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DVD player audio distortion

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August 6, 2004 4:22:35 PM

Archived from groups: rec.audio.tech (More info?)

Hi all!

I'm not very knowledgeable about things audio, so I hope that someone
can offer me an opinion. I'm using a Sony 5-disc DVD player
(DVP-NC600) as a CD player, and I've started to notice that on "hot"
(high-level) portions of songs that there can be a distortion-type
sound. I don't know what clipping really sounds like, but the sounds
(often with a louder vocal section in a song) remind me of a singer
singing too loudly into a mic and overloading it. It isn't a problem
on DVDs, and I am wondering if this is a recent problem (components
have been in storage for 3 months).

Anyways: I have been messing around a bit trying to figure out what
the problem is. The problem lessens, but doesn't go away entirely, if
I use the "audio attenuation" feature of the DVD player. I don't like
to use it, because I presume it changes the quality of the sound.

Also, this particular DVD player has two sets of analog audio outputs
(one L/R RCA pair and a second L/R RCA pair). I have one set running
to my amp (NAD C350) and one set running to the TV. If I disconnect
the pair running to the TV and just retain the connection to the amp,
things clear up almost completely. Strangely, the harshness problem
also seems to go away if I listen to the sound from the DVD player
through the TV inputs, out from the TV outputs to the amp (problem is
with direct connection from player to amp).

Question: is this indicative of a problem with the DVD player, or is
this behaviour what one should expect? If so, what's the explanation
behind why this is happening? Is the use of both connections splitting
the available output signal from the DVD player and therefore causing
problems?

Thanks for any insights you all might have!
Anonymous
August 7, 2004 12:25:46 AM

Archived from groups: rec.audio.tech (More info?)

In article <1a4a0d12.0408061122.6c087aad@posting.google.com>,
tk <thekenward@yahoo.com> wrote:

>Also, this particular DVD player has two sets of analog audio outputs
>(one L/R RCA pair and a second L/R RCA pair). I have one set running
>to my amp (NAD C350) and one set running to the TV. If I disconnect
>the pair running to the TV and just retain the connection to the amp,
>things clear up almost completely. Strangely, the harshness problem
>also seems to go away if I listen to the sound from the DVD player
>through the TV inputs, out from the TV outputs to the amp (problem is
>with direct connection from player to amp).
>
>Question: is this indicative of a problem with the DVD player, or is
>this behaviour what one should expect?

This sounds to me as if it's due to a combination of design problems:

[1] The DVD player's audio output is at a relatively high voltage
level, when playing CDs. [This is likely not a design problem,
just a contributor.]

[2] The TV set's audio inputs are placing some sort of unusual
electrical load on the circut, under some circumstances. It's not
unusual for a component's audio inputs to behave something like a
short circuit, or like a set of back-to-back diodes, if the
component is powered off.

[3] The DVD player's outputs have a relatively high output impedance,
or low current-drive capability.

So, if you're got the DVD player connected to both the amp and the TV,
and the TV is turned off, and you play a CD at full volume, the
following might happen:

- On peaks, the DVD player's output voltage is relatively high (2
volts peak-to-peak is standard for CD player outputs).

- The output voltage is high enough to force the input circuitry in
the TV set's audio input to start presenting an unusual load...
e.g. it exceeds .7 volts from ground, and a protective diode starts
conducting.

- The DVD player can't "push" enough current into the signal to
overcome the conduction in the TV set input, and thus cannot
raise the signal voltage above the limit set by the TV set. This
"clips" off the top of each cycle of the audio waveform, causing
severe distortion.

- The amp sees the clipped waveform rather the original signal, and
amplifies the distortion.

The problem would go away if you disconnect the TV set (removes the
unusual clip-inducing load from the line), or reduce the volume level
(keeps the DVD player's output voltage below the point at which the TV
set's circuitry starts clipping it), or play a DVD (lower audio
level?). Might also go away if you turn on the TV set, if the TV
set's protective circuit is clamping to signal to "DC voltage supply
+/- .7 volts" rather than to "ground +/- .7 volts"

One possible workaround would be to build yourself a resistive
isolator at the TV set input. Just install a 1k or 4k resistor in
series with each of the two channels' audio signals, just before the
signal enters the TV set jack. This will limit the current flow into
the TV set's circuitry, greatly reducing the degree to which the
protective circuitry's unusual load is "seen" by the DVD player, and
should eliminate the clipping.

Similar problems have existed for years. For example, some
better-quality audio preamps have separate buffer circuits to drive
their "to tape recorder" outputs, so that a tape recorder wouldn't
load down and distort the primary audio signal if it were powered off.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
August 11, 2004 4:01:43 PM

Archived from groups: rec.audio.tech (More info?)

Thanks for the reply!

dplatt@radagast.org (Dave Platt) wrote in message news:<10h7qaa4mcvhd69@corp.supernews.com>...

> One possible workaround would be to build yourself a resistive
> isolator at the TV set input. Just install a 1k or 4k resistor in
> series with each of the two channels' audio signals, just before the
> signal enters the TV set jack. This will limit the current flow into
> the TV set's circuitry, greatly reducing the degree to which the
> protective circuitry's unusual load is "seen" by the DVD player, and
> should eliminate the clipping.
>
> Similar problems have existed for years. For example, some
> better-quality audio preamps have separate buffer circuits to drive
> their "to tape recorder" outputs, so that a tape recorder wouldn't
> load down and distort the primary audio signal if it were powered off.

Do you think that adding an audio transformer (like a ground loop
isolator) between the DVD player and the TV would have any beneficial
effect at all?
Related resources
Anonymous
August 12, 2004 1:16:02 PM

Archived from groups: rec.audio.tech (More info?)

thekenward@yahoo.com (tk) wrote in message news:<1a4a0d12.0408111034.19eabfa4@posting.google.com>...
> Thanks for the reply!
>
> dplatt@radagast.org (Dave Platt) wrote in message news:<10h7qaa4mcvhd69@corp.supernews.com>...
>
> > One possible workaround would be to build yourself a resistive
> > isolator at the TV set input. Just install a 1k or 4k resistor in
> > series with each of the two channels' audio signals, just before the
> > signal enters the TV set jack. This will limit the current flow into
> > the TV set's circuitry, greatly reducing the degree to which the
> > protective circuitry's unusual load is "seen" by the DVD player, and
> > should eliminate the clipping.
> >
> > Similar problems have existed for years. For example, some
> > better-quality audio preamps have separate buffer circuits to drive
> > their "to tape recorder" outputs, so that a tape recorder wouldn't
> > load down and distort the primary audio signal if it were powered off.
>
> Do you think that adding an audio transformer (like a ground loop
> isolator) between the DVD player and the TV would have any beneficial
> effect at all?

Why not just run 1 pair of RCA Line outs in series?? One L-R pair goes
from the DVD unit to the amp, then the amp feeds a another L-R pair
from the Tape rec or out jacks on the amp to your TV. It doesn't solve
the problem, but gets around it with a minor re-work of the cabling.

CD
August 13, 2004 3:00:09 AM

Archived from groups: rec.audio.tech (More info?)

Hi!

codifus@optonline.net (Codifus) wrote in message > Why not just run 1 pair of RCA Line outs in series?? One L-R pair goes
> from the DVD unit to the amp, then the amp feeds a another L-R pair
> from the Tape rec or out jacks on the amp to your TV. It doesn't solve
> the problem, but gets around it with a minor re-work of the cabling.

Brilliant idea! Tried it! Didn't work! :o (

Did some cable rerouting to experiment, though. With both the DVD
player's L/R outs connected to two different source inputs on the amp,
no distortion was heard with either source selected at the amp.

If the only analog audio connection is from DVD player to amp, no
distortion results. If just one more analog audio connection is made,
from DVD player to TV analog audio inputs (tried two different input
sets as well), there is distortion. I suspect Dave was right --
something is going on at the TV end. I sent the TV in for a check
under warranty -- no faults were found in the electronics, so there
must be some design characteristics that cause the problem.

I will try an audio isolator -- maybe that will work?
Anonymous
August 14, 2004 2:13:34 AM

Archived from groups: rec.audio.tech (More info?)

tk wrote:
> Hi!
>
> codifus@optonline.net (Codifus) wrote in message > Why not just run 1 pair of RCA Line outs in series?? One L-R pair goes
>
>>from the DVD unit to the amp, then the amp feeds a another L-R pair
>>from the Tape rec or out jacks on the amp to your TV. It doesn't solve
>>the problem, but gets around it with a minor re-work of the cabling.
>
>
> Brilliant idea! Tried it! Didn't work! :o (
>
> Did some cable rerouting to experiment, though. With both the DVD
> player's L/R outs connected to two different source inputs on the amp,
> no distortion was heard with either source selected at the amp.
>
> If the only analog audio connection is from DVD player to amp, no
> distortion results. If just one more analog audio connection is made,
> from DVD player to TV analog audio inputs (tried two different input
> sets as well), there is distortion. I suspect Dave was right --
> something is going on at the TV end. I sent the TV in for a check
> under warranty -- no faults were found in the electronics, so there
> must be some design characteristics that cause the problem.
>
> I will try an audio isolator -- maybe that will work?
Hmmm, this is a bit of a stretch to suggest, but perhaps a ground loop
problem is a catalyst to this audio distortion that you're experiencing?
Is your TV connected to cable TV? Try dis-connecting all cable TV
connections and see how the stereo sounds with all the RCAs hooked up.

CD
August 14, 2004 4:04:24 AM

Archived from groups: rec.audio.tech (More info?)

Hey, thanks for your interest in the problem!

Codifus <codifus@optonline.net> wrote in message news:<cfjsfu$1cmt$1@news.interpublic.com>...
> Hmmm, this is a bit of a stretch to suggest, but perhaps a ground loop
> problem is a catalyst to this audio distortion that you're experiencing?
> Is your TV connected to cable TV? Try dis-connecting all cable TV
> connections and see how the stereo sounds with all the RCAs hooked up.

Like I said, the problem occurs with the only connections in the
system being from DVD player to amp and from DVD player to TV. It
doesn't matter if the TV is plugged in to AC power or not.

I have a kludgey fix right now -- using an inexpensive Radio Shack AV
switcher. Normally it's used to take two sets of Video/R/L inputs and
allow you to select either set for output. I'm connecting the "outs"
of the unit to one set of the DVD player's outputs, and using the
"inputs" of the unit as outputs to the amp and TV. I figure it's like
having a Y-splitter where I can choose which branch of the Y to use by
selecting a switch position. I don't know if it's a very clean
solution, but it has improved things for now.
Anonymous
August 16, 2004 1:31:53 AM

Archived from groups: rec.audio.tech (More info?)

tk wrote:

> Hey, thanks for your interest in the problem!
>
> Codifus <codifus@optonline.net> wrote in message news:<cfjsfu$1cmt$1@news.interpublic.com>...
>
>>Hmmm, this is a bit of a stretch to suggest, but perhaps a ground loop
>>problem is a catalyst to this audio distortion that you're experiencing?
>>Is your TV connected to cable TV? Try dis-connecting all cable TV
>>connections and see how the stereo sounds with all the RCAs hooked up.
>
>
> Like I said, the problem occurs with the only connections in the
> system being from DVD player to amp and from DVD player to TV. It
> doesn't matter if the TV is plugged in to AC power or not.
>
> I have a kludgey fix right now -- using an inexpensive Radio Shack AV
> switcher. Normally it's used to take two sets of Video/R/L inputs and
> allow you to select either set for output. I'm connecting the "outs"
> of the unit to one set of the DVD player's outputs, and using the
> "inputs" of the unit as outputs to the amp and TV. I figure it's like
> having a Y-splitter where I can choose which branch of the Y to use by
> selecting a switch position. I don't know if it's a very clean
> solution, but it has improved things for now.
I wasn't talking about AC power;) Dis-connect the cable from the TV and
see what happens . . . the cable that feeds in the channels that you watch.

CD
August 17, 2004 4:40:52 AM

Archived from groups: rec.audio.tech (More info?)

Codifus <codifus@optonline.net> wrote in message news:<cfp2pn$300a$3@news.interpublic.com>...
> I wasn't talking about AC power;) Dis-connect the cable from the TV and
> see what happens . . . the cable that feeds in the channels that you watch.

I should have been more clear; I have tried it with and without the
cable connected to the coax input on the set, and there is no
difference. A friend who is an electronics tech thinks Dave Platt
(above) may indeed have hit on the right idea; of course it's hard to
say without having a look at the TV's innards, and I'm not sure either
my friend or I are that ambitious!
August 17, 2004 5:18:18 AM

Archived from groups: rec.audio.tech (More info?)

Codifus <codifus@optonline.net> wrote in message news:<cfp2pn$300a$3@news.interpublic.com>...
> I wasn't talking about AC power;) Dis-connect the cable from the TV and
> see what happens . . . the cable that feeds in the channels that you watch.

I should have been more clear; I have tried it with and without the
cable connected to the coax input on the set, and there is no
difference. A friend who is an electronics tech thinks Dave Platt
(above) may indeed have hit on the right idea; of course it's hard to
say without having a look at the TV's innards, and I'm not sure either
my friend or I are that ambitious!
!