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Topic: IP-lossless transmission of 24bit audio (Read 5570 times) previous topic - next topic
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IP-lossless transmission of 24bit audio

Hi experts here,

maybe someone could give me an interesting hint.

Here is my project:

I want to make a  measurement station that provides 24bit - 48Khz samples wireless and solar powered. Input is a calibrated USB measurement microphone
Ideally the transmission distance should be up to 50 m. The codec used for the transmission must be lossless and keep the 24 bit fidelity
The solution must ideally stream 24-hours/365days.
Latency is irrelevant, I even could afford several seconds...

To my knowledge there is nothing existing ready-made on the market.
I am looking for a solution running on a solar powered Raspberry Pi with a good wifi antenna as the sender.


On the receiver side, I would have a linux driven notebook and a software sound pressure level meter expecting to receive the 24bit - 48Khz samples as an input.

I have been using LINUX for several years as a user, but am not experienced in audio processing, and -to be honest- I wasn't even able to set-up Jack correctly without producing a huge mess. 
but, I promise, I will try better...

What could be the software approach?
any ideas?

IP-lossless transmission of 24bit audio

Reply #1 –
The PI uses a lot of power (its not a very efficient board by modern standards), so you'll need a fairly large battery and solar array:

http://www.voltaicsystems.com/blog/powerin...om-solar-power/

A microcontroller would be more power efficient, but setting that up with wifi would certainly be more complex.  Alternatively you could probably buy a ready made device that did this using a wireless mic or wireless data acquisition device.  What kind of dynamic range do you need for your measurement?

IP-lossless transmission of 24bit audio

Reply #2 –
Does it have to be wireless over such a short distance?  Ethernet easily goes 50m (100m max on a single link).  Combine that with a POE injector/extractor pair and you solve your power problems as well.

IP-lossless transmission of 24bit audio

Reply #3 –
Quote from: saratoga on
The PI uses a lot of power (its not a very efficient board by modern standards), so you'll need a fairly large battery and solar array:

http://www.voltaicsystems.com/blog/powerin...om-solar-power/

A microcontroller would be more power efficient, but setting that up with wifi would certainly be more complex.  Alternatively you could probably buy a ready made device that did this using a wireless mic or wireless data acquisition device.  What kind of dynamic range do you need for your measurement?


You are right: the dynamic range is the crucial point. At least 80dB(a). 24 bit 44.100 (mono) uncompressed (or at least lossless compressed) is my target.
The best woud be a dedicated audio transmitter, but I could not find any affordable.

IP-lossless transmission of 24bit audio

Reply #4 –
You do know that lossy compression can give greater dynamic range than 24 bit uncompressed?

IP-lossless transmission of 24bit audio

Reply #5 –
Quote from: rin67630 on
You are right: the dynamic range is the crucial point. At least 80dB(a). 24 bit 44.100 (mono) uncompressed (or at least lossless compressed) is my target.


That is not very much by audio standards.  I would think a commercial wireless system should do that.  If you can't find one cheap enough, another option would be to just get a cheap android smartphone and a battery pack.

IP-lossless transmission of 24bit audio

Reply #6 –
Quote from: pdq on
You do know that lossy compression can give greater dynamic range than 24 bit uncompressed?


Now I know it, thanks.
Indeed the fidelity isn't really the concern, since my SPL application will have an (A) filter that kills everything above 10Khz and reduces drastically the sensitivity below 200 Hz.

The only important thing is that the dynamic must be maintained.

IP-lossless transmission of 24bit audio

Reply #7 –
One solution would be to do the filtering and SPL calculation on the embedded side and just sent the result. You could save power by buffering up long periods of time, obviously depending on what your application might be.

You could also use WavPack lossy. It will easily compress 24-bit audio to 4-bit (for example) and preserve all the dynamic range, and doesn't require a lot of CPU for encoding. The Linux package builds for Pi without issue (don't use the package for Raspbian because it's old and even has encoder bugs).

IP-lossless transmission of 24bit audio

Reply #8 –
Quote from: saratoga on
Quote from: rin67630 on
You are right: the dynamic range is the crucial point. At least 80dB(a). 24 bit 44.100 (mono) uncompressed (or at least lossless compressed) is my target.


That is not very much by audio standards.  I would think a commercial wireless system should do that.  If you can't find one cheap enough, another option would be to just get a cheap android smartphone and a battery pack.


I am a bit reluctant about wireless mics, I think they might have frequently got some kind of dynamic compression, arent't them?

The solution with an android smartphone is sexy. It has everything on board and does not require a lot of power.
The application "wireless mic" -although having a lag of up to 4 seconds, which is OK for me- seems to do a good job.
But it surely heavily depend on the make of the smartphone, whether the microphone input's dynamic is linear or not, I fear it is frequently optimized with compression chips.
I would love to use a USB microphone, but then the OTG port will not allow powering the smartphone any more.

Do someone know an old smartphone/small tablet that allows OTG and has a discrete power socket?

IP-lossless transmission of 24bit audio

Reply #9 –
Quote from: rin67630 on
But it surely heavily depend on the make of the smartphone, whether the microphone input's dynamic is linear or not, I fear it is frequently optimized with compression chips.


I would not use the built in microphone, instead I would use your own microphone hooked up to the device's mic jack.

Quote from: rin67630 on
I would love to use a USB microphone, but then the OTG port will not allow powering the smartphone any more.


You can probably work around this, but there is no reason to use a USB microphone, just use a good analog one. 

IP-lossless transmission of 24bit audio

Reply #10 –
Quote from: saratoga on
Quote from: rin67630 on
But it surely heavily depend on the make of the smartphone, whether the microphone input's dynamic is linear or not, I fear it is frequently optimized with compression chips.


I would not use the built in microphone, instead I would use your own microphone hooked up to the device's mic jack.

Quote from: rin67630 on
I would love to use a USB microphone, but then the OTG port will not allow powering the smartphone any more.


You can probably work around this, but there is no reason to use a USB microphone, just use a good analog one.


I don't know what circuitry the smartphone mic input has. If it has a level optimization and -i think most will have one-, then I've lost.

IP-lossless transmission of 24bit audio

Reply #12 –
See section 5.4...
https://static.googleusercontent.com/media/...android-cdd.pdf
...it's mandatory to switch off all the processing when doing voice recognition - so the capacity to do what you want probably exists in many Android devices. The linearity requirements might not be good enough for you though.

Cheers,
David.

IP-lossless transmission of 24bit audio

Reply #13 –
Quote from: rin67630 on
...
Do someone know an old smartphone/small tablet that allows OTG and has a discrete power socket?


All phones that I know of have a microphone input on the headphone socket. I don't know if this input is accessible from an audio app.

Edit: I just tried this with my smartphone. It works. (Headset microphone, audio spectrum analyser app.)
Regards,
   Don Hills
"People hear what they see." - Doris Day