|480 Offset: +100 ticks
Grid: 1|2|000 Offset: +0 ticks
Grid: 1|2|480 Offset: +100 ticks
Grid: 1|3|000 Offset: +0 ticks
Grid: 1|3|480 Offset: +100 ticks
Grid: 1|4|000 Offset: +0 ticks
Grid: 1|4|480 Offset: +100 ticks
When beat detective is in groove extraction mode, it measures the difference from the triggers it detects to the tick grid and records them either to the groove clipboard or a new groove template. At that point, I personally would use elastic audio to quantize another region with the newly created groove template.
In this workflow, there is a sort of symbiotic relationship between beat detective and elastic audio, at least until Avid integrates groove template extraction into the elastic analysis engine (I believe sonar has a feature like this in its elastic implementation). I imagine an elastic audio system that would allow me to let’s say, click on a menu and see a list of every other elastized track and choose “quantize to follow track XYZ.” At which point the warp markers of one track would reconform to match the analysis (or warp markers) of another track in the session.
Bar Beat Marker Generation
One additional usage of beat detective is it’s bar|beat marker generation mode, which is specifically designed to conform a session’s grid to a freely recorded piece of audio. It is sort of like reverse groove template extraction, where audio that may not conform to any one tempo is assigned a grid based on the transients absolute sample position. Think of a performance and it’s transients representing specific beats of the music (1,2,3,4 etc). Now imagine the grid is flexible and all you have to do is place a push pin at each transient marking what bar|beat it represents. In this scenario, Pro Tools switches the tempo ruler to bar|beat marker mode and every pair of bar|beat markers may represent a change in tempo. Remember, you are not conforming or quantizing the audio, it is the grid itself that is moving. A freely recorded piece of music that may sound consistent will still have small tempo changes, maybe a fraction of a BPM per measure.
Most would ask, “why on earth would I want to conform the pro tools grid to my audio, and not conform my audio to the grid?” Say you have a session that was not recorded to a click, but you like the feel and want to add additional MIDI and/or do some editing. Your options are either to work completely in slip mode (without the ability to quantize additional MIDI performances), or to develop a bar|beat grid based on your freely recorded audio. The people who track notes for guitar hero and rock band have to do this kind of stuff all the time, as most of those classic songs from the 70s and 80s were not recorded to a click and creating an accurate control track requires MIDI with many tempo changes over the course of the tune.
Identify Beat
An alternative to Beat Detective’s bar|beat marker generation is Event>Identify beat, which uses the same concept of sample based bar|beat markers to develop a grid around a freely recorded session. The only difference here is that you will use tools like tab to transient to place the cursor and identify beat to manually insert a bar|beat marker into the session. I actually prefer this method over beat detective as it gives me a lot more control and I can generally get a song mapped (placing one marker per measure) in under 10 minutes.
In Closing
While the sonic purist may still consider using beat detective for mult-track drum timing, and certainly every unique situation calls for a slightly different approach, over the past 2 years elastic audio has definately taken a big bite out of my beat detective work flow. I will of course continue using beat detective for groove template extraction until a faster solution is implemented, and I will probably always use indentify beat when mapping out free performances, but for the most part I am glad to leave those aweful gaps and tediously long editing session behind.
This entry was written by , posted on at 3:32 pm, filed under Articles, featured and tagged beat detective, editing, elastic audio, pro tools. Leave a comment or view the discussion at the permalink and follow any comments with the RSS feed for this post.
