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Portable Hard Disk Recorder How-To

Issue 164

From Issue #164
December 2007

Dec 01, 2007  By Dan Sawyer
 in
Use an old laptop to build a multitrack hard disk recorder.
Final Thoughts

Three years ago, this project would have been a royal pain in the hind end. Although the Multiface has always been Linux-compatible, once upon a time, doing real-time audio on any hardware required a lot of fancy command-line tricks and kernel recompilation. The plethora of studio distributions in the last couple years has radically changed the process and has brought the most powerful parts of the Linux multimedia subsystem into the reach of people who are power users and hobbyists, rather than remaining in the domain of kernel hackers. Thanks to the power of Linux and open-source software, for the cost of an old laptop and a new audio interface, you own a proper, full-featured, multitrack digital audio field recorder. Go forth, record, edit, create and compress!

Some Problems with Digital Audio

As you go about your recording, you're going to discover some of the limits of digital recording, such as the fact that current technology doesn't allow for sample rates high enough to reproduce cymbals and other sounds with high, clear treble accurately—sounds you won't run into when recording voices, but you will encounter in music and sound effects. To better understand how digital sampling works, and how you can use sound reinforcement and acoustic techniques to overcome some of those limitations, pick up the Yamaha Sound Reinforcement Handbook. It will help you understand how audio reinforcement works and how to compensate for such problems.

Resources

Laptop-compatible Pro Audio interface support is spotty and hard to find accurate information on, but an excellent place to start is the FFADO Project at www.ffado.org.

The other place for good information is the ALSA Project hardware database at www.alsa-project.org.

For more information about tweaking the RME Multiface 2, see the HDSP How-To at pd.klingt.org/files/hdsp-howto.html.

Dan Sawyer is the founder of ArtisticWhispers Productions (www.artisticwhispers.com), a small audio/video studio in the San Francisco Bay Area. He has been an enthusiastic advocate for free and open-source software since the late 1990s, when he founded the Blenderwars filmmaking community (www.blenderwars.com). Current projects include the independent SF feature Hunting Kestral and The Sophia Project, a fine-art photography book centering on strong women in myth.

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24 channels @ 96KHz?

Josja's picture
Submitted by Josja (not verified) on Mon, 08/04/2008 - 13:11.

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
Submitted by David L (not verified) on Tue, 11/13/2007 - 07:37.

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
Submitted by dsawyer on Thu, 11/22/2007 - 02:50.

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
Submitted by kg4giy on Thu, 11/29/2007 - 14:37.

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

David A. Lane is a Linux Journal Reader Advisory Panelist.

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