Preparing Audio for the Internet - Nick Kereakos - MPR Topics Covered: Topics Covered:  Static Audio Files  Audio Streams  Automation

Static Audio Files What is it? What is it?  Standard computer data file  Data reduced for internet broadcast  Audio encoded using a bit reduced perceptual audio coder.

What do I need? Digital Audio Workstation (DAW) Digital Audio Workstation (DAW)  Personal Computer with an audio card.  Digital Audio Workstation software. Ex.) Protools, Cubase, Sonic Solutions, Peak Audio, Sonic Foundry, Cool Edit, etc…

Digital Audio Workstation Protools Example

Perceptual Audio Coder Standard Coders include: Standard Coders include:  RealNetwork’s RealAudio  Windows Media Player  MPEG Layer III - MP3  Apple’s QuickTime

Perceptual Audio Coding Principles: Principles:  Aims to achieve fidelity perceivable by humans.  This means removing sound we cannot hear.  Reproducing sound we can hear.

Preparing Audio for the Web Step 1 - Convert Analog source to Digital

Method’s Use DAW: Use DAW:  Prepare & Edit Digital Audio File  Process the file  Encode file with Encoder of choice Use Only Encoder: Use Only Encoder:  Record audio source with Encoder  Create an encoded audio file.

MPR’s Method Use a DAW: Use a DAW:  Increased flexibility  Original Source file  Can be use for multiple Encoders  Ability to edit content  Better sound quality  Integration with Broadcasting & Automation systems.

Digital Audio Workstation Protools Example

DAW and Sound files: Sound file formats: Sound file formats: .WAV (Apple & Windows) .AIFF (Apple) .SND (Apple)  Sound Designer II (Apple)

Sound Files PCM Linear Audio File: PCM Linear Audio File:  CD Quality 44.1 kHz, 16bit  Broadcasting standard audio file  Non data reduced  Cross platform

Sound Files Broadcasting Systems using files: Broadcasting Systems using files:  Audiovault  Enco - Dad Pro32  DCart

Preparing Audio for the Web Step 2 - Prepare Soundfile for Encoding

Audio Processing & Dynamics Process the sound file: Process the sound file:  Compression - reduces dynamic range  Limiting - to set brick wall upper audio limit  EQ, to soften upper frequencies

Audio Processing & Dynamics MPR uses WaveConvert: MPR uses WaveConvert:

Audio Processing & Dynamics  Compression - Reduces dynamic range the Encoder needs to calculate. For lower bit rates, this is especially important and effective.  Limiting - This avoids distortion for the end user listening via the Web.  EQ - Softens inherent harshness of low bit rate encoded audio.

Digital Audio Levels Analog Meter Digital Meter

Digital Audio Levels Analog Meter Digital Meter

Waveform View Audio Sample kHz 16bit Mono Audio Sample kHz 16bit Mono Original Source

Waveform View Audio Sample kHz 16bit Mono Audio Sample kHz 16bit Mono Processed Soundfile

Before and after processing Original Source Processed File

Preparing Audio for the Web Step 3 - Real Audio Encoding

Audio Sample kHz 16bitMono Audio Sample kHz 16bitMono O=ginal urce

Real Audio Encoded

Coding Effects Comparison  Original Source File  Wave Convert Processed file  Real Audio Encoded

Web Audio Stream Uses same exact principles Uses same exact principles  Audio is sent as a continuous data stream rather than existing as a static file.  Data is reduced for internet broadcast  Audio encoded using a bit reduced perceptual audio coder.

Audio Processing & Dynamics Process the source: Process the source:  Compression - reduces dynamic range  Limiting - to set brick wall upper audio limit  EQ, to soften upper frequencies Use outboard audio equipment: Use outboard audio equipment:  Compressor/Limiter  EQ, to manipulate frequencies

Audio source flow Source Encoder

Audio source flow End User EncoderRealServer

What if there are problems? Monitor your stream: Monitor your stream:  Install a PC to playback the stream.  Wire the output of the PC’s audio card to a silence sensor.  When the alarm goes off, you know there is a problem with the stream.

Monitoring the Stream will alert you when:  The Encoder fails  The source is interrupted or fails  Your Network fails

Automated Static Web Encoding Process: Process:  Source Audio file is compiled/recorded  Dynamics are applied to the audio file  File is processed in Real Producer  Web Encoded file is delivered to destination

MPR’s Design ENCO - Dad Pro 32: ENCO - Dad Pro 32:  Controls SAS Router  Records appropriate source to a PCM Linear.WAV file.

MPR’s Design Static Encode Box: Static Encode Box:  Running Windows NT 4.0  NT script moves file from ENCO drive  WaveConvert Pro applies dynamics to.WAV file and creates new file  Real Producer encodes new.WAV file  Newly encoded file waits for delivery

MPR’s Design Caravan: Caravan:  Developed by MPR Online personnel  Script runs 24 days monitoring directory contents  When a new Real Audio file is delivered, Caravan moves it to its proper location

Overall Goals Reduce Bit Rate: Reduce Bit Rate:  Keeps data costs down.  Reaches more people simultaneously.  Allows access to people on a dial up modem.

Online Resources Real Networks: Real Networks:   Real Producer is free  Real Player is free  User forums and FAQS are helpful  mfiles/whatsnew.htm

Online Resources Helpful articles to read: Helpful articles to read:      _guide_realaudio_2.html