A Survey and Intro
If you're not familiar with the area of Linux audio editors, you might be totally amazed at just how many there are. Clearly, writing these has scratched more than a few itches and more than one has earned grades as a class project.It's not too hard to figure out why the area has been popular. For one thing, mangling sounds is fun, and for another, there is endless scope for playing with DSP algorithms. You can do that these days without writing a whole editor, but we'll get to that in a moment.
First of all, what is an audio editor, or better, an audio file editor, and what are they used for?
When audio is recorded on a computer, the information is stored in one of a number of formats—most commonly WAV or AIF on Macs. Both are uncompressed and have various options concerning quality and file size (higher quality = bigger file size), which needn't concern us here. There are also compressed formats that, by means of different algorithms, make the file sizes much smaller. Two well-known examples include MP3 and Ogg, which are lossy (information is discarded in the same sort of way as with the picture format, JPG), and a newer one, FLAC, which is not.
This information can be (and usually is!) depicted as a time/amplitude graph, where time runs along the horizontal axis and the frequency and amplitude (loudness) is mapped vertically. This presents pretty pictures of sound that you most likely have already seen and are intuitively easy to read.
Basics of Editor Actions
We use audio editors to perform a number of tasks, the simplest of which is a cut. If, for example, a file is too long, we highlight the area we want to remove by using the mouse and then we, typically, go to Edit and Cut in whatever app we're in, and zap it.
Let's look at the real-life situation of a podcast to see what sorts of things we might do. Let's say we've recorded an interview over the phone that we want to add some music bits to later.
As usual with phone recordings, we might have to deal with noises on the line, volume irregularities, and the usual interview problems of ums, ahs, and thinking gaps. Exactly what you do with these is an editorial choice, and I won't say more other than that making absolutely everything punchy is found by many thinking people to be nauseating.
After a run-through, the first thing that might be done is the pruning. Here it pays to know about destructive and non-destructive editing. The first operates on your primary file and any cuts you make are gone forever. The second method copies everything as its title suggests. Making copies of your own with destructive editors is easy to do though—you just have to remember.
The next thing to do might be attending to noise levels. Quite frequently this will entail just judging whether bits are usable or not, as denoisers often require a little luck.
How about levels generally? Here the normalizer is beloved of quite a few people, but the real answer, quite often, is careful and time consuming fiddling about with areas of the file.
Finally, you might want to export the file in a different format from the one you started with.
In this sort of straightforwardish case, we haven't played at all with another aspect of editors—adding effects.
Effects
Effects are fun and sometimes even useful. In the podcast example above, for example, we might have added a touch of reverb to give the voices a little extra life.
There are many, many, different kinds of effects and within kinds there are different approaches and results. In the field of electronic music making, files might be prepared for looping, or other use, by mangling them substantially. For example, if you use the Linux app Loopdub to play loops, there are limited facilities for live file mangling, so they need to be prepared beforehand.
In App
In the old days, if you wanted to write code for effects, it needed to be in the body of the app. These days, there is JACK, an audio interconnection kit, and LADSPA, a plugin format, so you can write and use effects where this system is relevant and possible.
In Line (LADSPA-JACK)
Live editing is a different area that is used mostly by musicians. For example, one might use Csound to generate sounds which are sent to the JACK tunnel and a series of LADSPA effects. All of this might then be routed (and recorded) by the HDR app, Ardour.
In this sort of way, JACK-capable editors can be used to at least add effects in real time. Mostly though, we don't want to do that.
Some Editors
Earlier, I said there were an amazing number of Linux audio editors out there and there are, but here I'm going to look at a representative sample.
Audacity - Most Used
Audacity is the most well-known of the Linux audio editors. One reason is that it has been ported to both the Mac (OS X) and Windows. When podcasting first began to be a big thing, this app was something that people could point at that would get the job done and was free.
It has a simple but attractive interface and pretty much everything you can do is intuitively obvious for anyone who has even a slight knowledge of what is going on.
As is quite usual for editors, there are also recording facilities and the number of tracks that can be handled will be determined by your soundcard. It is worth saying here that the Big Guy, as far as recording is concerned, is Ardour. Check it out if you have ambitious schemes in mind.
Snd - The Grandad
Snd is the editor with the longest history and was, for a while, nearly the only one capable of sophisticated transformations.
The original idea was that its construction would be modelled on emacs in that it could be infinitely extensible using scripting languages. It is exactly that and could suit DSP experimenters who have a certain sort of comp sci background or who have those tendencies!
In any case, this is a well-respected piece of software that is still being added to.
Sweep - Tricks
In addition to the usual editing tasks, Sweep can also be used as a performance tool. A feature of high-end commercial editors, such as Sountrack Pro is the ability to hear samples as you move around in the file, without having to hit the play button. This is useful while editing, but the Sweep team has given this idea the name of Scrubby with the further idea that it will be used for digital DJing. In fact, there are other performance tools in Sweep, such as the ability to play many loops and control the play with the computer keyboard. I haven't seen anyone using it in performance, yet but maybe mentioning this aspect here will get more people interested.
If you're interested and will be in Europe in March/April 2008, maybe you should check out Bleepfest, which I have something to do with. A footnote here is that Linux based musicians have been actively encouraged to take part (three events so far, in London and Berlin with the next most likely in Paris), but it is has been a 99.9 percent Mac affair so far.
Traverso - Context
Traverso aims to be a complete digital audio workstation (DAW) but has significant editing skills and is the newest of the projects listed here. It is also available for Mac OS X and Windows.
It is interesting in a few ways. For a start, the Unix way is to have many interconnected small tools rather than enormous apps that do everything. Ardour, for example, purposely has less in the way of editing capability precisely because they are following this philosophy. Traverso is taking a different tack as they feel that it is easier for people to download, install, and learn one app, than it is to discover and learn a whole collection of apps.
Another thing the developers were interested in was the area of menus, and they have made efforts to extend commands by using the mouse in conjunction with the keyboard. This approach can potentially both enrich and speed up the user experience but won't be loved by everyone.
Conclusion
There is a rich amount of choice available in this sector. Perhaps you can find something that not only suits your needs but also leads you off to some interesting new places.
John Littler is chief gopher for Mstation.org.
linux audio editor with unique tricks (LPC anal/synthesis)
2007-11-29 13:01:40 josquin [Reply | View]
Linux audio editor with unique tricks: (LPC analysis/resynthesis & other analysis methods)
http://www.create.ucsb.edu/~doug/htmls/MiXViews.html
njoy
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