Neutralizing the iOS camera click sound through active sound cancellation | Hacker News Reader

Neutralizing the iOS camera click sound through active sound cancellation

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334 pointsdmd105 comments

I wonder if Apple is intentionally forcing the shutter sound, to prevent secret upskirt shots. I know several phones have had shutter sounds that cannot be disabled, and some countries have required it. In that case Apple might reject apps that use this trick.

End user can use the mute switch to turn off the sound. This question is about doing it programmatically.

In Japan, the iPhone will always have the shutter sound even with mute on. You can't disable it or mute it. Even if you didn't buy the phone in Japan, the iPhone will do that in Japan.

I've been to Japan, and my iPhone didn't make any shutter sounds while I was there.

Now the question is - how would the iPhone even know that's in Japan? :) GPS? I think OS X uses the time zone for these things, e.g. to block certain WiFi channels due to legal requirements.

Well, it is a phone... It's going to have access to geo data from the local cell phone towers, no timezone hacks necessary. In fact I believe the iPhone adjusts your active timezone automatically according to the geo data collected from the local cell tower, hence why your phone time changes when you touch down after a long flight.

Actually the time update is not based on inference from location data, but rather it is actively transmitted by the cell network as part of the GSM standard.

http://en.wikipedia.org/wiki/NITZ

Though it's possibly worth pointing out that time/date is not a _requirement_ to the standard and not all networks implement it. It's possibly also worth pointing out that most recent Android devices seem to use NTP at the OS level rather than relying on GSM broadcast info.

As the other poster said, time has it's own standard. In terms of your reply to OP, it's even simpler. The network identifier for an operator broadcast by the cell tower consists of a network code and a country code :)

Actually blocking WiFi channels is done through the 802.11d information element in WiFi beacons which specify what the country the access point is in.

Maybe it is also transmitted that way, but changing the time zone from Australia from New Guinea has repeatedly fixed my OS X WiFi issues when a Chinese roommate used an illegal channel (in Australia).

It will be connected to a telco network, right? That's how it knows in what country it is. In Europe it is quite common to cross countries borders and as soon as you get connected to your neighbours telco you get a text welcoming you to the country.

But then they'd have to come up with a different solution for the iPod touch :)

Are you sure? I thought regulation-specific stuff like this was baked into the firmware via flags that checked the hardware model number.

For example: my iPhone 5, which I bought in China, cannot make or receive voice-only FaceTime calls. Even if I am in the US, using a US SIM, this is the case. It's not related to the GPS or cell tower location, or to the time zone.

Um, no. I just found out about the issue as I bought a Japanese iPhone5S in January and promptly returned it the next day because I couldn't turn off the camera sound. I picked up a USA iPhone5S in Hawaii in February. Have been back in Japan for 2 months now. No sounds coming out of my camera on my USA iPhone5S.

The thing that makes this most ridiculous is (a) they don't have the same requirement of digital cameras in Japan and (b) 3rd party camera apps you download for phones are not required to make a sound. Pretty much every Japanese person downloads another camera app for exactly that reason.

Me personally, I just don't want the sound. Sitting in a quiet restaurant taking stupid pictures of my food with my phone is already embarrassing enough without calling myself out with my phone making noise. Hence getting the USA model. Sure I could have used separate camera software but I wanted to be able to use the camera app that doesn't require me to unlock the phone without sound.

Film cameras: SLRs are big and obvious, Leicas not so much but still fairly obvious. The Rolleiflex medium format dual lens reflex camera has a leaf shutter and is very quiet at the time of exposure and is held at waist height. Popular with portrait photographers. However a Rollei is not easily concealed. Taking any of these cameras out is a serious undertaking. Bag, film, camera, various extras. Not casual.

I suppose the advent of high quality cameras that are always carried as part of a phone coupled with the very small size of the phone has lead some countries to evolve these regulations.

Perhaps an actual digital camera is felt to fall in the 'not casual' category, so not covered by the regulation?

I'm not sure what casual has to do with it. People that want to take up skirt shots aren't casual and they can buy keychain video cameras for $4 a piece on eBay and stick them in their shoes

The laws in Japan that require sounds for the phone are as stupid as punishing legit software purchasers with anti-copying measures. They only hurt the legit people and don't at all hinder the undesirable behavior

Leica has digital cameras these days, you know :)

I know. But not as weighty as my old M4.

So now i want to take snaps of my meals with a medium format camera.

> The thing that makes this most ridiculous is (a) they don't have the same requirement of digital cameras in Japan and (b) 3rd party camera apps you download for phones are not required to make a sound. Pretty much every Japanese person downloads another camera app for exactly that reason.

iPhone's bought in a lot of countries in the Middle East are equally ridiculous as they disable FaceTime (i.e. there is no FaceTime app). Even if you leave the Middle East, e.g. go to the UK and put a UK SIM in, FaceTime is still disabled. Same if you reformat even after doing that, so it's locked at the hardware level. Taking another iPhone to the Middle East works fine (although in most places it still won't actually work as the countries have internet level filtering in place).

The funny thing is you can still download Skype from the App Store and use that without restrictions :)

First I'd heard of this, curious! What's the reasoning behind banning FaceTime?

I'd hazard a guess that it's because Islam technically prohibits images of people's faces?

Middle East countries treat phone and internet as a source of revenue rather than as fundamental business- entrepreneur-enabling infrastructure.

So they're concerned that Facetime, maybe particularly Facetime audio, cannibalizes their mobile network call revenue. Yes, Skype and other alternatives may still be available, but Facetime is integrated into the iOS address book and pressing the "call with facetime" button is just as convenient as dialing a contact's phone number.

I saw this crushingly-self-harmful behavior when I lived in the region and experienced expensive, slow Internet access. They also ban ISPs from buying bandwidth from anyone other than a massively-overpriced state monopoly pipe. If they treated mobile and internet as a key enabling infrastructure instead, the massive expansion in business would result in much higher tax revenue than the hit to the measly communications tolls. But they're either short-termist or have friends who personally profit from the telecom departments.

Plain and simple: State capitalism runs the risk of cronyism, corruption, regulatory capture, etc. Singapore is a good example of state capitalism with relatively low levels of all of these.

I thought was disabled as a compromise because they refused to give those governments the ability to decrypt it. BBM had similar issues.

http://appadvice.com/appnn/2010/09/unconfirmed-saudi-arabia-...

It's still kind of a joke, since you can mute an iPhone very effectively by covering up the speaker holes.

Like most things it is a good enough solution, not a perfect solution.

Isn't the shutter sound, even where required by law, kind of pointless because unsavory users could just take a video instead of taking a picture? That's probably what perverts prefer anyway.

A true pervert ostensibly might appreciate the additional megapixels offered by a still image over under-sampled auto-compressed video.

A quality-minded pervert would probably just buy a $150 digital point-n-shoot. Just as many megapixels, no shutter sound, and much better optical components.

A technical pervert would take a HD video with their phone and then use multiple frames to mathematically extract even higher-resolution stills from it:

http://www.eecs.harvard.edu/~kalyans/research/snapshots/supp...

Let's hope to God people on Hacker News don't start taking upskirt shots.

They would get in arguments about the latest up-sampling frameworks and never ship anything.

"I'm not a pervert! I'm testing my app which has a target market of perverts!"

and people in the train will see you with a digital camera instead of a multi-use device like a phone.

Yes, I believe Apple requires the shutter sound. They actually rejected the first version of my video streaming App because the recording beep was missing.

Shutter sound is required by law in many countries.

How do those laws address devices without the capability to produce sound?

By forbidding them, most likely.

So the law mandates a speaker, and logic to convert data to audio, be bundled with every optical CCD?

The shutter sound can just be a beep as far as I know. One digital camera I bought for dirt cheap did that, presumably to cut costs.

Many countries? South Korea is the only one I can find a source for online. In Japan it appears to only be a voluntary choice among device manufacturers.

https://www.privacyinternational.org/reports/south-korea/ii-...

How about Ukraine?

"voluntary" choice in Japan is basically the regulators telling the carriers that if they don't do it they'll have to regulate. From the carrier's point of view, it's a matter of doing it now in friendly terms, or doing it tomorrow with the regulators on their back.

That was my thinking as well.

I wonder how many of the people cheering this are also the ones horrified by Google Glass because someone might disable the recording light.

I don't know about 'cheering' it, but as a hack, it did put a smile on my face.

This is a really cool solution to a problem that really seems like it shouldn't exist.

It's all relative. There are probably a lot of subway riding Japanese ladies that would argue that this problem really really should exist.

How do you figure? The same laws don't apply to digital cameras which come on all shapes and sizes.

When you are holding a camera, the intent is somewhat obvious. When you are holding a phone, not so much. That's the real separation.

Cameras come in all different shapes and sizes. I can get cameras that look like cellphones. I can even get keychain cameras for $4 off eBay and put them in my shoes. Set them to video and shoot hours of up skirt shots.

The law does nothing to stop people who want to take pictures without you knowing they're doing it. Anyone who wants to will. The law is pointless

No, it is not pointless.

The point of this law is to create the perception that the authorities are doing something about the perceived epidemic of upskirt photography.

The same authorities also erect signs next to escalators warning people that upskirt photography is a crime. They serve the same purpose: to make escalator-riding ladies feel that the authorities are watching out for them.

Don't knock it. It works.

I'm sorry, but I think if you buy that argument, your priorities are totally out of whack.

Putting legal restraints on someone else's technology because a very small number of people were subjected to mildly embarrassing/uncomfortable situations is ridiculous.

Privacy concerns like the right not to be photographed are not just about minor nuisances. People who are victims of stalking, violence, harassment and so on, deserve to be alerted if someone is trying to photograph them.

For example, imagine you're in witness protection and some random person snaps your pic and posts it online. Some face scanning thing finds the pic and it clues in the bad guys to your location. Now you're dead because someone didn't respect your privacy.

>People who are victims of stalking, violence, harassment and so on, deserve to be alerted if someone is trying to photograph them.

Why does that imply that it's OK to dictate how I'm allowed to use my technology? I'd say everyone's right to own and control their own devices trumps a few people's right to feel a little better about all the dozens of scary icky boogy men hanging out on the train.

>Now you're dead because someone didn't respect your privacy.

Which is a completely separate issue from legally requiring someone's device to follow some ridiculous rule invented because of a negligible edge case.

Do you really believe that requiring a camera to make a noise will actually protect anyone's privacy? People can always disable the speaker or do illegal hacks to the device. The only thing this law does is set a terrible precedent of allowing the government to control people's electronic devices.

People can always disable the speaker or do illegal hacks to the device

In the example scenario I gave, the biggest threat to a person's privacy was not hacker types, but just everyday people who post photos online. I think it's pretty self-evident that the majority of people would not modify their device in this way, even if they could.

Why does that imply it's OK to dictate how I'm allowed to use my technology

Even the most freedom-loving libertarians among us generally concede that your freedom doesn't extend to harming others. In the issue at hand we probably aren't even really talking about your freedom, per se, but simply how devices are manufactured. As you mentioned, no one can really stop you from modding a device, anyway.

By the way, you might want to try flipping your own reasoning around, and thinking about what a minor inconvenience it is to hear the camera sound, so that people's privacy can be protected.

You don't need to be a hacker to download an android app that disables the sound illegally, or remove the speakers.

> Even the most freedom-loving libertarians among us generally concede that your freedom doesn't extend to harming others.

Do you really consider being able to take photos silently "harming others"?

Why don't we just make cameras on cell phones illegal? After all, your freedom to have a camera "doesn't extend to harming others."

The reason your argument is bullshit is that most people (including libertarians) don't support punishing people before they're proven guilty of a crime. You can certainly punish upskirt-shot-takers, if you want, but don't preemptively mix up literally every innocent person with a smartphone.

>no one can really stop you from modding a device, anyway

But they can and have made it illegal, so if I do modify my device in the way I like they can throw me in prison.

>thinking about what a minor inconvenience it is to hear the camera sound, so that people's privacy can be protected.

This is a completely false dichotomy. The camera sound is not protecting people's privacy to any significant degree. It has the much more significant effect of inconveniencing a huge number of people.

You also haven't addressed the fact that this sets up the precedent for the government controlling people's technology.

Do you really consider being able to take photos silently "harming others"?

In very specific circumstances it can be, for reasons I already described.

In your world where simple privacy-enhancing measures are to be vociferously opposed should they cause any inconvenience whatsoever, I hope you never have enemies that you need to keep privacy from.

Are you arguing that it's impossible for any law to increase utility for a small group of people while decreasing utility for a much larger group of people? Or are you arguing that one group's utility is more important than other group's?

Why? What do you do if you notice someone taking a picture of you? Hearing the sound doesn't solve any problems.

After all, there must be a reason that there's even A SIGN for it!

http://main.makeuseoflimited.netdna-cdn.com/wp-content/uploa...

I don't think it's that hard to understand why they might have done it this way, is it? Privacy immediately comes to mind.

The front-facing camera doesn't have an indicator light, so this sound is the only thing preventing an app from stealthily capturing a photo or video recording of you while using it.

I'd imagine analysis of your emotional reaction to some stimuli (gameplay elements, advertisements, whatever) would be fairly valuable.

How is this possible? Doing ANC would require the sound to be played at the exact same microsecond as the target sound.

I would guess that the sounds are both enqueued, and then playback of both actually starts slightly later, perhaps when the audio hardware indicates that it's ready to start accepting data.

VERY low audio latency on iOS. Its not android

Closer to exact same millisecond. 44.1 kHz sampling rate + 64(ish)-sample buffer granularity = ~1 millisecond.

Even that is an overly harsh requirement. While being close does not completely remove the sound but still does severly reduce its volume:

http://www.wolframalpha.com/input/?i=sin%28x%29+-+sin%28x-0....

No, not really. If you're off by a millisecond (the minimum, assuming 64-sample buffers and 64 kHz sampling rate), frequencies which are even multiples of 500 Hz will be nullified, those which are odd multiples of 500 Hz will be amplified, and the rest will fall somewhere between those extremes. (This is known as a "comb filter"; see [1] and [2].)

Your examples demonstrate the behavior of such filtering only for frequencies much less than 500 Hz, which will indeed be attenuated. However, a camera "click" sound, being both brief and noisy, contains lots of high-frequency content which will be, on the whole, preserved.

In fact, assuming the "click" sound can be approximated by white noise, its total energy will be doubled by such filtering!

So yes, you do need to play the sounds within the same millisecond.

[1] http://en.wikipedia.org/wiki/Comb_filter

[2] http://en.wikipedia.org/wiki/File:Comb_filter_response_ff_ne...

Barely related, but it's surprising how often DSLR newbies show up on photography forums asking how to disable the shutter sound on their cameras.

Is this how noise-cancelling headphones work?

Not sure, but it's how a lot of karaoke tracks are made.

And if an artist releases instrumental or a capella versions of their track, you can usually use this to get the other. Only works if they're exactly the same as the original of course.

Another trick is to invert one of the stereo channels and add it to the other one: this eliminates everything that was mixed in with neutral pan. That's typically where the voice is. It will also remove e.g the drum kick, but this can be salvaged with a low-pass filter. Note that you end up with a mono track.

While on the subject of these tricks -- disconnect the ground from the audio out, and tie the speaker grounds together. This causes the speakers to use each other as ground, which in effect causes the middle voice to cancel out.

I used that trick to get a cheap rear channel from my thrift store stereo back in my high school days.

That's really interesting. I never knew how they did that. Canceling out the frequencies of the voice makes complete sense.

Yes. They have a microphone and a circuit that inverts that input and mixes it into the recording.

That's not really what happens in noise-cancelling headphones. The transforms required are fairly complex, simple mixing is a long way from what is required to achieve good results.

The transforms aren't complex... They're inverted. What's complex is getting the timing right (can only occur at a fixed distance from the ear so they can delay the generated canceling waves appropriately).

It's just wave addition. -1 + 1, occurring at the same time, is 0.

> The transforms aren't complex... They're inverted.

Again, It's not that simple. Most ANC headphones use a digital feed-forward control system using a variant of the LMS algorithm to provide coefficients to an adaptive FIR filter(s). Generally you also have to apply additional filters to model the loudspeaker / system response. Better systems will use a hybrid analog/digital approach, either way, there is a lot more to it than 'invert the mic signal and add'.

The reason that ANC headphones didn't really exist until recently is that sufficiently high performance yet low power DSPs were needed to perform the necessary computations.

Thanks for the correction. I assume that the simple

  v(t) + -1*v(t) = 0

approach is unworkable because you can't generate the canceling signal (-1 * v(t)) fast enough? By the time you have received it, amplified it, and played it back, it's too late? So you need a predictive approach.

It's more that sound waves aren't simple 1D sine waves varying over time. Sound is a 3D pressure field varying over time. A single microphone on the outside of the can doesn't give you a full picture of what noise is entering the inside of the headphone. The nature of the noise, the headphone fit on the user's head, even the shape of the user's ears can all influence what the noise field looks like inside the headphones. ANC headphones use 1-3 microphones on the outside and 1 or more microphones inside the can. The DSP makes a guess as to what it should do based on the signal from the outside microphones, then has to make corrections based on what the internal microphones hear, all of this while filtering out your music signal (which the microphones also pick up) so it knows what is noise and what isn't. This is why the system can't be instantaneous, the overall system response is time varying, so the correction filters have to be adaptive. It's also why they do a really good job at blocking continuous noise that they can zero in on an ideal correction for over time, e.g. aircraft cabin noise, but don't do a great job with 'spiky' sounds, like speech.

Thanks. I have an EE background, but I'm not familiar with the design considerations around these systems.

Thanks for the info, I didn’t realise the tech was mor advanced than my understanding of it.

Everyone is getting really excited because they think this is how it works, but no, not exactly.

The shutter sound comes from the same speaker as the anti-shutter sound. The phone is mixing the tracks together and playing nothing.

It's not like both sounds are played and they neutralize each other as sound waves.

Since it would have more general applicability, I am curious how effective could the noise-cancelling-like method could be? What would be the constraints on its effectiveness?

It's the same process that would happen if you actually played both sounds. The superposition is just happening in software instead of air.

Inverted sound waves can cancel each other in air, I've heard (or not heard) the effect with my own ears.

Right, but for any point source this is effect is going to vary spatially. That's why you can't make one speaker totally cancel out another speaker over a whole room.

Sure, but my point is that there is only one speaker involved so the cancellation happens in the electronics, before any sound is made.

It's interesting to think of 'cancellation' in different mediums. Waves in physical space. Radio in electromagnetism. And now 'computed' waves cancel each other too.

Hilarity from the comments: I wish I could upvote twice: once for the inverted-cancelling hack, and once for answering your own question, just to counteract anyone daft enough to downvote you for that. – Daniel Earwicker 1 hour ago

i think that was aimed at me. i said in a now deleted comment:

> Wow! Even though I know it's allowed, some coolness points deducted for posting the question yourself :-). I'd definitely do the same though. I'd be stopping random people in the street telling them the hack!

i know posting and answering your own questions is encouraged on SO, it was just a joke!

It looks like he posted it AND answered it at the same time though, which is really weird.

Especially weird considering the hack is totally unnecessary. You can take a picture without making a shutter sound using AVFoundation.

There's a checkbox at the bottom of the "Ask" screen that lets you write your answer before posting the question. Makes it easier to document a piece of knowledge if you don't have a blog to post it on.

http://stackoverflow.com/help/self-answer

Awesome hack! If anyone wants try it out and play around, here's a demo project: https://github.com/vpdn/SilentPhotoCaptureDemo

Another trick is to use a dummy cord. Use a broken headset and cut off the jack. Plug that into the phone.

Diverts sound to headset which doesn't exist. Or just put on a working set of headphones

Apple owns the copyright of the shutter sound.

That's enough to reject an app using this trick.

I guess the app could read the shutter audio file and invert it on the fly, it doesn't need to ship with the inverted sound upfront. As a bonus it would likely work even if future OS updates changed the sound (well, unless they moved the file so it would no longer be found)

On Android you can record without the user knowing which is way cooler.

Is that really true?

Only if you side load apps and give full permissions.

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