'morse code' picked up by the speakers

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'morse code' picked up by the speakers

jonetsu@teksavvy.com
Recently the speakers (Yamaha HS5) are 'picking up' 'morse code' (for
lack of better description).  I don't think this goes into any
recording (haven't checked yet).  So, erratically, maybe a few times
per hour, the speakers will put out a short 'morse code' type of beeps,
whether there is music playing or not.  It could be at total idling
time.  They never did that before.

My question is, what is the source of these short beeps ?  Even if they
are not recorded they can be disturbing when improvising or in a quiet
piece.

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Re: 'morse code' picked up by the speakers

Joe Hartley
On Sat, 10 Jun 2017 18:11:48 -0400
jonetsu <[hidden email]> wrote:

> My question is, what is the source of these short beeps ?  Even if they
> are not recorded they can be disturbing when improvising or in a quiet
> piece.

Sounds like interference from your mobile phone.  I can often tell when
I have a text message coming in before the phone notifies me if my phone's
close enough to the speakers.

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Re: 'morse code' picked up by the speakers

Chris Caudle
In reply to this post by jonetsu@teksavvy.com
On Sat, June 10, 2017 5:11 pm, jonetsu wrote:
> Recently the speakers (Yamaha HS5) are 'picking up' 'morse code'

Sounds like typical interference from a GSM phone.  Usually moving the
phone half a meter away should be enough to reduce the interference.

> I don't think this goes into any recording (haven't checked yet).

Probably not assuming you are hearing the interference from the powered
monitors, and not from a mixer, synthesizer, etc. that might be in the
recording chain.

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Re: 'morse code' picked up by the speakers

jonetsu@teksavvy.com
In reply to this post by Joe Hartley
On Sat, 10 Jun 2017 18:25:56 -0400
Joe Hartley <[hidden email]> wrote:

> On Sat, 10 Jun 2017 18:11:48 -0400
> jonetsu <[hidden email]> wrote:
>
> > My question is, what is the source of these short beeps ?  Even if
> > they are not recorded they can be disturbing when improvising or in
> > a quiet piece.
 
> Sounds like interference from your mobile phone.  I can often tell
> when I have a text message coming in before the phone notifies me if
> my phone's close enough to the speakers.

Yes, that's the case.  Just to add to this a tiny bit, cell phone
waves are way up there in the frequencies, so that cannot make such a
low pulsating interference. Not sure, but it seems that the cell phone
waves are modulated in the (very) low frequency range and that
modulation is what's picked up by the (magnet of the) speakers. That
modulation creates another frequency.
 



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Re: 'morse code' picked up by the speakers

Chris Caudle
On Tue, June 13, 2017 12:04 pm, jonetsu wrote:
> Yes, that's the case.  Just to add to this a tiny bit, cell phone
> waves are way up there in the frequencies, so that cannot make such a
> low pulsating interference. Not sure, but it seems that the cell phone
> waves are modulated in the (very) low frequency range

Yes, correct.  GSM is especially bad in that regard, there is a time
period when the signal must either be modulated very heavily, or is going
between on and off or almost off.  Quite annoying, but has the good
property that interference is usually very noticeable, less problem of
wondering if there is or is not a problem.

> modulation is what's picked up by the (magnet of the) speakers.

Unlikely to be the magnet.  The speaker model you mentioned previously is
an active speaker, with an amplifier built in.  The first stage of the
amplifier is likely sensitive to interference.  The junction of a
transistor is the same semiconductor structure as a diode, which can be
used to demodulate AM radio. In essence the amplifier built in to the
speakers was designed without proper protection against radio frequency
interference.

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Chris Caudle


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Re: 'morse code' picked up by the speakers

Jacob-10
In reply to this post by jonetsu@teksavvy.com
Hi,

On 06/13/2017 07:04 PM, jonetsu wrote:
>
> Yes, that's the case.  Just to add to this a tiny bit, cell phone
> waves are way up there in the frequencies, so that cannot make such a
> low pulsating interference. Not sure, but it seems that the cell phone
> waves are modulated in the (very) low frequency range and that
> modulation is what's picked up by the (magnet of the) speakers. That
> modulation creates another frequency.

I'll explain some related GSM basics below, but keep in mind that this
is a quite simplified description.

GSM RF transmission is basically done in bursts with a length of ~ 0.5
ms each. These are organised in frames of 8 timeslots. If the phone
needs to send data (either audio, data, acknowledgements, control
messages), it requests a channel from the network which allocates an
uplink timeslot for the phone. Since each burst may only carry a few
bits (normal burst: 114 data bits brutto minus forward error
correction), you'll need some of them which gives you a sequence of
bursts at a rate of ~ 250Hz (-> audio base frequency). Initially, when
the phone tries to set up a connection it sends a sequence of so-called
RACH bursts on different timeslots with a higher RF power level
(involving some allocation randomness to have a chance to get a free
slot even if another phone tries to do it at the same time). So it
sounds differently at the start of the connection. The transmission
power of your phone can be reduced by the base station later on, so
there can be an audible power reduction step depending on the distance
to the base station. Things get more complicated with GRPS/EDGE (which
can also be used for SMS transmission) because the slot allocation for
packet data can be more dynamic.

If you combine this with a non-linear receiver you just get AM
demodulation of the burst sequence sent by your phone giving you exactly
this kind of sounds.

Jacob
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