[PD] wireless audio from Pd to PA system (katja)

Tue Mar 5 00:41:05 CET 2013

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

On Fri, Mar 1, 2013 at 9:34 PM, Phil Stone <pkstone at ucdavis.edu> wrote:

>  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 at 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 at gmail.com>
>> *To:* Antoine Villeret <antoine.villeret at gmail.com>
>> *Cc:* richard duckworth <richduckworth at yahoo.com>; "pd-list at iem.at" <
>> pd-list at 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 at 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 at 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
>>
>>
>> --
>> do it yourself
>> http://antoine.villeret.free.fr
>>
>>
>> 2013/2/28 richard duckworth <richduckworth at yahoo.com>
>>
>>   Hi Katja
>> one 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.
>>
>>  http://www.thomann.de/ie/cat.html?gf=wireless_for_guitar_bass&oa=pra
>>
>>
>>
>> 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 at gmail.com>
>> Subject: [PD] wireless audio from Pd to PA system
>> To: pd-list <pd-list at iem.at>
>> Message-ID:
>>     <CAFY0eapPSKfw+gVaxuTr7exHqLiG+pTdu8Rk6SNTraLiys2Msg at 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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