[LAU] Neophyte questions re: selecting an audio interface

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To: <linux-audio-user@...>
Date: Friday, January 6, 2012 - 3:47 pm

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Hi. After a much longer delay than I wanted, I'm finally getting the
chance to get into recording. Right now I only have consumer audio
line-in capability and need to get a better interface. To help
decide what to get, I've been reading old posts on this mailing list
and have come up with what seem to me to be the pros/cons of PCI, USB,
and FireWire interfaces. I'm hoping that folks having more of a clue
than I do will look at this list below and tell me if what I've
concluded is right/wrong, as well as any pros/cons I may have missed.
At the end, I've tacked on some additional questions that have come up
while reading. I really, really appreciate any advice you can give.

- -Pros/Cons of Interfaces-

- ---
- - Low latency
- - High data rates -- can handle lots of inputs/outputs at high sample

- - Outdated technology -- PCI slots being slowly phased out of modern
- - Interface not portable -- can't use it with a laptop
- - Latency tuning possibly required (identifying IRQs associated with
PCI slots and picking slot accordingly)
- - Computer-caused interference noise possible unless audio converted to
digital domain outside computer ==> breakout box. But PCI interfaces
with breakout boxes tend to be pretty expensive. OTOH, no breakout
box = lots of cables going to the back of the computer.

- ---
- - Interface portability -- everything has a USB port these days
- - Current technology
- - Relatively cheap
- - Outside computer ==> less electrical interference noise

- - USB 1.1 devices are generally well-supported; but USB 2
devices probably aren't.
- - USB 1.1 limitation means serious sample rate/channel # limitation. A
single 24/96 channel means 2.3Mbps; 12Mbps nondirectional hard limit
under USB 1.1 so only 2 channels full duplex, or 4-5 inputs/no
outputs, possible.

- ----
- - High data rates
- - Outside computer ==> less electrical interference noise
- - Portable; no fiddling with internal cards.
- - More options supported at high data rates than USB.

- - Long-term viability of 1394 interface? Will my next computer have
one? Will a future laptop?


- -Questions I have-

1. Some PCI interfaces (like the Delta 1010LT) have RCA jacks rather
than 1/4". What about issues relating to noise/degradation introduced
by a 1/4"-to-RCA adapter? I've read elsewhere (on the M-Audio forums)
of people complaining about unpleasant noise with guitars when using an
adapter that's then plugged into an RCA plug on the Delta 1010LT.

2. Some interfaces seem to have a combination jack that allows XLR and
1/4" inputs. Are these good? Or is there a tradeoff between
convenience and sound quality?

3. When selecting an interface, I don't want to just look at what I
need right now, because I don't want to replace my interface every 1-3
years. But I sometimes see people selling audio interfaces with the
explanation that what their selling is "more than they need." Maybe
they're just recovering some money; but are there reasons (other than
cost) one *shouldn't* pick up an interface with a lot of excess
capability? Put another way, if you have the chance to pick up at a
really good price Z-Audio's UberSuperDuperInterface, with a gazillion
ins/outs and a lot of features, and right now you only need a small
fraction of what it can do, are there non-cost reasons why you
*shouldn't* get it?

4. I'm so confused about what I can plug into an interface's 1/4" jack
at this point that I'm having trouble even articulating questions.
Here's my best shot:

a) Guitar cables typically use a TS connector while line-level devices
(analog outs on drum machines, keyboards, etc.) typically use TRS,
right? I'm presuming there's a difference in voltage range as well
(hence why guitars aren't referred to as line-level)?

b) Am I correct in thinking that a cable with TS connectors is
unbalanced and a cable with TRS connectors is balanced?

c) My understanding is that in order to plug a guitar into a balanced
input, there needs to be a DI box in-between to change the impedance.
But in advertising blurbs, some 1/4" inputs on interfaces are billed as
accepting balanced or unbalanced input. Does that mean that both
guitars and line-level devices can be plugged into them? If an
interface only has mic/line jacks, does that mean you *must* get a DI
box to plug in a guitar?

d) Since guitars aren't at line level, do they need preamplification
like microphones do? Or if an interface has unbalanced inputs, can you
just plug a guitar in and go?


Thanks much for any and all help!

- -c

- --
Chris Metzler cmetzler@speakeasy.snip-me.net
(remove "snip-me." to email)

"As a child I understood how to give; I have forgotten this grace since
I have become civilized." - Chief Luther Standing Bear
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Messages in current thread:
[LAU] Neophyte questions re: selecting an audio interface, Chris Metzler, (Fri Jan 6, 3:47 pm)
Re: [LAU] Neophyte questions re: selecting an audio interface, Ricardus Vincente, (Sun Jan 8, 1:01 am)