Ultrasonic communication with consumer devices

Hi all,

lately, there are more and more news about communication,
using ultrasonic sound data transmission, between consumer
devices, like smartphones.

Here some links:

https://www.newscientist.com/article/2110762-your-homes-online-gadgets-could-be-hacked-by-ultrasound/
http://arstechnica.com/tech-policy/2015/11/beware-of-ads-that-use-inaudible-sound-to-link-your-phone-tv-tablet-and-pc/

I was wondering, is it really technically possible to use
devices, which are designed to generate and pick up sound
at barely 20Hz-20KHz range, to work above 20KHz.

I mean, assuming the microphone is sampled at 44.1KHz, there
is not too much margin to pick up something above 20KHz,
considering the analogue anti aliasing filter performances too.
Same story for the loudspeakers.

Am I missing something?
Is it really technically possible to pick up and generate
ultrasound signals with a consumer smartphone?
Or PC, for what that matter...

Thanks,

bye,

-- 

piergiorgio

On Friday, November 11, 2016 at 5:28:18 PM UTC-5, Piergiorgio Sartor wrote:
> Hi all,
> 
> lately, there are more and more news about communication,
> using ultrasonic sound data transmission, between consumer
> devices, like smartphones.
> 
> Here some links:
> 
> https://www.newscientist.com/article/2110762-your-homes-online-gadgets-could-be-hacked-by-ultrasound/
> http://arstechnica.com/tech-policy/2015/11/beware-of-ads-that-use-inaudible-sound-to-link-your-phone-tv-tablet-and-pc/
> 
> I was wondering, is it really technically possible to use
> devices, which are designed to generate and pick up sound
> at barely 20Hz-20KHz range, to work above 20KHz.
> 
> I mean, assuming the microphone is sampled at 44.1KHz, there
> is not too much margin to pick up something above 20KHz,
> considering the analogue anti aliasing filter performances too.
> Same story for the loudspeakers.
> 
> Am I missing something?
> Is it really technically possible to pick up and generate
> ultrasound signals with a consumer smartphone?
> Or PC, for what that matter...
> 
> Thanks,
> 
> bye,
> 
> -- 
> 
> piergiorgio

Whether it's technically possible is certainly true, because there are already real devices using this. Google's Chromecast, and there's also a Chrome extension (Google Tone) by Google that shares links with ultrasonic sounds. My office had a lot of fun with it when it was first released, so it definitely works.

I just did some tests with a spectral analyzer app and my LG G3 and got great results. I placed the phone on the other side of a (small) room from a Macbook and used Reaper's 'Sine Sweep Generator' tool with the sampling rate set to 48khz. There was a TV in the same room playing something on Netflix to give some background noise.

http://i.imgur.com/VhFmq4c.png
http://i.imgur.com/SAHaqE9.png

The first screenshot is a 10-second sweep up to 22050 hz, the second are two sweeps up to 44100 hz. The signal above 15k is surprisingly clear for two devices that have no real need to output/record those frequencies.

Lastly, here's a screenshot of the spectrum generated by the "Google Tone" extension. I used it three times with a pause in between each. It makes some 'computery' tones around 1k to show that it's working, but you can clearly see that the real data is transmitted in a range roughly from 18k-20k.

http://i.imgur.com/AtiwNS7.png

If anyone else knows more about this, I'm also very interested in hearing more.

Cheers,
Neil

Piergiorgio Sartor  

>lately, there are more and more news about communication,
>using ultrasonic sound data transmission, between consumer
>devices, like smartphones.

>Here some links:
>
>https://www.newscientist.com/article/2110762-your-homes-online-gadgets-could-be-hacked-by-ultrasound/
>http://arstechnica.com/tech-policy/2015/11/beware-of-ads-that-use-inaudible-sound-to-link-your-phone-tv-tablet-and-pc/

>I was wondering, is it really technically possible to use
>devices, which are designed to generate and pick up sound
>at barely 20Hz-20KHz range, to work above 20KHz.

Yes. 

>I mean, assuming the microphone is sampled at 44.1KHz

It isn't.

>Same story for the loudspeakers.

The speakers have less ultrasonic response then the microphones.

>Is it really technically possible to pick up and generate
>ultrasound signals with a consumer smartphone?

Yes. 

Note, most devices are leaking a sound signal at around 30 KHz
(the sleep clock).

Steve

Thanks both for the answers.

On 2016-11-12 01:04, Steve Pope wrote:
[..]
>> I mean, assuming the microphone is sampled at 44.1KHz
> 
> It isn't.

Why it isn't? And how is it?

>> Same story for the loudspeakers.
> 
> The speakers have less ultrasonic response then the microphones.

Meaning that a device can pick, but it cannot
generate, right?
Then, how does the communications happen?

>> Is it really technically possible to pick up and generate
>> ultrasound signals with a consumer smartphone?
> 
> Yes. 
> 
> Note, most devices are leaking a sound signal at around 30 KHz
> (the sleep clock).

Well, one more reason *not* to have mikes capable
of ultrasound pick up.

I'm a bit puzzled.
While the mikes clearly are more sensible, the
loudspeakers are usually not.
At least, this is what I understood from your
explanation.

But, apart from the experimental evidence, why
such mikes are built in consumer devices which,
in principle, are intended for voice (I know,
maybe someone will record more than voice, but
still...)?

bye,

-- 

piergiorgio

Piergiorgio Sartor  

>On 2016-11-12 01:04, Steve Pope wrote:

>> The speakers have less ultrasonic response then the microphones.

>Meaning that a device can pick, but it cannot
>generate, right?
>Then, how does the communications happen?

I said "less", I did not say "none".

>But, apart from the experimental evidence, why
>such mikes are built in consumer devices which,
>in principle, are intended for voice (I know,
>maybe someone will record more than voice, but
>still...)?

I think it's mostly that these transducers are very small --
in the case of the microphones, extremely tiny -- and small
transducers tend to have better high frequency response.
They may not be spec'ed to work at ultrasonic but it turns
out they do.

(Or it may be, there are enough ultrasonic applications that
they have now spec'ed this in.)

Steve

On 2016-11-12 17:05, Steve Pope wrote:
> Piergiorgio Sartor  
> 
>> On 2016-11-12 01:04, Steve Pope wrote:
> 
>>> The speakers have less ultrasonic response then the microphones.
> 
>> Meaning that a device can pick, but it cannot
>> generate, right?
>> Then, how does the communications happen?
> 
> I said "less", I did not say "none".

Well, this is the question.
In my experience, which might be old, the crappy
loudspeakers barely can reproduce above 15KHz, the
good ones.

Furthermore, the sampling rate could easily be
32KHz, maybe 44.1KHz. 48KHz? Really? Even if
this is used, how about the low-pass filter?
Would this allow more than 20KHz?

[...]
> I think it's mostly that these transducers are very small --
> in the case of the microphones, extremely tiny -- and small
> transducers tend to have better high frequency response.
> They may not be spec'ed to work at ultrasonic but it turns
> out they do.

Yep, but also the ADC has to support it or each
ultrasonic sound will be recorded as alias...
And the analogue part too.

> (Or it may be, there are enough ultrasonic applications that
> they have now spec'ed this in.)

Uhm, that would be interesting, really...

bye,

-- 

piergiorgio

On Friday, November 11, 2016 at 5:28:18 PM UTC-5, Piergiorgio Sartor wrote:
> Hi all,
> 
> lately, there are more and more news about communication,
> using ultrasonic sound data transmission, between consumer
> devices, like smartphones.
> 
> Here some links:
> 
> https://www.newscientist.com/article/2110762-your-homes-online-gadgets-could-be-hacked-by-ultrasound/
> http://arstechnica.com/tech-policy/2015/11/beware-of-ads-that-use-inaudible-sound-to-link-your-phone-tv-tablet-and-pc/
> 
> I was wondering, is it really technically possible to use
> devices, which are designed to generate and pick up sound
> at barely 20Hz-20KHz range, to work above 20KHz.
> 
> I mean, assuming the microphone is sampled at 44.1KHz, there
> is not too much margin to pick up something above 20KHz,
> considering the analogue anti aliasing filter performances too.
> Same story for the loudspeakers.
> 
> Am I missing something?
> Is it really technically possible to pick up and generate
> ultrasound signals with a consumer smartphone?
> Or PC, for what that matter...
> 
> Thanks,
> 
> bye,
> 
> -- 
> 
> piergiorgio

Ultrasound for communication ?

What's wrong with RF, Bluetooth or WiFi for example ?

RF does'n require line of sight visibility and transmission rate is a lot higher

The thing with ultrasound is that unfortunately you can't use Frequency Modulation - there is no practical way to generate a frequency-modulated ultrasonic signals in consumer devices (say around 40KHz which is safe for dogs, cats and other animals)
all piezo transducers sold today are high Q so they all work very close to their resonant frequency - usually 40KHz, or 25 Khz (not good for dogs and cats)
Bats in nature do it somehow, but I am unaware of any cheap ultrasonic transducer capable of outputting ultrasonic waves of changing frequencies

Which limits you to AM modulation only - in practice just on-off switching 

On the other hand, microphones pick up ultrasound very well, even the cheap electret capsules (well into 40-60 KHz range), you just need some analog filters with preamp and a proper ADC (at least 96Ks/s)

Still it's hard to justify utility of this for communication at practical frequency ranges (25 Khz and higher)

On 11/12/2016 11:19 AM, Piergiorgio Sartor wrote:
> On 2016-11-12 17:05, Steve Pope wrote:
>> Piergiorgio Sartor
>>
>>> On 2016-11-12 01:04, Steve Pope wrote:
>>
>>>> The speakers have less ultrasonic response then the microphones.
>>
>>> Meaning that a device can pick, but it cannot
>>> generate, right?
>>> Then, how does the communications happen?
>>
>> I said "less", I did not say "none".
>
> Well, this is the question.
> In my experience, which might be old, the crappy
> loudspeakers barely can reproduce above 15KHz, the
> good ones.
>
> Furthermore, the sampling rate could easily be
> 32KHz, maybe 44.1KHz. 48KHz? Really? Even if
> this is used, how about the low-pass filter?
> Would this allow more than 20KHz?

Many of the CODECs used are capable of double rate (96 kHz) or even quad 
rate sampling (192 kHz).  The low pass filter is adjusted accordingly. 
Even so, the filter is also not a brick wall at 20 kHz just as the 
response of the speaker and mic do not drop off abruptly.  The filters 
in such devices is usually tied to the sample rate, often only being 3 
dB down at Fs/2.  (the audio sample rate of a sigma-delta ADC/DAC is 
much higher than the rate of the data words).


>> I think it's mostly that these transducers are very small --
>> in the case of the microphones, extremely tiny -- and small
>> transducers tend to have better high frequency response.
>> They may not be spec'ed to work at ultrasonic but it turns
>> out they do.
>
> Yep, but also the ADC has to support it or each
> ultrasonic sound will be recorded as alias...
> And the analogue part too.

That's not an issue unless there is a steep analog anti-alias filter 
which sigma-delta devices don't need.


>> (Or it may be, there are enough ultrasonic applications that
>> they have now spec'ed this in.)
>
> Uhm, that would be interesting, really...

-- 

Rick C

On Saturday, November 12, 2016 at 12:59:51 PM UTC+13, Neil Goldman wrote:
> On Friday, November 11, 2016 at 5:28:18 PM UTC-5, Piergiorgio Sartor wrote:
> > Hi all,
> > 
> > lately, there are more and more news about communication,
> > using ultrasonic sound data transmission, between consumer
> > devices, like smartphones.
> > 
> > Here some links:
> > 
> > https://www.newscientist.com/article/2110762-your-homes-online-gadgets-could-be-hacked-by-ultrasound/
> > http://arstechnica.com/tech-policy/2015/11/beware-of-ads-that-use-inaudible-sound-to-link-your-phone-tv-tablet-and-pc/
> > 
> > I was wondering, is it really technically possible to use
> > devices, which are designed to generate and pick up sound
> > at barely 20Hz-20KHz range, to work above 20KHz.
> > 
> > I mean, assuming the microphone is sampled at 44.1KHz, there
> > is not too much margin to pick up something above 20KHz,
> > considering the analogue anti aliasing filter performances too.
> > Same story for the loudspeakers.
> > 
> > Am I missing something?
> > Is it really technically possible to pick up and generate
> > ultrasound signals with a consumer smartphone?
> > Or PC, for what that matter...
> > 
> > Thanks,
> > 
> > bye,
> > 
> > -- 
> > 
> > piergiorgio
> 
> Whether it's technically possible is certainly true, because there are already real devices using this. Google's Chromecast, and there's also a Chrome extension (Google Tone) by Google that shares links with ultrasonic sounds. My office had a lot of fun with it when it was first released, so it definitely works.
> 
> I just did some tests with a spectral analyzer app and my LG G3 and got great results. I placed the phone on the other side of a (small) room from a Macbook and used Reaper's 'Sine Sweep Generator' tool with the sampling rate set to 48khz. There was a TV in the same room playing something on Netflix to give some background noise.
> 
> http://i.imgur.com/VhFmq4c.png
> http://i.imgur.com/SAHaqE9.png
> 
> The first screenshot is a 10-second sweep up to 22050 hz, the second are two sweeps up to 44100 hz. The signal above 15k is surprisingly clear for two devices that have no real need to output/record those frequencies.
> 
> Lastly, here's a screenshot of the spectrum generated by the "Google Tone" extension. I used it three times with a pause in between each. It makes some 'computery' tones around 1k to show that it's working, but you can clearly see that the real data is transmitted in a range roughly from 18k-20k.
> 
> http://i.imgur.com/AtiwNS7.png
> 
> If anyone else knows more about this, I'm also very interested in hearing more.
> 
> Cheers,
> Neil

Could you use a Bode plot please, those intensity things mean nothing unless there is statistical varying data of some sort like speech

> Could you use a Bode plot please, those intensity things mean nothing unless there is statistical varying data of some sort like speech

Maybe I'm misunderstanding, but wouldn't that only show frequency response, and not details like if one device could be heard above background noise of other devices? Frequency response on its own doesn't seem that important, as long as it does extend to 20k and there is a good SNR between the high frequency signal and the background.

Wouldn't a show playing on Netflix in the background, or the signal generated by Google Tone be a suitable statistical varying data? And wouldn't a Bode plot be different based on the broadcasting device, the listening device and the room?

(not being sarcastic in case it reads that way, sincerely asking)
Thanks