I'm confused. I thought all XLR mics were low-Z,
but now I'm not sure. Is 1000 ohms low-Z or
high-Z ??? Thanks.
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>From Tue Mar 8 18:27:45 2005
Message: 5
Date: Fri, 20 Aug 2004 21:38:15 -0000
From: "Rich Peet" <>
Subject: Re: Minidisc Mic Input
Knowing that Adam has a lot more experience with a lot better
equipment than I do I made sure to do my homework before I posted
this.
For the high end recorders that Adam is use to, or for manufactured
products for universal use, I agree with his statements. But for
consumer minidisc use alone, I do not.
My tests I did today were conducted on a standard Sony Consumer
minidisc mz-r55 transfered to a computer by analog line out to a good
a/d converter and analyzed within Adobe Audition. The microphone was
a Sennheiser ME-62.
I favor a 1 uf tantalum on the line to cut subsonic noise and think
that 27uf is too high for consumer minidisc recorders. Recording one
channel straight in and the second through a 1 uf tantalum capacitor
showed no drop in gain above 90hz and less than 3 db above 35hz. The
channel with the capacitor had less compression above 14,000 cycles.
Consumer minidisc recorders favor low frequency sound no matter how
low it is and therefore it is better to get rid of some non audible
subsonic rumble.
Next a 10,000 ohm 1/4 watt metal film resister was placed on one
channel and the other straight through. The capacitor was removed.
The drop in gain was 10 db below 10,000 cycles. Above 10,000 cycles,
which in this test was very quiet, there was less of a drop due to
less atrac compression.
No additional noise could be detected anywhere on the channel with
the 10,000 ohm resister at any frequency.
So overall Adam is correct, but my prior post is preferred for
consumer minidisc use.
Rich
--- In "Adam Liberman" <>
wrote:
> We use the Panasonic FC 27uF/25v cap in the Minidisc mic cables
that
> we sell. It is Digikey P11214 and it fits nicely inside the XLR
> connector.
>
> The FC series replaced the HFS series, and is regarded as a good
> audio cap - low dissipation factor and long life. The measured roll-
> off with a 200 ohm source impedance into a Sharp MD-DR7-A MiniDisc
> recorder is only 0.3dB at 20Hz. You won't find any poly cap that
> will fit inside the XLR connector and not have excessive roll-off.
>
> As far as the resistor, the value would depend on the input
> impedance of your MiniDisc. But any value will add noise, and some
> MiniDisc mic pre's are already not as quite as they should be, so I
> wouldn't use the resistor. Putting the same signal on both channels
> may be redundant, but redundancy can be a good thing as far as
> reliability is concerned, and it will also mean that both ears in
> your headphones will have an equal signal level which is more
> natural for monitoring.
>
> Thanks,
> Adam Liberman
> Liberman Sound
>
> --- In "Dave J" <>
> wrote:
> > That may be a good idea to have an attenuated channel
> > just in case I ever have a clipping problem. I thought
> > 100uF was rather huge but that is what they show in the
> > AKG booklet. Maybe because it is a low-z mic? Probably
> > of no concern unless I record bullfrogs. I will look in
> > Digikey for poly caps.
> >
> > --- "Rich Peet" <> wrote:
> > > 100 uf would be to big, 2uf in a quality cap would be
> > > better. I use tantalum but poly would be best. I recall
> > > the cap as really not needed if you short the channels.
> > > You may wish to try a metal film resister on one channel
> > > so that you have high and low gain channel to choose
> > > from. I would guess that 5,000 to 10,000 ohms would be
> > > about right but that is a educated guess right now.
> > >
> > > Rich
> > >
> > > --- "Dave J" <> wrote:
> > > > Am I correct that for mono microphones I can simply
> > > > short the L & R minidisc mic channels together? I'm
> > > > not inclined to do true mono recording so I'll just
> > > > waste disc space with bogus stereo. I realize there
> > > > is 2.5VDC on both of them so once I short them I'll
> > > > use a 100uF coupling capacitor to get the signal in.
> > > >
> > > > Thanks,
> > > >
> > > > Dave
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"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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