Portable Hard Disk Recorder How-To

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Use an old laptop to build a multitrack hard disk recorder.
Distribution Considerations

As mentioned previously, multitrack audio recording ideally requires real-time access to the hardware, but this support is not built in to the kernel by default on most Linux distributions. It's an option that must be enabled at compile time, or, if you're running an older kernel, must be hand-patched into the source before compiling. Although I have no problem recompiling my kernel for a good cause, it's not something I like doing for the sake of pure amusement.

Fortunately, a number of distributions are on the market, geared particularly for multimedia production, that come with real-time priority enabled, with the distribution binaries built with all the architecture-specific and real-time optimizations turned on. Planet CCRMA (Fedora-based), DeMuDi, Ubuntu Studio and 64 Studio (all Debian-based) all come with things set up this way, and if you're building a field recorder from scratch or don't mind re-installing the operating system, they are all excellent starting points for your system. Although I have used all of them and find them all quite capable, I ultimately chose Ubuntu Studio for the sake of consistency with the rest of my platforms—I run Ubuntu flavors on most of my workstations, and even though it's well tuned for real-time use, Ubuntu Studio is more of a general-purpose distribution than is my other favorite, 64 Studio.

Hardware Configuration

Ubuntu Studio is currently in the Debian Feisty iteration, which presents a problem when working with the Multiface 2, as the Ubuntu ALSA version included doesn't contain the correct firmware to activate the hardware. To remedy this, however, a two-pronged attack is required. First off, the ALSA firmware loader, which is not installed by default, needs to be loaded—a task easily done with apt-get. Once that's done, loading the firmware still fails because of the bug in the bundled ALSA version. Heading over to alsa-project.org and downloading, building and installing the v.1.1.4 or better firmware fixes this problem neatly. Once that's done, restart the computer. So long as the rest of the default packages are installed (which include particularly all the HDSP tools), the system should recognize the interface automagically.

To test it, open the hdspmixer utility (Figure 1), plug in a microphone or instrument, and do a levels test. Keep this mixer open, as it is your primary first-level control to govern what's coming into your system.

Figure 1. hdspmixer Utility

JACK

Now that the hardware is up and running, it's time to get the software whipped into shape. Pro Audio production on Linux is handled entirely through the JACK Audio Connection Kit, which allows software to access the hardware in real time through the real-time-enabled kernel. On the studio distributions, this software is installed by default, although if you intend to use the latest-and-greatest multitrack recording software we'll examine in a moment, you need to upgrade to a later version of JACK than is currently included in Ubuntu Studio.

To start JACK from the command line, enter jackd -R -d alsa -d hw:1 (hw:1 denotes the second sound card in your system, which will almost always be correct when you're dealing with a laptop, as it has a built-in sound card). Once that's done, start up QJACKCtl or another one of the graphical patchbay clients—you'll need it (Figure 2).

Figure 2. The patchbay is used for routing sound from the hardware into the applications, from one application to another, and then back out to hardware outputs.

Ardour

When it comes to multitrack recording on Linux, one project shines above and beyond all the other audio recording software available for the platform. That project, Ardour, is maintained by Paul Davis and is unabashedly geared for professional audio engineers. Like Blender, which has a naked aim to be a free professional 3-D finishing system for the masses and is designed with professionals in mind, so too is Ardour aiming squarely for audio professionals, with an interface design borrowed from programs like ProTools and then tweaked with an eye toward improving upon it. As such, its interface is daunting and obtuse for the newbie, but it operates with great efficiency and transparency once you get acclimated (Figure 3).

Figure 3. Ardour

The version of Ardour that ships with the current studio distributions at the time of this writing is version 0.99, which lags behind the current release, now comfortably into 2.0 territory. For most purposes, 0.99 is fine, though some of the improvements in version 2.0 are ones you'll want to take advantage of eventually. If you want to get up and running in the quickest order, start the version that comes with your distro, connect the HDSP patchbay outputs to the Ardour inputs, and you're up and running (Figure 4).

Figure 4. Ardour Up and Running

If, on the other hand, you want to use Ardour 2.0, you need to do the requisite download/compile/install routine for both the new version of JACK and for Ardour, and you will not have to start JACK or QJACKCtl before starting Ardour—the new version of Ardour has a JACK control interface built in. In either case, when you're up and running to this point, you're ready to rock and roll. Plug your microphones or instruments to your breakout box, and begin recording. But, keep the manual wiki handy until you get familiar with things!

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24 channels @ 96KHz?

Josja's picture

Do you record 24 channels @ 96KHz with one HDSP II and some 'adaptor cables', costing around $600? Amazing, I really like to know how!
As an recording engineer I love your idea to swap my 24 tracks Alesis HD24 for a RME HDSP... But as the HDSP you are mentioning only has 8 line-inputs I can't figure how to connect 24 line-level signals to it. What is exactly the trick with the 'adaptor' cables?

As for the higher than 48KHz samplerate, I personally love the higher definition when it comes to recording classical, the HD24 will do that on 12 tracks with an optional AD converter, (pop/rock recordings don't benefit noticeably imho), but I don't see any reason for recording higher than 48KHz as my 'audience' (the consumer market) doesn't hear the difference and they are very happy with CD recordings @ 44.1KHz and most of them even love MP3s(!).

About that RME gear

David L's picture

Dan,

Good article, but...

I went looking for the RME Hammerfall HDSP Multiface II and it says that in order to use the break out (which only seems to support balanced 1/4" jacks rather than the standard XLR that most mics come with - is that a phantom power issue I wonder? Do you use XLR to 1/4 successfully?) I need the PCMCIA CardBus which you don't seem to mention, pushing the price of the gear closer to $1000. Did you use the Hammerfall without the cardbus? If so was it over Firewire because I don't see a USB interface on the back side of the Multiface II.

While not technically a Linux issue, it is key to making the whole thing work successfully and maybe a little more detail would make it a little more clear.

Clarification

dsawyer's picture

David -

One of the things I keep around are a collection of adapter cables, a couple batter-powered preamps and, now, a portable mixer - that deals with the problems related to the XLR inputs. But indeed, if you're needing XLR inputs right in the box, one of the Presonus interfaces is probably more up your alley than the RME.

I actually did buy the cardbus card in addition to the Multiface, only to discover that the Multiface shipped in a case with one of the cardbus cards. It wasn't as nice as the cardbus cards that sell separately, but it does the job perfectly well. So, unless I got lucky and they accidentally popped a cardbus card into the wrong box, then the multiface II really does ship with a bare-bones cardbus card. I wound up returning the Cardbus HDSP that I bought separately and buying a really nice portable Yamaha mixer with the cash back.

Since I wrote the article, I've been using it to record my podcasts at http://www.reprobateshour.com and http://sculptgod.jdsawyer.net.

Hope that helps
-Dan Sawyer

Thanks - that's a start!

kg4giy's picture

Dan,

That does help, yes. It seems that there are some package cardbus deals out there which did not seem to keep the price in line but I will take a look at the other suggestions you made since I don't keep the spares around that you do, although I do have a portable mixer that would do the trick in a pinch.

I will be working on this over the Christmas holidays and with any luck I will report out my findings for those that are following along at home.

DAVID

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