Alban’s blog

We bought a M-Audio Delta 66 last year to complete our multi-track captation system. We’re working for a long time with M-Audio sound cards and especially with Delta 44 ones. So we were a bit surprised when we discovered that the M-Audio Delta 66 revision E wasn’t supported by the alsa project.

To retransmit in live the Amparanoia’s gig at Esperanzah! festival, we need a additional 4 tracks sound card. On sunday, the challenge was to configure our Delta 66.

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Le concert d’Amparanoia sera en direct dimanche soir à 22h sur les ondes de Radio Esperanzah!.

Il nous reste juste … à trouver des micros d’ambiance, à faire câbler le tout, à trouver une petite place en backstage et à remettre en place le disposition inauguré pour Radio Bemba l’année dernière.

Mêmes ingrédients : icecast, ices2, quelques M-Audio et beaucoup de Ogg Au travail et à demain soir.

One of the challenges for Radio Esperanzah 2007 was broadcasting in live the Monday special event with Manu Chao Radio Bemba.

On the stage, outputs were the same than for the other lives : stereo lines with the frontstage, two lines from the ambiant microphones.

No way for us to mix these 4 signals before sending them to our studio. Firstly, no space in the loaded sound setup : two huge Midas mixers are installed for the evening. Our small setup (PC tower, 1U compressor/limiter/cables) have just a place under one of mixers. Secondly, .. we don’t have the required mixer. A small Behringher UB isn’t the right device for the job.

So the main part of the problem was sending to our studio the 4 captured lines.

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The Radio Esperanzah! streaming is based on a master icecast2 and a set of public relay icecast2. The master icecast2 is up for a week with a local fallback ogg file. It makes possible tests from every radio partner.

By setting the first public relay yesterday evening, we experienced a strange behavior of this relay icecast2. Any client player was kick off after nearly 30 seconds. The server log claims that the “Client [...] has fallen too far behind, removing”. Very strange for a 100kbps stream read via a 20Mbps DSL line ..

I’ve found the problem with .. wget. A simple wget on the master stream retrieved data at 600kpbs 8-/

In fact, the icecast2 fallback with a local file doesn’t manage the client bandwidth. With a “real” client (a music player), it doesn’t make trouble. The client is limited by .. the sound card. But any client which doesn’t “play” music (a relay server, a transcoder, etc …), the icecast2 server sends data as fast as possible.

In this case, a icecast2 relay fills any client queue in few seconds and kicks off clients.

We experienced the same trouble with streamTranscoder. It received the ogg stream at … 600kpbs and didn’t manage to create an mp3 stream as fast. We expected a streamTranscoder bug .. but in fact, it was a stream problem.

We replace the local file mount in icecast2 by a ezstream instance. All is fine now.