| Author |
Message |
Andy & Kim
Guest
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 Posted:
Fri Oct 07, 2005 12:42 am Post subject:
Line into mic input |
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Hi guy's what would I need to put a line level input into a mic input of my
little had held digital camera. Would it just have to be a potential divider
or would it require some EQ.
Andy
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Smarty
Guest
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| Posted:
Fri Oct 07, 2005 1:28 am Post subject:
Re: Line into mic input |
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You will not need equalization, but you do need to attenuate the line level
signal (nominally about 1 millivolt into 47K ohms) down to a few microvolts
(also at the same impedance). Thus an attenuator / pad of about 30 dB should
do it.
Smarty
"Andy & Kim" <Andy@akmt.demon.co.uk> wrote in message
news:di3und$db1$1$8300dec7@news.demon.co.uk...
| Quote: | Hi guy's what would I need to put a line level input into a mic input of
my little had held digital camera. Would it just have to be a potential
divider or would it require some EQ.
Andy
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Larry J.
Guest
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| Posted:
Fri Oct 07, 2005 1:44 am Post subject:
Re: Line into mic input |
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Waiving the right to remain silent, "Smarty" <nobody@nobody.com>
said:
| Quote: | You will not need equalization, but you do need to attenuate the
line level signal (nominally about 1 millivolt into 47K ohms)
down to a few microvolts (also at the same impedance). Thus an
attenuator / pad of about 30 dB should do it.
|
An even larger pad could be required. Unbalanced live levels are
generally -10 to -20db. Balanced can be as high as +8.
--
Larry Jandro
Video Engineering & Equipment Rentals
Scottsdale, Arizona, USA
[Remove spamtrap in ALLCAPS to reply] |
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Smarty
Guest
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| Posted:
Fri Oct 07, 2005 2:22 am Post subject:
Re: Line into mic input |
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Most if not all of the camcorders do AGC on the audio inputs, and have at
least 60 to 80 dB of dynamic range. Virtually all the camcorders use
unbalanced inputs. I have build T-pad attenuators with a simple 3-resistor
T-network to do precisely what the original post asked for, and the
attenuators which do around 30 or so dB seem to work just fine. Putting in
too much attenuation forces the AGC to "gain-up" and crushes the SNR by
raising the noise floor.
Smarty
"Larry J." <usenet2@DE.LETE.THISljvideo.com> wrote in message
news:Xns96E78BC2755B6thefrogprince@68.6.19.6...
| Quote: | Waiving the right to remain silent, "Smarty" <nobody@nobody.com
said:
You will not need equalization, but you do need to attenuate the
line level signal (nominally about 1 millivolt into 47K ohms)
down to a few microvolts (also at the same impedance). Thus an
attenuator / pad of about 30 dB should do it.
An even larger pad could be required. Unbalanced live levels are
generally -10 to -20db. Balanced can be as high as +8.
--
Larry Jandro
Video Engineering & Equipment Rentals
Scottsdale, Arizona, USA
[Remove spamtrap in ALLCAPS to reply] |
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Steve King
Guest
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| Posted:
Fri Oct 07, 2005 2:47 am Post subject:
Re: Line into mic input |
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"Smarty" <nobody@nobody.com> wrote in message
news:iv-dnTLi_8s_CNjenZ2dnUVZ_sidnZ2d@adelphia.com...
| Quote: | Most if not all of the camcorders do AGC on the audio inputs, and have at
least 60 to 80 dB of dynamic range. Virtually all the camcorders use
unbalanced inputs. I have build T-pad attenuators with a simple
3-resistor T-network to do precisely what the original post asked for, and
the attenuators which do around 30 or so dB seem to work just fine.
Putting in too much attenuation forces the AGC to "gain-up" and crushes
the SNR by raising the noise floor.
Smarty
I have found that Jay Rose is right on, when his tests pointed to an input |
signal of -30 db as a sweet spot for VX2000/PD150 type cameras. If I recall
correctly, his test set-up was +4 db out of a balanced mixer with a 35 db
attenuator following.
Steve King |
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Smarty
Guest
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| Posted:
Fri Oct 07, 2005 12:16 pm Post subject:
Re: Line into mic input |
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Steve,
The original post specifically asked about "a little hand held digital
camera", not the PD150 camera style with low impedance balanced inputs, and
switchable AGC. I don't disagree with your solution for a balanced output,
since 5 dB of 'disagreement' in our opinions is well within the nominal
range of line level inputs which the original poster is likely to encounter.
The unbalanced input of a typical consumer camcorder is, however,
considerably more susceptible to hum and noise than the balanced XLR inputs
of the pro and some prosumer camcorders, and moreover has (almost always) a
non-defeatable AGC. Thus, a bit less attenuation, and putting a bit higher
signal into this high impedance unbalanced input will result in better
signal to noise performance than driving it with a smaller signal and thus
relying on the AGC to a greater extent to bring up the gain. It is a
trade-off of distortion for SNR, and the specific camcorder's
characteristics should really be accounted for, particularly its' AGC, since
those simple AGC circuits which tend to overshoot or pump or "breathe" can
and will sometimes add more objectionable effects than the hiss and hum and
other background noise which arise when a weaker (more highly attenuated) is
used.
Smarty
"Steve King" <steveSPAMBLOCK@stevekingSPAMBLOCK.net> wrote in message
news:7sGdnSmB0rMeBtjeRVn-pw@comcast.com...
| Quote: | "Smarty" <nobody@nobody.com> wrote in message
news:iv-dnTLi_8s_CNjenZ2dnUVZ_sidnZ2d@adelphia.com...
Most if not all of the camcorders do AGC on the audio inputs, and have at
least 60 to 80 dB of dynamic range. Virtually all the camcorders use
unbalanced inputs. I have build T-pad attenuators with a simple
3-resistor T-network to do precisely what the original post asked for,
and the attenuators which do around 30 or so dB seem to work just fine.
Putting in too much attenuation forces the AGC to "gain-up" and crushes
the SNR by raising the noise floor.
Smarty
I have found that Jay Rose is right on, when his tests pointed to an input
signal of -30 db as a sweet spot for VX2000/PD150 type cameras. If I
recall correctly, his test set-up was +4 db out of a balanced mixer with a
35 db attenuator following.
Steve King
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blackburst@aol.com
Guest
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| Posted:
Fri Oct 07, 2005 7:48 pm Post subject:
Re: Line into mic input |
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Andy & Kim wrote:
| Quote: | Hi guy's what would I need to put a line level input into a mic input of my
little had held digital camera. Would it just have to be a potential divider
or would it require some EQ.
Andy
|
Here's a quick and dirty soultion: Beg, borrow or steal a small
mic/line audio mixer. Connect a source like a CD player to one of the
line inputs. Feed the line out of the mixer into your camcorder. Try
different audio levels, listening through headphones or just playing
back the tape, until you find a level with no distortion and minimum
noise. Also, try to find a level that does not cause a lot of
"squashing" of the signal by the AGC. |
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Andy & Kim
Guest
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| Posted:
Fri Oct 07, 2005 7:52 pm Post subject:
Re: Line into mic input |
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"Smarty" <nobody@nobody.com> wrote in message
news:iv-dnTLi_8s_CNjenZ2dnUVZ_sidnZ2d@adelphia.com...
| Quote: | Most if not all of the camcorders do AGC on the audio inputs, and have at
least 60 to 80 dB of dynamic range. Virtually all the camcorders use
unbalanced inputs. I have build T-pad attenuators with a simple
3-resistor T-network to do precisely what the original post asked for, and
the attenuators which do around 30 or so dB seem to work just fine.
Putting in too much attenuation forces the AGC to "gain-up" and crushes
the SNR by raising the noise floor.
Smarty
"Larry J." <usenet2@DE.LETE.THISljvideo.com> wrote in message
news:Xns96E78BC2755B6thefrogprince@68.6.19.6...
Waiving the right to remain silent, "Smarty" <nobody@nobody.com
said:
You will not need equalization, but you do need to attenuate the
line level signal (nominally about 1 millivolt into 47K ohms)
down to a few microvolts (also at the same impedance). Thus an
attenuator / pad of about 30 dB should do it.
An even larger pad could be required. Unbalanced live levels are
generally -10 to -20db. Balanced can be as high as +8.
--
Larry Jandro
Video Engineering & Equipment Rentals
Scottsdale, Arizona, USA
[Remove spamtrap in ALLCAPS to reply]
Thanks for the advise guy's. Smarty could you give me some values of the |
resistors I would need for a T-pad attenuator, just as a guide.
Andy |
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Rick Merrill
Guest
|
| Posted:
Fri Oct 07, 2005 8:23 pm Post subject:
Re: Line into mic input |
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|
Smarty wrote:
| Quote: | Most if not all of the camcorders do AGC on the audio inputs, and have at
least 60 to 80 dB of dynamic range. Virtually all the camcorders use
unbalanced inputs. I have build T-pad attenuators with a simple 3-resistor
T-network to do precisely what the original post asked for, and the
attenuators which do around 30 or so dB seem to work just fine. Putting in
too much attenuation forces the AGC to "gain-up" and crushes the SNR by
raising the noise floor.
Smarty
"Larry J." <usenet2@DE.LETE.THISljvideo.com> wrote in message
news:Xns96E78BC2755B6thefrogprince@68.6.19.6...
Waiving the right to remain silent, "Smarty" <nobody@nobody.com
said:
You will not need equalization, but you do need to attenuate the
line level signal (nominally about 1 millivolt into 47K ohms)
down to a few microvolts (also at the same impedance). Thus an
attenuator / pad of about 30 dB should do it.
An even larger pad could be required. Unbalanced live levels are
generally -10 to -20db. Balanced can be as high as +8.
--
Larry Jandro
Video Engineering & Equipment Rentals
Scottsdale, Arizona, USA
[Remove spamtrap in ALLCAPS to reply]
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Rick Merrill
Guest
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| Posted:
Fri Oct 07, 2005 8:26 pm Post subject:
Re: Line into mic input |
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Andy & Kim wrote:
| Quote: | "Smarty" <nobody@nobody.com> wrote in message
news:iv-dnTLi_8s_CNjenZ2dnUVZ_sidnZ2d@adelphia.com...
Most if not all of the camcorders do AGC on the audio inputs, and have at
least 60 to 80 dB of dynamic range. Virtually all the camcorders use
unbalanced inputs. I have build T-pad attenuators with a simple
3-resistor T-network to do precisely what the original post asked for, and
the attenuators which do around 30 or so dB seem to work just fine.
Putting in too much attenuation forces the AGC to "gain-up" and crushes
the SNR by raising the noise floor.
Smarty
"Larry J." <usenet2@DE.LETE.THISljvideo.com> wrote in message
news:Xns96E78BC2755B6thefrogprince@68.6.19.6...
Waiving the right to remain silent, "Smarty" <nobody@nobody.com
said:
You will not need equalization, but you do need to attenuate the
line level signal (nominally about 1 millivolt into 47K ohms)
down to a few microvolts (also at the same impedance). Thus an
attenuator / pad of about 30 dB should do it.
An even larger pad could be required. Unbalanced live levels are
generally -10 to -20db. Balanced can be as high as +8.
--
Larry Jandro
Video Engineering & Equipment Rentals
Scottsdale, Arizona, USA
[Remove spamtrap in ALLCAPS to reply]
Thanks for the advise guy's. Smarty could you give me some values of the
resistors I would need for a T-pad attenuator, just as a guide.
Andy
|
I second the request! |
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Richard Crowley
Guest
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| Posted:
Fri Oct 07, 2005 9:57 pm Post subject:
Re: Line into mic input |
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"Rick Merrill" wrote ...
| Quote: | Andy & Kim wrote:
Thanks for the advise guy's. Smarty could you give me some values of the
resistors I would need for a T-pad attenuator, just as a guide.
I second the request!
|
http://www.uneeda-audio.com/pads/ |
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Bob Ford
Guest
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| Posted:
Fri Oct 07, 2005 10:26 pm Post subject:
Re: Line into mic input |
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On 7 Oct 2005 07:48:44 -0700, "blackburst@aol.com"
<blackburst@aol.com> wrote:
| Quote: |
Andy & Kim wrote:
Hi guy's what would I need to put a line level input into a mic input of my
little had held digital camera. Would it just have to be a potential divider
or would it require some EQ.
Andy
Here's a quick and dirty soultion: Beg, borrow or steal a small
mic/line audio mixer. Connect a source like a CD player to one of the
line inputs. Feed the line out of the mixer into your camcorder. Try
different audio levels, listening through headphones or just playing
back the tape, until you find a level with no distortion and minimum
noise. Also, try to find a level that does not cause a lot of
"squashing" of the signal by the AGC.
|
At one time Radio Shack sold a mini male to RCA that would pad a line
to mic signal. The also had a cable with same connection that was
about 3ft. long. I don't know if they still sell these or not but I
have about 2 of each in my parts box and I never use them.
If you can't find them, let me know and I can send you one for a very
minimal fee - mostly just enough to cover shipping charges.
Bob Ford
Images In Motion
www.imagesinmotion.com |
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Smarty
Guest
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| Posted:
Fri Oct 07, 2005 11:06 pm Post subject:
Re: Line into mic input |
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Glad to assist. I need to know 3 things before designing an attenuator pad.
1). Where is the Line Output coming from, a balanced or unbalanced source?
Balanced sources will have an XLR connector typically whereas unbalanced
sources typically use an RCA phono jack.
2).What type of camcorder are you using? It is normally safe to assume a
consumer camera has -10dBV input but I would prefer to know for sure since
some require a different signal level,
3). Although this is a somewhat minor detail, some camcorders provide DC
power through their MIC-IN jack to support electret or other microphones
requiring a pre-amp / power. I normally would add a little blocking
capacitor in the pad to keep this DC from showing up back at the other end
of the cable at the LineOut device's output stage. If the LineOut device
uses an output transformer, for example, or does not provide a buffered
output, this DV voltage can add an offset/bias which you want to prevent.
Let me know and I will calculate the resistances and give you a design.
Smarty
"Richard Crowley" <richard.7.crowley@intel.com> wrote in message
news:di69dd$ftn$1@news01.intel.com...
| Quote: | "Rick Merrill" wrote ...
Andy & Kim wrote:
Thanks for the advise guy's. Smarty could you give me some values of the
resistors I would need for a T-pad attenuator, just as a guide.
I second the request!
http://www.uneeda-audio.com/pads/
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Smarty
Guest
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| Posted:
Fri Oct 07, 2005 11:51 pm Post subject:
Re: Line into mic input |
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I went to Google to find the design equations for the two resistor values
used in a standard audio T-pad for different attenuation and found, almost
immediately, a really simple to follow "do it yourself" guide at:
http://www.uneeda-audio.com/pads/
which has a nice table at the bottom showing the resistances for an
unbalanced T bad, the type I would personally recommend.
Looks like the shunt resistor, R2, in either case he uses is 150 ohms. And
the series resistor is 2200 to 7500 ohms for R1 and R3 depending upon how
much attenuation you need.
The nominal input voltage will be maybe a 300 or 400 millivolts or so
peak-to-peak for a typical LineOut, and the attenuated signal needs to be a
few millivolts up to maybe 8 or 10 nominally The "k" value used in the table
for computing the resistors is between 30 and 100 (30-40 dB attenuation
range).
The resistors are not dissipating any power to speak of, so 1/8 watt or
greater are fine. Getting the right resistance values may require buying
precision 1% resistors although 150, 2200 and 6800 ohm resistors are
standard 5% parts.
Smarty
"Smarty" <nobody@nobody.com> wrote in message
news:b4KdnRVlopazJNveRVn-jg@adelphia.com...
| Quote: | Glad to assist. I need to know 3 things before designing an attenuator
pad.
1). Where is the Line Output coming from, a balanced or unbalanced source?
Balanced sources will have an XLR connector typically whereas unbalanced
sources typically use an RCA phono jack.
2).What type of camcorder are you using? It is normally safe to assume a
consumer camera has -10dBV input but I would prefer to know for sure since
some require a different signal level,
3). Although this is a somewhat minor detail, some camcorders provide DC
power through their MIC-IN jack to support electret or other microphones
requiring a pre-amp / power. I normally would add a little blocking
capacitor in the pad to keep this DC from showing up back at the other end
of the cable at the LineOut device's output stage. If the LineOut device
uses an output transformer, for example, or does not provide a buffered
output, this DV voltage can add an offset/bias which you want to prevent.
Let me know and I will calculate the resistances and give you a design.
Smarty
"Richard Crowley" <richard.7.crowley@intel.com> wrote in message
news:di69dd$ftn$1@news01.intel.com...
"Rick Merrill" wrote ...
Andy & Kim wrote:
Thanks for the advise guy's. Smarty could you give me some values of
the resistors I would need for a T-pad attenuator, just as a guide.
I second the request!
http://www.uneeda-audio.com/pads/
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