A Basic Text-Based Recording Studio
Whether you're into Metal, Jazz, Noise, Baroque or something in between, it is becoming more and more popular for artists to take on not only the roles of composer and performer, but also the roles of audio engineer, producer and even distributor of their own work.
The capability and quality of Linux audio applications are very good and constantly improving. Support for high-end and low-end audio cards is also getting better all the time. Whether it becomes the dominant platform in the field is largely irrelevant—those of us who find the flexibility of Linux and open-source tools to be valuable now have a platform suitable for creating high-quality audio tracks.
This article outlines a simple method, which may be built upon, for recording layered, multitrack recordings. In keeping with the Linux tradition, in this article, we discuss a number of small, command-line tools that perform very specific tasks very well. We then combine the power of each of these tools into a digital audio workstation. As you will see, using these tools in such a way, it is possible to overcome the (rare) shortcomings in some of these tools.
The tools we cover here are Ecasound and JACK. The Hydrogen drum machine is mentioned briefly too. We use no ALSA- or OSS-specific features directly, and either will do fine. In fact, for those who have lost their way and have strayed from the path to enlightenment (kidding), these tools and techniques also work under CoreAudio on Mac OS X.
Figure 1 shows how data flows between each of these components at a high level.
For the examples outlined in this article, any sound card will do. I even have performed some relatively acceptable recordings using the onboard Intel i8x0 sound device in one of my Linux laptops. However, the difference between lower-end audio controllers and the mid- to high-end ones is quite noticeable.
We also require a Linux distribution. If you have trouble getting JACK and Ecasound for your distribution, try the AGNULA live distribution. Most distributions come with the relevant packages these days anyway.
A mixer is desirable. Using a small (read: cheap) mixer may give you more flexibility and a chance at better sound. You also may find that a direct injection box or a microphone preamp is adequate.
Note that Figure 2 suggests plugging the headphones in to your Linux box. Most mixers allow the sound card to be plugged in to a signal return port and allow the headphones to receive the audio signal either before or after the signal is sent to the Linux box. This is acceptable too.
In this article, we don't assume much, apart from needing the following:
A Linux box with a configured and tested audio controller.
The ability to source and install necessary packages and their dependencies.
A familiarity with your choice of noise-making device (for example, guitar, cello, cat and so on).
JACK, which stands for the JACK Audio Connection Kit, is an API and a service that provides audio connectivity between applications on many POSIX-compliant systems. JACK has been designed with low-latency communication in mind.
Many of the examples in this article may work equally well without JACK. I personally have had fewer audio dropouts on systems employing JACK running with real-time priority than without, and it is quite useful for interconnecting audio applications, such as the Ecasound and Hydrogen examples discussed later.
For applications to make use of JACK, they must be linked against the JACK API libraries, and the JACK service, called jackd, must be started. Distributions shipped with JACK often already have most applications linked against the JACK API. If not, consult the build or compile instructions for your given application.
To start the JACK service, execute a command similar to the following:
jackd -R -d alsa
The -R option instructs JACK to attempt to attain real-time privilege, and -d alsa instructs JACK to use the ALSA sound system. For users still using the OSS sound system, -d oss should suffice, and -d coreaudio should get Mac OS X users off to a start.
Each driver supports a series of driver-specific options. These may be viewed by specifying --help after -d alsa.