Techie Bits

stereo_tool_700-3

A page to collect all the technical details about FXR, starting with a brain dump of the studio and aerial site components, showing the various bits of hardware / software used and where the signals go, mostly :)

fxr-technical-details.pdf

Open the PDF in a separate window and I’ll talk you through it..

Studio#1

The downstairs, main, basement or ‘inaccessible’ studio (depending on who you talk to!).

We have two PC’s: one plays out automated (aka sustainer) content using StationPlaylist Studio, is used for recording shows using Audacity and provides internet browser access courtesy of Firefox, all on Windows – that’s the blue box; the other provides live content play out using Rivendell, the audio stream endpoint for transmission using Darkice and Icecast and records our mandatory Ofcom log, all on Ubuntu Linux – that’s the orange one. We like diversity :)

Each PC can operate independently, with it’s own content store, and we try to ensure that the content varies between systems to avoid automated shows overlapping with live ones.

We have different data protection strategies in use for these machines: automation content is backed up to studio#2 nightly (see next slide), Rivendell content is stored on mirrored disks (RAID1). We used to have mirrored disks in the Automation PC but one has failed, and it’s useful to have the content elsewhere (see below).

The automation PC exports it’s content drive (M:) for other machines to access within the building. Likewise the Rivendell PC exports it’s content store (/var/snd), and a special import folder (/var/tmp/import) which provides content ingestion by simply copying files into this area where the Rivendell ‘rdimport’ application picks them up.

Both PCs have ESI Juli@ sound cards providing balanced audio connections to the studio mixing desk, a rather vintage MBI Series 12 made in Brighton around 1982..

Also attached to the desk are a pair of Thomann studio condenser microphones, with an external phantom power unit hand-crafted by Clive Garnham, a JB Systems CD 570 dual CD player and an Eltax HiFi tuner amp + speakers for monitoring. Finally (and not on the diagram), there is a headphone amplifier fed from the presenters output of the desk- bring your own ‘phones please!

Studio#2

The upstairs, small, preparation or accessible studio..

Similar in concept but with less kit in than studio#1, we have a single PC running Ubuntu Linux, with no sound cards – instead I’ve connected the USB port to the mixing desk’s ‘2 Track USB’ port for audio I/O. In order to have PC audio on a fader rather than directly feeding the mixer bus requires a ‘special hack cable’ from the 2TK /input/ connectors (where audio /out/ of the PC is available) to a fader channel. The main mix output is always fed to the 2TK output and back up the USB, so we can process on the PC.

Because this machine is used for many purposes and requires multiple audio applications to work simultaneously, the audio routing is more complex than studio#1; in particular we have retained Pulse audio (the default Ubuntu audio manager) to allow most applications to work without tinkering about, especially web browser audio, StationPlaylist Creator and other media players. Logically below Pulse audio and connected using the jack-connect optional drivers we have Jack Audio, which is required to support Rivendell and Darkice (and other professional audio applications eg: Ardour). Surprisingly this arrangement doesn’t collapse in a heap too often!

As per studio#1, we use Audacity for recording shows, editing content etc. Firefox for browsing the web and Rivendell for preparing and sometimes playing out live show content. Darkice and Icecast provide both our Ofcom recording and a stream endpoint for transmission.

Station Playlist Creator (a windows application) is installed under Wine, providing automation scheduling and content management for the play out engine in studio#1.

Those grey ‘disks’ you see are mounted from the machines in studio#1, in particular: we create a virtual ‘M:’ drive through Wine for StationPlaylist Creator, mapped to the real drive M: on the automation PC, so they have the same view of the content; we mount /var/snd from the Rivendell content store so that the Rivendell tools have access to audio files. We also mount /var/tmp/import from the Rivendell PC so new content can be easily ingested from local sources (such as CD rips, presenters USB storage devices, YouTube, etc.)

This PC provides a nightly backup for the Automation content store, using rsync to replicate the store to a local disk (/media/DATA/AUTOMATION_BACKUP). This disk is then exported using samba so other machines can access it, in particular the station Laptop which has our 2nd licensed copy of StationPlaylist Studio installed as a backup play out machine.

The mixer in this studio is a significantly newer, but smaller Citronic M8DSP made in China (and already obsolete according to the reseller, hence the weird link!). This provides phantom power for a pair of Thomann studio condenser microphones, and feeds a set of active speakers (sub woofer and desk pods) via the headphone socket for monitoring. Because this isn’t a broadcast mixer, it doesn’t have output muting when faders are lifted, so we ask that all presenters unplug the speakers and use headphones while on air to avoid echo or feedback.

To your left in studio#2 is a wall-mounted rack housing an American Audio DCD Pro 310 Dual CD player, and a Denon DN-X500 mixer which is presently used to mix the two CD channels into one (as there aren’t enough channels on the main mixer). It’s serious overkill but it was free.. cheers Clive :)

Other machines & remote access

All the studio PCs are connected to the building’s local area network (LAN), as are other machines in the office areas and personal machines that presenters bring in. With appropriate credentials, all these can access the automation content, the backup automation content, the Rivendell content and the Rivendell import folders, allowing content management from multiple locations.

For remote access we have an external gateway server running Untangle and OpenVPN that allows the technical team to remotely connect to the LAN and thus the PCs on it. By this means I can do most content management from home, and most importantly, our aerial site can access the studios for transmission streaming, speaking of which, slide #3…

Aerial site

At the Orwell Hotel we have our aerial (transmitter) site. For the curious, stand on the path that runs between the Hotel car park and Cash Converters and look at the flat roof of the hotel accommodation block – our aerial is the 1.5m white stick towards the rear of the roof.. in the white ‘shed’ towards the front of the roof is the hotel water tank, and our transmitting equipment. Note that our only environmental control is 500 gallons of water nearby that is unlikely to change temperature much!

The PC here provides three functions: collecting an audio stream from studio#1 or studio#2 via the Internet and an OpenVPN connection into the studio building LAN, processing (compressing) that audio stream for transmission and feeding processed audio back out to an Internet relay service for our Internet listeners.

Collecting the audio stream is VLC Media Player, which is controlled by the processing software StereoTool. I wrote a small Python web application called ‘Studio source switcher’ which runs on this PC to allow web browsers in the studio network to see which studio stream is active, and to change between them by sending commands to the processing software.

StereoTool (screenshot at the top of the page ’cause I love it!) applies automatic gain control (AGC), multi-band compression, FM broadcast equalisation, stereo encoding (into MultiPleX: MPX format) and adds Radio Data System (RDS) information – this is where the station name comes from on your car radio. The MPX signal is then connected via an ESI Juli@ soundcard running at 192kHz to the transmitter. StereoTool also provides a tap on this processing chain, just before the FM equalisation, connected to the on-board sound card where you can listen to it with headphones at the back of the PC and where other software can pick it up.

We use M3W to pick up this compressed audio, encode it into MP3 format using LAME and feed our Internet streaming provider Mixstream.

Finally we run Piraside to monitor the audio coming through and take remedial action if it fails (currently that’s just an email to me). Longer term I intend to fit this system with a hardware watchdog as it’s quite inaccessible in a roof area and has been known to lock up (thanks Windows XP).

Our transmitter is a Broadcast Warehouse TX50, the aerial co-axial lead has a mandatory Ofcom measurement coupler so they can check forward and reverse power levels, and finally the aerial is mounted on a 2m pole to put it just above the roof clutter.

The transmitter has it’s own MPX encoder built in, should we need to connect a local audio source (like a mobile phone headphone output) to maintain audio output while working on the PC.

So that’s all the bits – coming next the storage details.. TBC..

Phil.

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