Workshop Week 9

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A note about file links in this workshop:

As you work through this scenario, you should follow the steps as written. That is, if you read "I saved this file as XYZ.wav" you should save the file as XYZ.wav.

In many cases, by way of illustration, audio files representing intermediate steps in the design scenario will be available as an MP3 file for you to listen to. This is because MP3 files are easier to provide through the WWW. If you are working through the material you should not save your intermediate steps as MP3s, but keep working with wav files, only applying compression of necessary.

indicates a link to a file that has been provided by way of illustration. Clicking on will launch the sound in your computer's default media player. Should you wish to save the file to your hard drive right-click and select "save target as" (IE) or "save link as" (Netscape).

indicates a link to a file you will need to access to work through the example. You should right-click the link and select "save target as" (IE) or "save link as" (Netscape) to save these files to your hard drive.

 

WORKSHOP WEEK 9 MMST 12016

COMPRESSED AUDIO AND AUDIO FOR STREAMING

INTRODUCTION

Throughout this course we have been working with MP3 files, and in Tutorial 3 we looked at the concepts behind audio file compression and considered some of the issues surrounding the way MP3 files are "shared". There is one other important use of file compression that we have not yet covered: streaming audio.We are all familiar with the way in which the WWW and services such as Napster can allow for the transmission of files. In the case of the many MP3 files used on these pages, the principle is simple. The file is placed on a server, the person viewing these web pages chooses to download a file, and the file is sent via the HTTP protocol to the end user's computer. This model of transport is similar in many ways to the postal service: the file is a package sent from source to destination.There is another mode of transmission for compressed digital audio; streaming. Streaming is more like radio than post. An original audio file sits on a server. When someone wants to listen to the audio file, audio information derived from the file is sent, and recieved by a software application on the users computer, which converts the information into audio output. The file itself is not sent, just as the CD played in a radio station is not recieved by the listener.The principals of streaming audio are easy to understand. Remeber that the amount of information in compressed files such as MP3s is usually measured in kb per second. Internet conections are measured in kb (or Mb) per second. A typical modem is capable of connecting to the internet at 55.6 kb per second, and in practice may connect at around 30 to 40 kb per second. Assuming that there are no bottlenecks smaller than this on the path between the user and the streaming file server, someone with a 40 kb per second connection to the net should be able to listen to an audio file with a bit rate of less than 40 kb per second in real time. One obvious advantage for those wanting to make their audio content available for listenting, but not for direct saving and redistribution is that the file itself is not sent to the end user's computer. For example, if you right-click and save a link to a streamed RealAudio file, you will save a small file with information telling your RealOne player how to cnnect to the server, not the audio file itself.When one connects to a streaming media server using a streaming media player such as those provided by Microsoft (Windows Media Player) or RealNetworks (RealOne player) the following steps occur:1. The server begins converting the requested file to a stream of information analogous to a readio broadcast.2. The server begins sending the information3. The player starts storing information, so there is a buffer. If, for example, the player stores ten seconds of audio, and Internet congestion breaks the connection for eight seconds, the continuous stream heard by the user will not be interrupted.
Similarly, a user with a 40kb/s connection to the server will be able to listen to an three minute audio file with a 60 kb/s bit rate if the player waits to recieve a buffer of one minute of audio before it begins playing. 4. When the audio stream has finished playing, the connection is dropped.Some servers are quite intelligent, and can convert the bitrate (and hence the quality) of the audio stream on the fly to accomodate the quality of the connection between end user and server.There is nothing special about the file produced for streaming. MP3s can be streamed as well as more proprietary formats such as Real and QuickTime. What is particular to this mode of transmission is what happens at the server end, and the nature of the connection between the player and the server. This leads us to an important point: Be careful when deciding to use streaming media. No matter how good the software or hardware you use to produce compressed audio files for streaming, the quality and utility of the file for the end user will be determined by the following:
  • The quality of the connection between the server and the Internet
  • The number of concurrent hits on the server (i.e. concurrent requests for files)
  • The quality of the end user's Internet connection
  • The quality of the connection between the end user's Internet Service Provider and the Internet
  • Other variables such as internet traffic.

Terra Lycos' Webmonkey site contains much useful information, including this streaming audio tutorial, which you should read to gain a better understanding of this process.

As a producers of digital audio, it is important for you to understand the principles behind streaming, and know how to produce files that will be appropriate to serve up for this type of transmission. In this week's tutorial I am going to step you through the very simple process of preparing compressed .wma files for streaming. Note that the .wma file format is not different in quality to the MP3 files we have been using all term. WMA has been chosen as the encoder is freely available from Microsoft's WindowsMedia site and is very easy to use. If you want to know more about the range of compressed media formats available, it is worth looking at APC Magazine's article "the audiophiles".

THE EXERCISE

First, right-click on the link below to download a public domain aduio file of an Irish folk tune, Drowsy Maggie, played on that traditional Irish instrument, Yamaha ACXG synth chip.

maggie.mp3

Note that as this is already a compressed file, asn as such does not represent the full audio quality of the original. If you have access to the MMST12016 resource CD you will find a wav version in the "audio" folder.

You should open this in your audio editor, and save it as a wav file entitled maggie.wav, then follow the steps below.

Open Windows Media Encoder, and select "broadcast, capture or convert a file..." as shown below:

Note

With respect to Windows Media Encoder it is on the lab computers under programs/windows media. It is also on the term 3 cd under mmst12016\additional software\wm\WMENCODER71.EXE. It can also be downloaded at.

Windows Media Encoder

For Flex Students

The maggie.wav file is over 12 Meg you can down load it if you wish. However if you can source a wav file that you have on hand it will save you the down loading time.

Maggie track

 

Martin Francis

press "OK". Then, choose to convert an audio file as shown below.

"

Click "next". Press "browse" and navigate your way to maggie.wav. Then type a name for the wma file that the encoder will create.

You then have a choice of profiles. Each profile is a collection of settings appropriate for a particular scenario. Click the down arrow under "What profile do you want to use" to see the options...

... as you can see, there are quite a few. Let's select "Audio for CD-Quality"

You can then enter information that identified the track and carries copyright information. Were this file actually streamed, this information would be read and displayed by the Windows Media player on the end user's computer.

Click "next" and watch as the encoder processes the file. At this time the settings you have selected will be displayed.

Information about the session and the wma file will be displayed at the end of the process.

 

Now listen to the file, and compare it to the original.

maggie.wma

I followed the same procedure to produce two more versions of "maggie".:

This lesser quality setting produced maggie2.

An even lower bandwidth setting:

produced maggie3.

 

Exercises:

Download the following files:

mars.mp3

blumenstruck.mp3

and our old friend billdollar

Convert the first two to .wav format using your audio editor. Now attempt the following ecericses:

1. you are an aspiring electronic musician, and have just recorded your version of Holst's "Mars" from the Planets suite.

You want to distribute this as a bonus .wma file on your new CD. You also want to offer a 30 second streaming preview sample on your web site.

Produce two appropriate WMA files.

2. Your company as installed a new computer-based telephone system, and you have been asked to source some innocuous music to play to callers when they are placed on hold. Using Windows Media Encoder, produce a file from "blumenstruck" that will be as small as possible without losing any quality as heard over the telephone.

 

Extension Exercise

If you have time to spare it might be a good idea to use it to catch up an any exercises from earlier tutorials that you may not have completed. If you are up to date, you might want to carry out this exercise, for fun.

Download the fllowing files:

schumannblumenstuck.mid

mars.mid

maggie.mid

Open the files in AnvilStudio. Change the istruments for the various traks. You may be able to achieve some nteresting results. Here are some versions of blumenstuck with exotic instrumentation, courtesy of Anvil Studio:

dulcimer

sitar

steel drums

woodblock