[gui-talk] Fwd: Testing inputs on the Plextalk

[Steve Pattison]

From: ptr1-users at freelists.org
On Behalf Of Frank Cuta

Testing the microphone and high level inputs on the Plextalk Recorders

Summary:

I took some time over  the holidays to make some tests with my PTR1,
PTR2 and the new PTP1 Pocket.   These tests  are not extremely
professional and certainly  not comprehensive.   I had a cheap and dirty
way of looking at input sensitivity and that is what I concentrated on.

  Mostly I wanted to put the microphone input of the Plextalk Pocket 
through
its paces  but I also wanted to compare its input
characteristics with those of the PTR1 and PTR2.   Eventually I extended
my testing to the high level input as well.

I will first discuss  what I think I learned -- Farther below I  provide 
the
details of my testing process in case you are interested.


Note that these tests are limited to the input sensitivity of the 
microphone
preamp in each unit.  This is of interest because most distortion issues 
are
related to a mismatch between the microphone and this input sensitivity.
In my listening tests I noticed  no gross differences  in frequency
response, out put drive or any of the other important sound 
characteristic
between  these 3 models and in any case I do not have the instruments
necessary to make such tests.  However, the sensitivity of the 
microphone
preamps is another story.  They are different in all 3 models.  Having a
better understanding of these sensitivity characteristics  can assist 
you to
match your microphone with your
preamp for a given situation and reduce the   possibility of you winding
up with a distorted recording.

you can see from a quick glance at the figures below that the most 
sensitive
microphone preamp is in  the PTR1, the least sensitive microphone preamp 
is
in the PTP1 Pocket and the PTR2 is somewhere in
between.  I want to stress that   overall sensitivity is not a good
indication of quality nor is it even an indication of functionality.
For example the Sennheiser microphone on the list below   turned out  to
be the least sensitive of all microphones tested but  cost $1000 a pair
and they are  worth it.   But, on the other hand I would not choose this
microphone to go out and try and pick up bird song or other faint nature
sounds.  You have to think about  the sound levels that you typically 
deal
with and then choose how to best pick it up.  Knowing your sensitivity
characteristics can assist you to optimize your performance.
Say you are recording a meeting and have the choice to use either your
PTR1 or your Pocket and no external microphone is available.  Your best
choice would be the PTR1.  However if  a tiny single point direct plug 
in
microphone is available the Pocket would be the best choice since the 
single
point microphone will provide better pickup but it is not supported on 
the
PTR1.  On the other hand if you are using this same single point 
microphone
and singing or playing an instrument directly into it and your choice is 
to
use either a PT Pocket  or a PTR2 you would use the pocket because at 
these
levels the microphone input on a
PTR2  would be driven into  distortion.  Always keep functionality in 
mind.
Note that in my tests although the PT Pocket has the lowest input
sensitivity it is the only one of the three models that made good 
recordings
using every microphone that I tested.  Note also that since the Pocket 
is
the only one of the 3 recorders that permits you to defeat the automatic
recording level when using the internal microphone I was able to list 
its
internal microphone on the list with the other microphones that I 
tested.


I  made excellent recordings on all 3 units using their high level
inputs.  I made tests with 4 Sources,   the high level outputs  from my
sony CD player, a Yamaha EMX200 mixer, a $50 pocket sized Archos 
microphone
preamp and a $180 pocket sized Sound  professionals microphone preamp. 
The
tests with the 2 battery powered preamps turned out to be more of a test 
of
the preamps than the Plextalks.  The Archos gets all of its gain in the
sweep of a single pot and is very  touchy.
The Sound  Professionals unit has discernibly less internal noise and is
more controllable since it achieves  its gain in 3 separate ranges.
Both preamps functioned perfectly  with all of the professional 
microphones
on my list but when using the very hot single point microphones and my
fairly loud test signal it was easy to drive the Plextalks into 
distortion.
I believe these preamps were originally designed more for interfacing
professional microphones with high level inputs on  portable recorders.

Last, I Attempted an ultimate gain arrangement by using a very hot 
single
point microphone to drive the Sound  Professionals preamp and feeding 
the
output of the preamp into the microphone input of the PT Pocket.  This
actually works very well but do not try it unless you are in a very very
quiet environment.  I attribute the success of this test to the very low
noise spec on this fine preamp.  With this system I am recording sounds
inside and outside of my home that I cannot hear with my normal hearing.
Warning do not try this if there is any danger of being interrupted by a
ringing telephone or some one talking to you from a few feet away.  The
result could damage your ear drums.


Testing Details:

I have a  collection of microphones at my disposal of various 
technologies
and with a corresponding wide range of sensitivity values.
A microphone's sensitivity   spec  determines how hot of an output
signal you get for a given input level.  My goal was to make tests with 
a
selection of these microphones and make lists  of the respective manual
recording settings that it takes to achieve a "good" level on each model 
of
Plextalk.  The assumption is that given the fixed sensitivities of the
respective microphones and the constant level of the sound source if I
tested each microphone with each Plextalk I will have a basis for 
comparing
their  relative input sensitivities.

I picked a high  quality sound source of a specific level and played the
same material  over and over on it while I changed machines, microphones
and adjusted  manual recording levels.   The material was  a live Robin
and Linda Williams concert that I  recorded as a wave file off of my 
Mackie
1640 soundboard.  I played back the CD through my studio monitors and 
set up
each pair of microphones 36 inches  from the monitors.  The sound 
pressure
level  meter read 96 dB max  at the microphone grilles and was never
changed.  The microphones were connected directly to the microphone 
input of
each Plextalk with a single  unit Y cable which
accepts 2 XLR microphone outputs and converts them to a stereo   3.5 mm
phone connector -- no noisy adapters.  (I believe that the cable is made 
by
Hosa.)  For each test I connected a pair of microphones and kept turning
down the recording level on the recorder until it said good.
The professional microphones ranging in sensitivity from lowest to 
highest
were Sennheiser 441, Electro Voice RE-15, Shure sm58, Shure beta 58, AKG
c1000 and Audio Technica ATM31.  The first 4 are dynamics and the last 2 
are
condensers.  This was going to be the extent of my testing but at the 
last I
added to single point stereo electret microphones, one from IRTI and one
from Sound Professionals.  I was surprised to learn that  they are 
actually
much hotter  than even my most expensive professional microphones.

For each test I started with the audible  level reading high and kept
turning down the manual recording level until it said good.  The value
recorded in the list below is  thus the approximate max recording level 
that
could be set on that recorder for a specific microphone with an input 
level
of 96 dB. .


Plextalk Pocket:

441= 15
RE15 = 14
SM58 = 14
Beta SM58 = 13
C1000 = 10
ATM31 = 9
PTP internal = 9
T single point (from SP) = 6
Single point (from IRTI) = 6

Plextalk PTR2:
441 = 13
RE15 = 12
SM58 = 12
Beta SM58 = 11
C1000 = 7
ATM31 = 6
Single point (from IRTI) = 5 (audible overdrive distortion at this SPL) 
T
single point )from SP) = 4 (pronounced overdrive distortion at this
SPL)

Plextalk PTR1:

441 = 11
Re15 = 11
Sm58 = 11
Beta sm58 = 9
C1000 = 6
Atm31 = 6
(single point electret microphones not supported)

I then sat down and listened to the results on studio monitors and 
several
different headphones.

Regards Steve
Email:  srp at internode.on.net
Windows Live Messenger:  internetuser383 at hotmail.com
Skype:  steve1963