Sending Pd-audio over Wifi would have the advantage that no extra gear is needed at the transmitter side, simplifiying the setup of a wearable live performance computer. Therefore this would be the method of my preference, if it is possible at all.
This weekend I did some experiments with [udpsend~] and [udpreceive~] over Wifi. I soon found that using a wireless router makes little sense. Wifi is 'half duplex', meaning it can't send and receive at the same time, so the router is either receiving from one computer or sending to the other. A waste of time.
I learned about 'ad hoc networks', where computers can be paired via Wifi and talk to each other directly, without a router. Never knew about this before. What a cool option that is. Found a howto here:
https://help.ubuntu.com/community/WifiDocs/Adhoc
In ad hoc mode, latency is lower, although on average not as low as over cable, and with more fluctuation. Moreover, there was considerable packet loss, which did not happen in wired LAN. Therefore, tcp protocol should probably be used instead, to check for packet loss and eventually resend packets.
I found that [udpsend~] can not send packets of 64 samples. It seems that 256 samples is the minimum. Why? Maybe it is best to pack each signal vector in a list and use the [tcpsend] / [tcpreceive] combo instead.
A well-known issue with music streaming is clock drift, caused by the slightly different clock speeds between audio cards. This also happens when sending over a local network (wired or wireless). Clock drift is typically 0.0001 to 0.001 ratio of nominal sample rate. A small difference, but it causes one buffer to be skipped or duplicated once in a while. To compensate, the signal should be resampled to match the receiver's sample rate. This would not require a complicated interpolation scheme, but still it would probably need one or more new Pd classes. An interesting article about clock drift and possible solutions is here:
http://www.carot.de/Docs/AES_Tokyo.pdf
If further experiments are promising enough, I would try this board for the receiver:
https://www.olimex.com/Products/OLinuXino/A13/A13-OLinuXino-WIFI/
Otherwise, I would just be happy to have learned about ad hoc networks. This can come in handy for other purposes too, for example when synching Pd computers.
Katja
These Line 6 units are well respected in the electric bass world, especially considering their moderate price. I think bass players appreciate tight timing, and the low lag may be one reason these units are popular. Also, they have proven to be rugged enough to be "road-worthy". They can also model the hi-frequency lossiness of cords, though that seems of dubious value in your case.
Phil
On 3/1/13 12:24 PM, katja wrote:
Apparently, Line 6 managed to build a digital 2.4 GHz wireless with <4 ms latency, the Relay G30, G50 etc . They do not write it in the specs, but most users don't notice latency and when they do, their support is speaking of latency as low as that:
http://line6.com/support/thread/33898
This weekend I will do some WiFi experiments and see how fast it can go locally, using mrpeach udp and tcp classes. If it works, one could use a wireless router which has no other task than routing Pd audio, and the computer at the receiving end could be a cheap headless board with no other task than receiving Pd audio and converting it to analog. Together the receiving device could be the size of a weight-watcher's lunch box, while at the transmitter side the computer's built-in stuff is used. Maybe I'm a bit naive here, anyway I'll report results from experiments.
Katja
On Fri, Mar 1, 2013 at 2:14 PM, richard duckworth <richduckworth@yahoo.com> wrote:
OMG - that's really high! Maybe Tranz have a belt holder solution - they do look kind of bulky though! Maybe worth dropping them a line, see if they'll help the Pd community
Rich Duckworth
Lecturer in Music Technology
Department of Music
House 5
Trinity College
Dublin 2
Ireland
Tel 353 1 896 1500
"Digital?
Is that the thing where they take a good old sine wave and they chop it up into little bits?" --- Rupert Neve
From: katja <katjavetter@gmail.com>
To: Antoine Villeret <antoine.villeret@gmail.com>
Cc: richard duckworth <richduckworth@yahoo.com>; "pd-list@iem.at" <pd-list@iem.at>
Sent: Friday, 1 March 2013, 13:12
Subject: Re: [PD] wireless audio from Pd to PA system (katja)
Found more info about TI's PurePath wireless. Latency of wireless transmission is 768 samples minimum. Added to this must be the latencies of ad/da conversion.
http://e2e.ti.com/support/low_power_rf/f/382/t/110331.aspx
Forget about it, this concept is only useful for home entertainment.
Katja
On Fri, Mar 1, 2013 at 1:19 PM, katja <katjavetter@gmail.com> wrote:
Thanks everyone for your answers.
The case is unconventional because a stereo line signal must be sent from the computer. Professional wireless systems assume mic or instrument. Consumer systems do transmit stereo signal, but without bothering too much about latency.
Frankly, I did not expect the difficulty to find a good solution. Initially I wanted the wearable computer for a music video which is to be recorded live with sounds from natural objects. I bought the FM transmitter so my cameraman will be able to hear the music while he's filming. For this purpose it is ideal. Then I thought it would be good to use the computer in it's wearable mode for public performance. I figured that one of the many wireless solutions would suit the purpose, but didn't reckon with the unusual requirements.
Further searching brought me to a new technology 'PurePath' from Texas Instruments. It has a range comparable with WiFi (30m), while it seems to work with paired devices as in Bluetooth. I haven't seen consumer products with this technology, but development kits are available. A rather convincing demo is here:
http://www.youtube.com/watch?v=0YsnZQUfVGs
If this system can work with low latency it could be perfect for wireless Pd.
Katja
On Fri, Mar 1, 2013 at 11:41 AM, Antoine Villeret <antoine.villeret@gmail.com> wrote:
hello,
those are good for what they have been designed for and it depends on what you mean by "exellent sound quality"
I've made few tests on those few years ago and the bandwidth could be good enough to transmit guitar/bass signal but nothing else for me
+a
2013/2/28 richard duckworth <richduckworth@yahoo.com>
_______________________________________________Hi Katjaone of these would do it - check with Thomann tech support for gain issues (these are Instrument Level input) They should be fine however as active guitar pickups (like heavy style EMG pickups) output quite high levels. These type of wireless systems tend to be very rugged, have excellent sound quality and long battery life - and you'll want these things.
Rich Duckworth
Lecturer in Music Technology
Department of Music
House 5
Trinity College
Dublin 2
Ireland
Tel 353 1 896 1500
"Digital?
Is that the thing where they take a good old sine wave and they chop it up into little bits?" --- Rupert Neve
Message: 3
Date: Thu, 28 Feb 2013 11:53:43 +0100
From: katja <katjavetter@gmail.com>
Subject: [PD] wireless audio from Pd to PA system
To: pd-list <pd-list@iem.at>
Message-ID:
<CAFY0eapPSKfw+gVaxuTr7exHqLiG+pTdu8Rk6SNTraLiys2Msg@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
For a wearable live performance computer, I am looking into the
options of sending wireless audio from Pd to a PA sound system and
other listeners.
In a first experiment I've tried a Linex FM transmitter. Audio quality
is good enough, and FM transmitters do not introduce latency. This
option is cheap and flexible, as the signal can be received by simple
radio's, which are even built into cell phones and media players. I
would need to boost the transmission a bit to make it more reliable.
This will of course make the equipment illegal. Even then, the risk
that someone else is transmitting a stronger signal on the channel can
not be excluded.
Another option could be to send audio over Wifi. This would require
WLAN to be available, and one extra computer (with audio interface) as
a receiver. To avoid extra latency the audio should be sent
uncompressed, like [udpsend~] / [udpreceive~] can do it. This has the
risk of packet loss and serious dropouts.
I've been searching for 2.4 GHz wireless music receivers and found
things like this:
http://www.sitecom.com/en/wireless-music-streamer/wl-061/p/203. They
seem to act like external soundcards for your computer. In Linux
though I've never managed to properly connect multiple soundcards with
Pd (in OSX it's easy using the Aggregate Device Editor from Audio MIDI
Setup). Also I guess these devices introduce huge latency. With audio
over bluetooth headsets I've experienced latencies up to a second.
Does anyone use a satisfactory method in practice, to send audio from
Pd without wires?
Thanks,
Katja
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