Re: embedding messages (ID numbers) in audio

On Dec 17, 9:02 am, Frnak McKenney
<fr...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Tue, 16 Dec 2008 11:23:58 -0800 (PST), Natalie <natlinn...@xxxxxxxxx> wrote:
On Dec 16, 6:09 am, Frnak McKenney
<fr...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi, Natalie. Sounds like an interesting problem. <grin!>

On Mon, 15 Dec 2008 15:25:20 -0800 (PST), Natalie <natlinn...@xxxxxxxxx> wrote:
Hi everyone,
I want to embed ID numbers in audio so that I can recover them on a
separate device.  Some of my constraints:
-The audio will be transmitted from a standard TV/DVD set-up (so DVD
encoding, TV speakers).
-The audio will be received and processed on a cell phone (so cell
phone microphone, processing capabilities (but can be a high-end cell
phone))
-There will be significant background noise picked up by the
microphone

Just to clarify: in your application,

  - The original_sound+ID signal will issue from the speakers of an
    arbitrary consumer-level "off-the-rack" TV set, stereo, or
    similar device, although it might be part of a cable TV channel
    airing, radio broadcast, or a CD or DVD.

  - It will propagate through normal atmosphere for distances of
    (say) 1-20 meters, and is subject to surrounding noise sources
    such as conversations from nearby cubicles, A/C, Muzak&friends,
    toilets flushing in the next room, and so forth.  <grin!>

  - It will be heard by anyone in the surrounding area.

  - It will be picked up by a cellphone (again, an arbitrary
    consumer telephone).

One question:  will the ID be processed by a cellphone app, and,
say, display a message on the cellphone screen?

Or will the cellphone be used as a dial-in microphone, that is, will
it send the audio signal to some fixed remote site where your
application will process it?

-The ID numbers will occur about every 30 seconds, and each needs to
be about 10-12 bits of data.
-It would be vastly preferable if the encoding didn't alter the
original audio track significantly; that is, if people listening to
the audio couldn't really tell that there was data embedded in the
audio

For example, if you were designing a system that would (say) allow
an advertising agency representative to walk into a TV store with a
cellphone and find out which of their ads were showing at the
moment.  Mixing in (say) high-volume DTMF (touch-tone) digits every
30 seconds would accomplish your _ID_ purpose, but it might be
considered somewhat...  distracting.  <grin!>

I've looked at the literature on audio watermarking, but this seems to
differ from what I want to do in a couple of significant ways:
-I'm not worried about a malicious attacker, so detection and spoofing
aren't concerns
-I'm broadcasting over a very noisy channel

I'd appreciate any info that people could point me toward -
applications, literature, websites, whatever.

I don't know if it will work over a cellphone link, and the data
rate may not meet your specifications, but the NIST WWV time
broadcasts contain digital data mixed in with audio by using a 100Hz
subcarrier.  You can obtain a description of the format used from
NIST Special Publication 250-67 "NIST Time and Frequency Radio
Stations" by searching for "250-67" at:

   National Institute of Standards and Technology
   http://www.nist.gov/

Whatever method you finally choose, given the possible variations in
ambient noise I think you ought to assume that the delived signal
would be extremely error-prone (in multiple ways), and
intermittently delivered (cell signal loss, PA loudspeaker, etc.)
and plan accordingly.

--snip--

Ah!  So sorry not to be completely clear.  You were correct on all
your clarifying points.

S'OK. It's difficult to absorb many details in one pass. For
example, it wasn't until this re-(re-*)reading of your original post
that I finally read the phrase "about 10-12 bits of data" correctly:
I had been reading it as "bytes. <grin!>

Which means that the NIST WWVx encoding of one pulse per second
would give you 30 bits/second, enough for some redundancy/error
correction.  You will also need some sort of "preamble" or distinct
synchronization pattern so the software dan tell when the ID
bitstream begins.

...  As to your question:  I'd like to do the
processing _on_ the cellphone.

Ah.  That's good:  you don't need to worry about any mashing of the
sound signal within the cellphone network.

How do you figure? Are you counting on compression algorithms to
reliably reproduce what you cannot hear above the regular audio?

Dirk


But it could make the software development and distribution a bit
trickier if your application needs to be able to executed on
AnyOldCellphone(tm), including the SuperSecret Model X With
"Revolutionary DSP-Based Investment Analysis", which will be
announced next Friday.  ("But wait!  There's more!  ...  <grin!>)

...  Thanks for the pointers, I'm reading
through the docs.  This isn't my specialty, so it's kinda slow
going.  :)

If it helps, the WWV stuff is encoded as narrow (170ms=0) and wide
(470ms=1) bursts of 100Hz tone.  From your point of view, I think,
what's important is "my software can tell the difference between a
1, a 0, and nothing" and "most people don't notice it".

Frank McKenney
--
   Physics is mathematical not because we know so much about the
   physical world, but because we know so little; it is only its
   mathematical properties that we can discover.
                             -- Bertrand Russell
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)- Hide quoted text -

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