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| The Following 5 Users Say Thank You to aquasq For This Useful Post: | ||
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2012-07-20
, 07:22
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Posts: 1,808 |
Thanked: 4,272 times |
Joined on Feb 2011
@ Germany
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#2
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I think the whole audio processing is done by the pulseaudio and various plugins. Still haven't researched on this topic though.
One thing I'm almost 100% sure is that the actual GSM encoding of the audio (GSM voice codec) is implemented on the GSM chip. Meaning if you somehow manage to feed it with non-voice data (e.g. text or any form of encrypted data) it will still be processed as pure audio -> compressed with a lossy codec -> you will decode garbage at the receiving end.
One thing I'm almost 100% sure is that the actual GSM encoding of the audio (GSM voice codec) is implemented on the GSM chip. Meaning if you somehow manage to feed it with non-voice data (e.g. text or any form of encrypted data) it will still be processed as pure audio -> compressed with a lossy codec -> you will decode garbage at the receiving end.
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2012-07-20
, 17:49
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Posts: 4 |
Thanked: 8 times |
Joined on Jul 2012
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#3
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Now that is very interesting. I suppose the codec on the gsm chip is closed like the rest of the firmware and there is no way to alter it or force unmodifed streams over the air.
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2012-07-20
, 20:39
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Posts: 1,808 |
Thanked: 4,272 times |
Joined on Feb 2011
@ Germany
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#4
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well if somehow you managed to do that then it wouldn't be GSM anymore would it? 
this is like saying you use SMTP to send a raw HTML page and still expect the server to handle it
this is like saying you use SMTP to send a raw HTML page and still expect the server to handle it
| The Following User Says Thank You to reinob For This Useful Post: | ||
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2012-07-27
, 05:32
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Posts: 4 |
Thanked: 8 times |
Joined on Jul 2012
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#5
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Yes, I suppose you're right about that. But this is the point of having a custom codec/firmware, anyway - to be able to utilize GSM for other purposes. But without a way to capture and modify the encoded audio frames before the phone sends them to the tower, I guess this isn't feasible, except for phonetic trans-coding type solutions that require very robust encoding to overcome lossy compression and filters.
Last edited by aquasq; 2012-07-27 at 05:45.
Last edited by aquasq; 2012-07-27 at 05:45.
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2012-07-27
, 06:09
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Posts: 381 |
Thanked: 336 times |
Joined on Jan 2011
@ Stockholm, Sweden
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#6
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Originally Posted by aquasq
It is good that the gsm part is closed, if it had been open then it would have allowed for a lot of stuff that noone wants, like stealing another phones identity and such stuff.
Yes, I suppose you're right about that. But this is the point of having a custom codec/firmware, anyway - to be able to utilize GSM for other purposes. But without a way to capture and modify the encoded audio frames before the phone sends them to the tower, I guess this isn't feasible, except for phonetic trans-coding type solutions that require very robust encoding to overcome lossy compression and filters.
But, maybe you could try to code and decode the data as tones with different frequencies?
__________________
Deskypplet , a desktop for N900 *RIP*
Deskypplet , a desktop for N900 *RIP*
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2012-07-28
, 15:05
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Posts: 8 |
Thanked: 17 times |
Joined on Apr 2012
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#7
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Originally Posted by aquasq
This is exactly what dialup internet modems do.
... Maybe I want to send some text or data as "audio" because I don't have data or SMS service. This can be done in the drivers for the speaker and receiver? Or some place else?
http://en.wikipedia.org/wiki/Dial-up_Internet_access
I'm pretty sure you can do most of what you want. There's a voicemail app (I don't remember what it's called) and there's a desktop widget that can record calls (it's called recaller). Their sources might be a good place to start.
| The Following User Says Thank You to briggers For This Useful Post: | ||
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2012-07-28
, 15:20
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Posts: 1,625 |
Thanked: 998 times |
Joined on Aug 2010
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#8
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Originally Posted by aquasq
what's wrong with your volume rocker?
[...]
Suppose I wanted to do some kind of processing to the audio before it gets sent over the air. To increase volume, get rid of background noise[...]
my understanding is that NOKIA already does an awesome job with sound Quality; hope to do a better job then that?
Originally Posted by aquasq
briggers' link to analogue dial-up would be a complicated way to do that, but, fundamentally, isn't that what 2G does as well?
Maybe I want to send some text or data as "audio" because I don't have data or SMS service. [...]
dial-up won't work unless you are connected to a "dial-in" service and therefore short of indeed encrypting your whole comm., if 2G is not allowed or available, dial-up most likely won't work neither
Originally Posted by aquasq
strikes me as a very trollish idea...
Thank you
__________________
information is a necessary though no sufficient condition to rationality...
information is a necessary though no sufficient condition to rationality...
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2012-07-28
, 16:50
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Posts: 5,028 |
Thanked: 8,613 times |
Joined on Mar 2011
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#9
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Originally Posted by electroaudio
What? You think that security through obscurity is really effective?
It is good that the gsm part is closed, if it had been open then it would have allowed for a lot of stuff that noone wants, like stealing another phones identity and such stuff
The things You've mentioned are clearly possible now, unfortunately, and *wouldn't* be possible if GSM part would be Open worldwide. Your argumentation is like one guy few years ago, that tried to advocate closed (payware) DNS solutions as "more secure than Open equivalents".
/Estel
__________________
N900's aluminum backcover / body replacement
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N900's HDMI-Out
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Camera cover MOD
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Measure battery's real capacity on-device
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TrueCrypt 7.1 | ereswap | bnf
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Hardware's mods research is costly. To support my work, please consider donating. Thank You!
N900's aluminum backcover / body replacement
-
N900's HDMI-Out
-
Camera cover MOD
-
Measure battery's real capacity on-device
-
TrueCrypt 7.1 | ereswap | bnf
-
Hardware's mods research is costly. To support my work, please consider donating. Thank You!
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2012-07-29
, 10:09
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Posts: 4 |
Thanked: 8 times |
Joined on Jul 2012
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#10
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Originally Posted by electroaudio
I don't think stealing phones would be possible, unless the service providers just ignored it. Interference from non standards compliant phones, yes.
It is good that the gsm part is closed, if it had been open then it would have allowed for a lot of stuff that noone wants, like stealing another phones identity and such stuff.
Originally Posted by electroaudio
I think this is the only way to do it without an open radio. But it is non trivial and the data needs to be encoded so that the GSM codec and any transcoding by the network won't corrupt it. This makes it obvious to the network that something fishy is going on.
But, maybe you could try to code and decode the data as tones with different frequencies?
Originally Posted by briggers
Thank you for that. I have recorder but didn't know about the voicemail app
Originally Posted by misterc
Do I have to? Or did someone else do this already? Does the n900 support AMR-WB? Why have open source at all?
what's wrong with your volume rocker?
my understanding is that NOKIA already does an awesome job with sound Quality; hope to do a better job then that?
Originally Posted by misterc
I don't understand. I would still be sending a digital signal. It just would be a data stream chopped up and inserted into audio frames so that the network would let it through over voice. 2G/3G/3.5G/4G shouldn't matter.
briggers' link to analogue dial-up would be a complicated way to do that, but, fundamentally, isn't that what 2G does as well?
dial-up won't work unless you are connected to a "dial-in" service and therefore short of indeed encrypting your whole comm., if 2G is not allowed or available, dial-up most likely won't work neither
Originally Posted by misterc
Many people are interested in this idea. Why do you think it is trollish?
strikes me as a very trollish idea...
Originally Posted by Estel
Exactly. Security through obscurity is only effective for the telecoms. Personally I would like to know if someone has a way to eavesdrop on my calls or if someone is stealing my credits. I think it's a good idea for those of us making the calls.
What? You think that security through obscurity is really effective?
The things You've mentioned are clearly possible now, unfortunately, and *wouldn't* be possible if GSM part would be Open worldwide. Your argumentation is like one guy few years ago, that tried to advocate closed (payware) DNS solutions as "more secure than Open equivalents".
Last edited by aquasq; 2012-07-29 at 10:37.
| The Following User Says Thank You to aquasq For This Useful Post: | ||
Please excuse me if I'm posting this in the wrong forum. I thought to make this post in the multimedia forum but I decided to write here since I am interested specifically in the n900. Although my question is very general and beginner level. So excuse me if I'm in the wrong place
I am interested in learning more about how the audio system works on this phone. I looked over the information at the Developers' Guide (http://wiki.maemo.org/Documentation/...udio_Subsystem) but I am new to this and confused already.
As far as I understand, when making a voice call, there is the receiver/microphone that receives audio from whomever is talking. There are drivers for this piece of hardware and these drivers let other parts of the phone .. hardware or software communicate with the receiver. And there is a speaker to listen from, and also drivers for this. What happens next? If I make a voice call, I am speaking into the receiver->receiver drivers-> XYZ -> operating system -> XYZ -> encoded audio frames go to GSM radio -> GSM radio firmware -> over the air to cellular network, is that right?
Suppose I wanted to do some kind of processing to the audio before it gets sent over the air. To increase volume, get rid of background noise, encryption, or whatever. Maybe I want to send some text or data as "audio" because I don't have data or SMS service. This can be done in the drivers for the speaker and receiver? Or some place else?
Thank you