Re: [LAU] Neophyte questions re: selecting an audio interface

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To: <linux-audio-user@...>
Date: Friday, January 6, 2012 - 4:42 pm

On Fri, 6 Jan 2012 10:50:12 -0500
Chris Metzler wrote:

This is very nice. I'd add that Firewire can be problematic under Linux
depending on the chip used to implement it.

> - -Questions I have-

It can happen with just about any cheap cable or adapter. That said, I'd
rather have an interface with 1/4" balanced connectors, which is why I
went for the full M-Audio Delta 1010.

> 2. Some interfaces seem to have a combination jack that allows XLR and

I've used these on a few preamps now, including an ART and M-Audio's
Studio I/O, and have never had a problem. I like the convenience of them!

> 3. if you have the chance to pick up at a

None that I can think of. I started small and kept upgrading as it
turned out I'd use more and more I/O ports on a project. I use 2
1010's now (16 I/O ports total) and other than occasionally running short
on preamps (I only have 9 channels of preamp available, the 1010 has no
preamps) it's been enough.

> 4. I'm so confused about what I can plug into an interface's 1/4" jack

Guitar signals are actually pretty weak, and need some sort of preamp
before they're really usable. This can often be done in software, though;
packages like Guitarix (http://guitarix.sourceforge.net/) will help create
good sounds, but I always prefer micing an amp or at the very least adding
a pre-amp before taking the signal in. I record electric bass this way a
lot, but electric guitars generally sound poor without more processing,
which I like using the amp for. Again, Guitarix will simulate an amp here,
or external units like the Line6 Pod can also provide this processing
(as well as giving you a line-level signal).

Balanced vs. unbalanced (or TRS vs. TS) has nothing to do with line
level, though. That has to do with the signal strength. Professional
audio gear considers line level to be +4 dBu (~1.228V RMS) while
consumer audio uses -10dBu (~0.316V RMS). Guitar pickups and mics
are typically much lower than that - anywhere from 1 - 300 mV if I remember
correctly.

> b) Am I correct in thinking that a cable with TS connectors is

Yes. Also, mic connectors (XLR) are balanced.

> c) My understanding is that in order to plug a guitar into a balanced

This is true, but not so much to change the impedance, but to introduce
it into the system. The Wikipedia entry on balanced audio gives a good
explanation of the details. In short, you introduce balanced impedence
to reduce audio interference. The DI may be passive or active, which
indicates whether a preamp is in the circuit. No preamp = passive.

> But in advertising blurbs, some 1/4" inputs on interfaces are billed as

No, it means that you can use either type of cable (TS or TRS) and
make a connection. It's got nothing to do with line level. If you
have unbalanced connectors, you can use a TRS cable but you won't get
any of the benefits of balancing. You can use a TR cable with balanced
connectors, but again lose the actual balancing - most of the time. You
might occasionally run into balanced connectors that won't want to work
with TS cables but that seems pretty rare. Of course, both ends must be
balanced and a TRS cable used to take advantage of balancing.

> If an

No, but the signal may be prone to interference if you don't.

> d) Since guitars aren't at line level, do they need preamplification

Yes, but this is often doable in software. This is why you can't get a
1/4" to RCA connector and just plug a guitar into the tape inputs of a
home stereo and get anything resembling a good sound out, the signal's too
weak for the main amp to do much with it.

> Or if an interface has unbalanced inputs, can you

Nope, again it's got nothing to do with impedance or balancing or the
type of input, and everything to do with signal level.

Hope this helps!

--
======================================================================
Joe Hartley - UNIX/network Consultant - jh@brainiac.com
Without deviation from the norm, "progress" is not possible. - FZappa
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Messages in current thread:
Re: [LAU] Neophyte questions re: selecting an audio interface, Joe Hartley, (Fri Jan 6, 4:42 pm)
Re: [LAU] Neophyte questions re: selecting an audio interface, Ricardus Vincente, (Sun Jan 8, 1:01 am)