Preparing Audio for the Internet Nick Kereakos MPR

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Preparing Audio for the Internet -Nick Kereakos -
MPR

• Topics Covered
• Static Audio Files
• Audio Streams
• Automation

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Static Audio Files

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

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What do I need?

• 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

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Digital Audio Workstation
Protools Example
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Perceptual Audio Coder

• Standard Coders include
• RealNetworks RealAudio
• Windows Media Player
• MPEG Layer III - MP3
• Apples QuickTime

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Perceptual Audio Coding

• Principles
• Aims to achieve fidelity perceivable by humans.
• This means removing sound we cannot hear.
• Reproducing sound we can hear.

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Preparing Audio for the Web

• Step 1 - Convert Analog source to Digital

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Methods

• Use DAW
• Prepare Edit Digital Audio File
• Process the file
• Encode file with Encoder of choice

• Use Only Encoder
• Record audio source with Encoder
• Create an encoded audio file.

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MPRs Method

• 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.

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Digital Audio Workstation
Protools Example
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DAW and Sound files

• Sound file formats
• .WAV (Apple Windows)
• .AIFF (Apple)
• .SND (Apple)
• Sound Designer II (Apple)

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Sound Files

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

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Sound Files

• Broadcasting Systems using files
• Audiovault
• Enco - Dad Pro32
• DCart

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Preparing Audio for the Web

• Step 2 - Prepare Soundfile for Encoding

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Audio Processing Dynamics

• Process the sound file
• Compression - reduces dynamic range
• Limiting - to set brick wall upper audio limit
• EQ, to soften upper frequencies

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Audio Processing Dynamics

• MPR uses WaveConvert

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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.

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Digital Audio Levels
Analog Meter
Digital Meter
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Digital Audio Levels
Analog Meter
Digital Meter
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Waveform View
Original Source

• Audio Sample - 44.1 kHz 16bit Mono

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Waveform View
Processed Soundfile

• Audio Sample - 44.1 kHz 16bit Mono

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Before and after processing
Original Source
Processed File
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Preparing Audio for the Web

• Step 3 - Real Audio Encoding

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Oginal urce

• Audio Sample - 44.1 kHz 16bitMono

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Real Audio Encoded
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Coding Effects Comparison

• Original Source File
• Wave Convert Processed file
• Real Audio Encoded

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Web Audio Stream

• 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.

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Audio Processing Dynamics

• Process the source
• Compression - reduces dynamic range
• Limiting - to set brick wall upper audio limit
• EQ, to soften upper frequencies

• Use outboard audio equipment
• Compressor/Limiter
• EQ, to manipulate frequencies

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Audio source flow
Compressor/Limiter
Source
Encoder
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Audio source flow
Encoder
RealServer
End User
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What if there are problems?

• Monitor your stream
• Install a PC to playback the stream.
• Wire the output of the PCs audio card to a
  silence sensor.
• When the alarm goes off, you know there is a
  problem with the stream.

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Monitoring the Stream will alert you when

• The Encoder fails
• The source is interrupted or fails
• Your Network fails

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Automated Static Web Encoding

• 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

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MPRs Design

• ENCO - Dad Pro 32
• Controls SAS Router
• Records appropriate source to a PCM Linear .WAV
  file.

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MPRs Design

• 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

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MPRs Design

• 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

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Overall Goals

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

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Online Resources

• Real Networks
• http//www.real.com
• Real Producer is free
• Real Player is free
• User forums and FAQS are helpful
• http//service.real.com/help/library/guides/produc
  tion/htmfiles/whatsnew.htm

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Online Resources

• Helpful articles to read
• http//www.sospubs.co.uk/sos/may00/articles/mp3.ht
  ml
• http//www.iis.fhg.de/amm/index.html
• http//www.minidisc.org/PerceptualCoding.html
• http//www.wired.com/wired/archive/7.08/codecs.htm
  l
• http//www.webdeveloper.com/multimedia/multimedia_
  guide_realaudio_2.html