[PD-announce] Zhong Shuo | Long March Space, Beijing

[Iain Mott]

Stage 1 of the Zhong Shuo sound installation project by Iain Mott and Ding
Jie opened at the Long March Space in Beijing on 20 August.

Please visit www.reverberant.com/cw

There are links on this page for live audio, images and text

Please note, due to some ISP funny business, the IP address of the local
streaming server needs to reset on the hour, every hour Beijing time - so
if it's not working please try again later. Streaming runs 24H.

The site will be updated regularly so please visit again. Next stop
Yanchuan County, then Kunming.

Will paste a draft technical description at the end which may be of
interest to the list - best read after looking at the site.

cheers, Iain

________
Iain Mott
www.reverberant.com
China Mobile: 1352 045 6942


Zhong Shuo - Technical Description

A modified telephone in the kiosk and computer interface (both designed
and built by Jim Sosnin) enables the computer to record speech and play
voice prompts on the receiver earpiece. The interface also connects to the
games port of a sound card and produces control voltages in response to
MIDI messages from the computer (using a PIC chip) to control the ringer
of the phone. Control voltages sent in the opposite direction, from the
phone, are converted to MIDI messages by the interface and sent to the
input of the games port. These messages allow software on the computer to
detect when the receiver is on or off-hook. A second output channel of
audio from the computer is connected to a mono amplifier which sends sound
to an outdoor speaker at the rear of the pond.

The computer at each site uses (will use) the Linux operating system.
Miller Puckette's graphical sound language 'Pd' performs audio input and
output tasks and a variety of other operations including MIDI processing.
My own extensions to Pd written in the C language interface with a
database called PostgreSQL. When the receiver is lifted, Pd begins
playback to the earpiece channel a prerecorded message repeating the
questions in Chinese and prompting the participant to speak after a beep.
If the receiver remains off hook Pd begins to record the voice direct to
the hard disk. As it records it runs simple 'voice segmentation' routines
to determine where phrase-bursts occur and writes this data to the
database. At present in Beijing however, this information is not being
used, but may be used in the future. Once the receiver is replaced, the
recording is stopped and information about the recording, including the
file name, date, time and duration is written to the database in special
tables corresponding to the local site (ie. the Beijing installation
writes this data to the 'Beijing' tables). Recordings are compressed using
the 'speex' format. If the recording is less than seven seconds long, it
is rejected. If a speaker talks for 11 minutes and 45 seconds (15 seconds
less than the maximum length of 10 minutes), Pd sends a warning voice
message to the earpiece informing the speaker they have 15 seconds to
finish. If the speaker continues to speak for more than 15 seconds a
second message informs the them that the recording has finished and to
please hang up the receiver. All recordings longer than 7 seconds are
acknowledged by a  voice message played over the garden speaker.

At all times, recorded story files are selected, edited and played back by
the local computer  in an interwoven fashion (the volume of this playback
is however lowered slightly during recording to minimise leakage of other
recordings). Selection and playback is performed by an extension to Pd
that attempts to fill a particular length of time with edited stories.
This is currently set to 15 minutes and the number of stories/voices it
plays back 'simultaneously' in interwoven or cross-faded form is set to 3.
Stories are fragmented into semi-random chunks, usually around 10-15
seconds in length and are played in their original temporal sequence.
These fragment are given additional 'lead-in' and 'lead-out' durations
which are sounded during crossfades and allow the listener to reacquaint
themselves to a given speaker returning to his or her story. The playback
process begins playing a given story, as the end of the first fragment
approaches, it begins to crossfade the voice with that of a new speaker.
It then does the same with a third voice (and so on if more that 3
simultaneous speakers has been specified). This continues until a story is
exhausted whereupon a new story is added to the queue. Once the 15 minutes
of stories has been played, the entire process begins again.

As this project develops and new installations are created, the playback
process will select stories from all sites established. This will be done
with an even distribution of sites in the resulting playback.

Each installation will have its own computer and the system on each will
be almost identical. The Beijing machine is slightly different in that it
streams its audio output (the edited stories and not the voice prompts) to
the Internet. These streams can be accessed at www.reverberant.com/cw.
Streaming runs for 24 hours a day at present, but in future there will be
some downtime as file transfers  take place between installations.
Streaming is achieved with the 'shoutcast~' Pd external which is
configured to send an MP3 stream to a local (on the Beijing machine)
'Icecast' server. The signal from this is then relayed to a commercial
'Shoutcast' service to enable a broader public access (more simultaneous
connections).

The other difference with the Beijing machine is that it will act to
initiate synchronisation of content between installations. As audio
material, and database material associated with it, is shared between the
machines, the Beijing machine will initiate a process of first collecting
data from each machine, then redistributing to other machines that need
it. This will be performed at night, once daily. Synchronisation is
achieved using a variety of 'shell' scripts but principally the efficient
Linux data transfer tool 'rsync' over a secure network connection (ssh).