What are the Audio-I/O-Libraries ?

The Audio-I/O-Libraries are a simple way to send uncompressed audio streams from one application to another. At the moment, both applications must run on the same PC.
The first Audio-I/O-Library (in_AudioIO.dll, written in March 2008) was a shared windows DLL, which could be loaded into Winamp, and acted as an audio-bridge between the author's Spectrum Lab and Winamp (see last chapter in this document). The purpose was to send an MP3-encoded audio stream from a radio receiver to the web, using Winamp + Oddcast for the audio streaming, and Spectrum Lab for the audio pre-processing.

The Audio-I/O bundle (consisting of the compiled binaries, the C sourcecodes, and the manual) can be downloaded from this site. But first, read the next chapter...

Disclaimer

 (Ok, I hate this paranoid stuff, but someone told me it's wise to have it here..)

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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Downloading and Installation

The Audio-I/O-Libraries, including the manual, the compiled binaries and the C sourcecode, can be downloaded from here:

http://freenet-homepage.de/dl4yhf/AudioIO/AudioIO.zip

(if the page has moved, ask your friendly search engine)

The "installation" is straightforward: Just unpack the compressed archive into a directory of your choice. In it, you will find (at least) the following files:

• manual/AudioIO_Manual.pdf : you guessed it, this is the manual. READ IT.

• in_AudioIO.dll : The first compiled Audio-I/O-Library. Copy this file into Winamps "plugin" directory. If you don't know how to do that, read the manual.

• AudioIO.h : The most important file for fellow C-programmers who want to use Audio-I/O in their own programs. It contains a simple interface to all audio-I/O-DLLs.

• *.c ,  *.h , *.dev , *.bpr : sourcecodes, headerfiles, and project files for DevCpp (which is a simple and free IDE for MinGW / GNU-C, if that means anything to you. If not, you can safely delete these files because they are not required to *use* the Audio-I/O-DLLs .

• readme*.txt : Some in-depth info for other programmers.

How to get started with the Audio-I/O-DLLs is described in the manual (PDF document). If you want to take a quick look without downloading and unpacking it, look here: AudioIO_Manual.pdf (beware, the manual in the archive will almost certainly be more update than the document on this website).

Sending an audio stream to an Icecast server with Spectrum Lab, Audio-I/O, Winamp, and Oddcast

This chapter is, at the moment, not much more than a hasty wish-wash of Spectrum Lab's author to send an audio stream to an Icecast server (thanks Paul for setting it up !)

You'll need a couple of programs to send your own stream...

• Winamp : Here, it reads the audio stream through a special Audio-I/O-DLL (in_AudioIO.dll), and sends the stream to Oddcast.

• Oddcast : Uses the Lame encoder to convert the audio stream into an MP3-compressed stream, and send this (compressed) stream through the internet (or, maybe, the local LAN) to an Icecast server.
  (In analog radio terms, Oddcast is just a "feeder", but not the "web radio transmitter", because your local ADSL connection will be too slow to feed more than one or two listeners at the same time)

• Icecast : Usually runs on a dedicated server hardware with broadband access. Details on www.icecast.org .
  Only if you want to stream into your local network, it makes sense to install an Icecast server on your local PC (for example, to listen to a remote radio receiver connected through a WLAN, etc).

In the configuration described below, Spectrum Lab receives the stream from a soundcard (or a software-defined radio), removes unwanted signals, and sends the output to Winamp. Let's start with this part:

Configuration of Spectrum Lab

Select the Audio-I/O-DLL as input source: In SL's main menu, select "Options".."Audio Settings and I/O device selection". Under "Audio Output Device", select "Audio-I/O DLL". Also set the output sampling rate to 22050, 32000, or 44100 samples per second (depending on the bandwidth. For a VLF "Natural Radio" stream, 32000 samples/sec is sufficient. For an SSB radio receiver, 11025 samples/sec is ok).

Configuration of Winamp

Make sure the file in_AudioIO.dll is in Winamp's plugin directory (details in the Audio-I/O manual).
To let Winamp use the AudioIO-lib for input (instead of reading samples from the soundcard, or from a disk file), select "Play"..."Open URL" (alias "Open Location" in older versions). In the input box, enter the pseudo-URL
audi://
and click "Open".

Start Spectrum Lab's processing (Start...Sound Thread), so it begins to fill the buffer in Winamp's input plugin. Shortly after that, Winamp should start playing the audio (which it receives from SL) to the speakers. If it doesn't, click the "play"-button. If that doesn't help, click the "stop" button, and again the "play" button. After this, Winamp should show the sampling rate and the number of channels (mono/stereo) which it receives from the Audio I/O library .

If you try to start Winamp's playback without SpecLab running, Winamp track timer gets stuck at zero, until it receives the first audio samples from Audio-I/O.

If this works, proceed...

Installation and operation of Oddcast

Download the Oddcast plugin for Winamp from www.oddsock.org . Install it as described (there are dozens of sites on this.. search for "internet radio station winamp oddcast icecast Lame" or similar..). BTW the Lame MP3 encoder library ( lame_enc.dll ) is sometimes in Winamp's plugin directory, but Oddcast expected it in Winamp's main directory (where winamp.exe is, too).

After installation of Oddcast, restart Winamp, and select "Options"..."Preferences"..."Plug-ins"..."DSP/Effect". In the list of DSP/Effect plug-ins, select "oddcast DSP vX", and click "Configure.." if the Oddcast panel doesn't open automatically. Add a new encoder, then select that encoder, and click on it with the right mouse button. In the context menu, select "Configure". There are three tabs, most important are the "Basic Settings". These must be carefully filled out.. for example:

Bitrate: 32 (which means 32 kBit per second compressed audio)

Samplerate: 44100 or 32000 (the latter preferred for VLF)

Channels: 1 (unless you send a quadrature stream from an SDR...)

Encoder Type: MP3 Lame (or OggVorbis, if supported by the receiving server)

Server IP, Server Port: Cannot tell you that...

Encoder Password : Won't tell you that...

Mount Point: If it doesn't work, try a forward slash before the stream name ;-)

Reconnect Seconds:  10  ( = default value )

On Oddcast's "YP Settings", give the stream a descriptive name and description.

Then close Oddcast's configuration panel ("OK"), and click "Connect" to try if Oddcast can connect the remote (or local, see below) Icecast server. If it doesn't work, get in touch with someone who knows a bit more about internet radio streaming than the author of these lines.

Installation and operation of Icecast

Icecast is, in analogy of the good old steam radio, the "radio transmitter" which is capable of broadcasting to dozen or hundreds of receivers simultaneously (your local ISDN- or ADSL uplink will not be able to do that).
Also, to check the SpecLab ->Audio-I/O -> Winamp -> Oddcast chain locally (without internet access), it makes sense to install Icecast besides Oddcast. Oddcast will then send the stream to Icecast, running on the same PC. Icecast contains an HTTP server which allows all users in your local network to listen to the audio broadcaster.
Installing and operating Icecast (within the local network) was surprisingly simple, using the default settings. To let Oddcast send the "feeding" stream to Icecast, set the "Server IP" in Oddcast to "localhost", and use port number 8000 (which is the default in the Icecast configuration).

< To Be Continued >

Good luck !

Wolfgang ("Wolf") DL4YHF .