embedding messages (ID numbers) in audio

On Wed, 17 Dec 2008 08:02:03 -0600, Frnak McKenney
<frnak@far.from.the.madding.crowd.com> wrote:


>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.

> ...

>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".

   The way I count, that's two bits (average, with the name number of
1's and 0's) per 640mS, or about 3 bits per second (or is there just
one burst per second? That's only 1 bps), not 30 bits per second.

   Another thing, I wouldn't use 100 Hz (not sure if you were
suggesting actually using that frequency in this app), it's well below
the de facto "standard" 300 to 3,000 Hz voice band, and with all the
filtering used, 100 Hz is likely to be well below the noise.

   Or is this application going to read directly from the A/D the
phone's microphone is connected to? I can still imagine both circuitry
(the capacitor coupling of the mic rolling off below 300 Hz) and
software (the cell phone 'conveniently' filters the mic signal to 300
- 3,000 Hz)
	
>
>
>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

On Wed, 17 Dec 2008 07:04:24 -0800 (PST), dbell <bellda2005@cox.net> wrote:
> On Dec 17, 9:02 am, Frnak McKenney
><fr...@far.from.the.madding.crowd.com> wrote:
>> On Tue, 16 Dec 2008 11:23:58 -0800 (PST), Natalie <natlinn...@gmail.com> wrote:
>> > On Dec 16, 6:09 am, Frnak McKenney
>> ><fr...@far.from.the.madding.crowd.com> wrote:
>> >> Hi, Natalie. Sounds like an interesting problem. <grin!>
>>
>> >> On Mon, 15 Dec 2008 15:25:20 -0800 (PST), Natalie <natlinn...@gmail.com> wrote:
>> >> > Hi everyone,
>> >> > I want to embed ID numbers in audio so that I can recover them on a
>> >> > separate device.
--big snip--
>> > ...  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,

If you're referring to a possible compression algorighm within the 
cellphone network, I don't see it applying to the OP's situation.

As I understand it, the (sound+ID) signal will issue from ElCheapo 
speakers, and will be picked up by the microphone of a nearby
cellphone. The ID part of the signal will then be extracted
"through the magic of DSP!" by the cellphone's microprocessor.

As to what happens then, I forgot to ask.  Text apears on the
cellphone LCD display?  A text message containing the ID code and
the current location/cell tower link gets sent somewhere?


Frank
--
    Statistics are no substitute for judgment.  -- Henry Clay
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)