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

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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


Static Audio Files

  • 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)

    • 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:

    • RealNetwork’s RealAudio

    • Windows Media Player

    • MPEG Layer III - MP3

    • Apple’s QuickTime


Perceptual Audio Coding

  • 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:

    • 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.


MPR’s 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.


Digital Audio Workstation

Protools Example


DAW and Sound files:

  • Sound file formats:

    • .WAV (Apple & Windows)

    • .AIFF (Apple)

    • .SND (Apple)

    • Sound Designer II (Apple)


Sound Files

  • 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:

    • Audiovault

    • Enco - Dad Pro32

    • DCart


Preparing Audio for the Web

Step 2 - Prepare Soundfile for Encoding


Audio Processing & Dynamics

  • 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:


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

Original Source

  • Audio Sample - 44.1 kHz 16bit Mono


Waveform View

Processed Soundfile

  • Audio Sample - 44.1 kHz 16bit Mono


Before and after processing

Original Source

Processed File


Preparing Audio for the Web

Step 3 - Real Audio Encoding


O=ginal urce

  • Audio Sample - 44.1 kHz 16bitMono


Real Audio Encoded


Coding Effects Comparison

  • Original Source File

  • Wave Convert Processed file

  • Real Audio Encoded


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.


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


Audio source flow

Compressor/Limiter

Source

Encoder


Audio source flow

Encoder

RealServer

End User


What if there are problems?

  • 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:

    • 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:

    • Controls SAS Router

    • Records appropriate source to a PCM Linear .WAV file.


MPR’s 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


MPR’s 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


Overall Goals

  • Reduce Bit Rate:

    • Keeps data costs down.

    • Reaches more people simultaneously.

    • Allows access to people on a dial up modem.


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/production/htmfiles/whatsnew.htm


Online Resources

  • Helpful articles to read:

    • http://www.sospubs.co.uk/sos/may00/articles/mp3.html

    • http://www.iis.fhg.de/amm/index.html

    • http://www.minidisc.org/PerceptualCoding.html

    • http://www.wired.com/wired/archive/7.08/codecs.html

    • http://www.webdeveloper.com/multimedia/multimedia_guide_realaudio_2.html


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