[LAU] Neophyte questions re: selecting an audio interface

[rosea.grammostola]

On 01/07/2012 01:05 AM, linux-audio-user-request at lists.linuxaudio.org wrote:
> On Fri, Jan 06, 2012 at 10:50:12AM -0500, Chris Metzler wrote:
>> >  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.
> Adapters don't normally introduce noise or degradation. But they
> are often used to connect things that are not compatible anyway,
> and they tend to fail (bad contacts) after some time. Try to avoid
> them, they are in general a nuisance.
>
> RCA inputs are 'consumer line level' and unbalanced, which is
> a disadvantage.
>
> Line inputs are not meant for guitars, so those people who
> are complaining get what they ask for.
>
>> >  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?
> Sound quality is not determined by the connector. But the use of
> such connectors can indicate 'budget quality'. Very often they are
> used as a combined mic/line input (mic = XLR, line = TRS). Then
> it depends: if the line input is just an attenuator feeding the
> mic input that's not really very good. A real line input does not
> pass via the mic preamp.
>
>> >  3. ... 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?
> No.
>
>> >  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)?
> Guitars are not line level, they produce a much weaker signal and
> need a preamplifier with a high input impedance. Some sound cards
> have 1 or 2 inputs that can be switched for use with guitars.
> Without those you need a DI box.
>
>> >  b)  Am I correct in thinking that a cable with TS connectors is
>> >  unbalanced and a cable with TRS connectors is balanced?
> A cable with TRS connectors*can*  be balanced, one with TS
> definitely is not 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?
> Any balanced input will accept balanced and unbalanced signals.
>
>> >  If an interface only has mic/line jacks, does that mean you*must*
>> >  get a DI box to plug in a guitar?
> Yes, unless the line input can be switched to high impedance and has
> enough sensitivity. As already mentioned, some interfaces have such
> inputs. But you can't use a standard mic or line input for a guitar.
>
>> >  d)  Since guitars aren't at line level, do they need preamplification
>> >  like microphones do?
> Yes. Normally the DI box is connected to a microphone input.
>
>> >  Or if an interface has unbalanced inputs, can you just plug a
>> >  guitar in and go?
> In most cases not, see above.
>
> Some other things to consider:
>
> Usually you get what you pay for. Quality is not only sound
> quality, but also construction and reliability, and it has
> a price.
>
> If you are a musician, consider the combination of a simple
> but good quality soundcard having only balanced line inputs
> and outputs (even fixed level) with one the many small
> musician's mixers. These usually have mic and guitar inputs,
> a headphone output etc. Such a combination is much more
> flexible than any soundcard.
>
>
> Ciao,
>
> -- FA

Fons, interesting view. Could you give specific examples of such 
soundcards and small musician mixers?

Regards,
Dirk