[LAU] [Music] For fun 1 and 2

[Len Ovens]

On Sat, 2 Jul 2016, jonetsu at teksavvy.com wrote:

>> The ATs are ok (I have an AT2020) placement matters and pre. I have
>> tried both first gen discrete Mackie CR pres and an ART tube pre.
>> (wish I had nicer) The ART is more up front perhaps because of the
>> limiter inside. I also use a couple NT450 dynamic larger diapham mics
>> which sound a little flatter than sm58 do. But nothing fancy.
>
> As of now the mics are connected directly to the m-audio 1010LT card's
> 2 XLR jacks (through a phantom power box for each).  In which way would
> a preamp affect the sound ?

the preamp can affect the sound in any number of ways. The most noticable 
thing I have seen with cheaper preamps has been noise floor. Put the 
nominal resistance in place of the mic, set the alsa level for the adc to 
0 (or maybe plus 18) and use a meter application (meterbridge works) look 
at the level. The 1010LT has 144DB dynamic range in theory (24 bits), but 
a good preamp is more likely around 110 (noise at -110dbfs). The LT is 
likely not that good. These are with the needed gain thrown in to bring 
the gain up to whatever the ADC is using (probably less than a line level 
of +4 because the audio PS is only 12v so far as I know) I have two ART 
pre, the USB Dual Pre.... ok for condenser mics, but the last 5 degrees of 
gain control sure adds a lot of hiss. They say 48db of clean gain... it 
doesn't seem to be quite enough for a dynamic mic unless the audio is 
quite loud to begin with. I also have the USBDualTubePre which claims 65db 
gain. It is noticably quieter for sure. The mackie CR1604 just works, I 
have never noticed hiss in that and no colouring, almost sterile.

Preamps can also have (or not) a nonlinear transfer character where the 
positive going half may be amplified differently that the negative or the 
peaks may be amplified different from the signal close to the zero 
crossing point (one hopes not actual crossover distortion).

Frequency response is another place some preamps are better than others or 
may sound more pleasing (some times pleasing comes from a non-linear 
frequency response).

Though not likely to affect the AT2050 which has a builtin preamp already, 
many types of preamp may not have an input impedance well suited to the 
mic. Dynamic mics are pretty forgiving (SM58s etc), but ribbon mics, raw 
piezo pickups or crystal mics just sound better if the preamp input is 
matched correctly. The mackie cr1604 for example, does not sound very good 
with my piezo pickup either on the mandolin or my acoustic guitar, but 
both sound quite good going through a Fishman pre. (I have an Fishman amp 
I sometimes use as a pre as it has line out) I regret to report I do not 
have a ribon mic at this point (they sound more like an unmiced source 
even with less than perfect frequency responce of only up to 15k or so) so 
I haven't tried one of those.

I have a delta66 which is sort of in between the delta 1010 and the 
1010LT. The deltas have only line level (+4 or -10) with the LT being the 
one that has the mic pre for two inputs. Considering everything else they 
have stuffed into the LT I would have to question the quality of preamp. 
It is not hard to find a mic pre for 3k or more. Hand built ones include 
the idea of hand picking matched transistor pairs for each stage, 
transformer inputs or outputs are common too. (some audio transformers may 
cost as much as the LT...)

> There are many good reviews about the ART MP preamp (although MPA II

Mine is probably not that good though it sounds good to me. I get 24 
bit adc out mine by taking s/pdif out and into the delta66.

> would be more like it), the price is OK. One reviewer mentions that the
> interface level should be set to neutral gain.  Looking at the 1010LT
> manual, the interface has hardware DIP switches that offers two choices
> for the mic inputs:
>
> 1) +30dB gain
>
> 2) Attenuates +30dB by 11dB (i.e., +19dB gain)
>
> Te mudita24 panel currently has the gain set at 0 dB for both XLR
> inputs.  What is the role of the DIP switches - does it mean that there
> is no possibility of having neutral gain at all since the hardware
> choices are +30dB or +19dB ?

My version of mudita24 shows the adc full up position at +18.5 so with the 
jumper set to the lower gain position, setting mudita to 0db should be 
right. Check for digital clipping though and modify the setting of the pre 
and/or mudita to make sure there is never digital clipping.

+30db gain overall is not really enough for dynamic mics, preamp required.

> The acoustic guitar I use has an interesting 'challenge' in recording as
> far as there is no hole.  Like the one at the bottom of the page,
> only acoustic only:
>
> https://www.guitarscanada.com/index.php?threads/shiraki-anyone.507/
>
> This actually might do away with the booming issue of having a mic too
> close to the sound hole on a regular guitar.  On the other hand it also
> disperses the sound.

The sound hole is there, just not under the strings. If the mic is 12 to 
18 inches away (if your room is quiet enough :) it should pick up the 
sound pretty well. I don't know how the "grill" affects the sound, nor how 
the spreading of the sound hole over so much of the sound board affects 
things either. You have one so you can listen to it :)


--
Len Ovens
www.ovenwerks.net