Positive and Negative uses of Real Audio for recording College Lectures


Prof. James Baird
Brown University
Providence, RI

Take a Look at a use of Real Audio and Adobe Acrobat-see Chem 22

Positives

  1. Very good compression. A 75 minute lecture compressed to about 5Meg.
  2. Lectures may be reviewed at a later time and at a location of the listeners choosing.
  3. Missed lectures may be heard.
  4. The Real Audio sound may be paused and if wanted material may be transcribed.
  5. It is not necessary to down load an extensive sound file.
  6. Sections of a lecture may be selected for listening.
  7. A view of the player:

  8. I am very enthusiastic and satisfied with my use of RealAudio this year.

Currently, I have encoded over 2,300MB of audio which occupies about 97.1MB on the Chem 277 quantum chemistry course server and over 2,000MB of audio occuping about 88.9MB of Chem 22 first year chemistry lecturers. Ideally, RealAudio emanates from a server so that the recipient does not have to download a large file, only about 11KB of a URL. The jcbmac.chem.brown.edu server uses a RealAudio server for lecture material in Chemistry 22. Students may, if they wish, download the URL and listen to portions of a lecture at their own convenience. Every lecture has been encoded.

Negatives

  1. Time Costs:
    1. The lecturer must record and organize the recording into appropriate segments.
    2. A TA must enter the recording into the computer and encode (compress) the files.
    3. The encoded sound must be added to the course web page.
  2. Need adequate audio equipment. Should be unobtrusive. I am using an inexpensive Radio Shack cassette tape recorder. The sound quality is not so good.
  3. Need to manipulate the sound file using a program like SoundEffects-remove extraneous sounds and dead spaces. Using a Power Mac 7100/80 with the limitations of Sound Effects 0.9.2 this can be time consuming.
  4. Need to have a server in order to have "streaming" audio. Otherwise the sound file must be downloaded.
  5. Sound files occupy a lot of disk space. A semesters worth of lectures may be about 100 Meg of RealAudio.
  6. Students and others must have appropriate computer equipment for sound.
  7. There is a time cost to students to listen to sound files. The idea of breaking the lectures into smaller segments is to facillitate the listening problem. Of course the genius of Real Audio is that down loading of the sound file is not necessary.
  8. Such a system may promote lecture absenteeism.
  9. Illustrations have to be added - that is, overheads need to be correlated with the lecture segments.
  10. Propagation of errors: A lecture is ephemeral up to this point and errors are lost to the winds. With Real Audio such things persist until the audio file is erased.
  11. The lecture is publically accessible. This only presents a problem, and there are internet ways around it, when a cost has been paid by the student for access to these lectures.

Answers to the Negatives

  1. There is no answer to the cost in time. If this technique is found to be worth while then the time cost will be borne. Using a Power Mac 7100/80 each minute of audio requires one minute of Real Audio encoding. A fast work station is usefull.
  2. For a lecture a sound file may be 73 MBytes. Loading such a file takes time and filtering it, etc., is also time consuming. Best to have good quality sound recorded at the beginning so that manipulation is not so necessary. Also, the lecture should be broken into segments-besides the Real Audio ram file segments-to make the audio file more amenable to loading into computers if that is required.
  3. In RealAudio there is a Play List that lists the paths to the audio ram files. It would be convenient if this list could be the titles of the audio files since manipulation of the order of the audio could take place at this point rather than going back and forth between audio files and the html page.
  4. I have been editing the sound files prior to encoding with RealAudio using Alberto Ricci's Sound Effects 0.9.2 removing silences, normalizing and smoothing. Have not removed background noise. In anycase, this is the wrong strategy caused by using an inexpensive tape recorder rather than a good sound system. Because of the poor quality I have been keeping the 22KHz frequency feeding to RealAudio. Due to the current limitations of Ricci's application I can only handle 10 minutes of sound at a time.
  5. Perhaps a better technology is to broadcast directly into the computer digitizing on the fly. Digitizing at 11.1KHz is reasonalble in audio quality for the spoken word and cuts the file size in half relative to 22KHz. (11/2/95 - think it better to use a high quality tape recorder with some input filtering.)
  6. The next experiment is to record into a good quality Maranzt recorder having some low pass and high pass filtering on the input and then digitizing. Lectures are inherently spontaneous and therefore there are pauses and other glitches that do not occur from scripted material. This means that some signal processing is needed. A script defeats the purpose of this experiment.
  7. A Marantz portable cassette recorder PMD222 was used 10/23/95 to record an hour lecture a portion of which is here. Needless to say the quality is superior to my Radio Shack CTR-96 Model 14-1105 recorder. After recording directly into the mic on the recorder I digitized at 22KHz using a recorder taken from the internet. In one case I edited the recording using Ricci's Sound Effects. On the rest I just encoded into RealAudio. A Calrod 10-4 Electret tie clip mike was also tested. Needless to say, a mike near the sound source (clipped to my shirt) has far less background noise than does a mike sitting on a table and using much of its automatic volume control to pick up a lecturer's wandering voice (that is to say, the signal to noise is vastly improved). The electret mike is quite satisfactory!
  8. Here are two recordings using the Radio Shack recorder on voice activation and digitized using Sound Machine at a sample rate of 22.1KHz, 8 bit mono. This was encoded first with RealAudio 1.0 and then using RealAudio 2.0b1 at 14.4K. The encoding with RealAudio 2.0b1 takes a bit longer. 67.6 sec of sound took 103 sec to encode using RA 2.0b1. 1.4MB sound file encoded to 66.2KB at 14.4KHz. The quality of the sound seems better. The use of the Script allowing multiple encodings is a very good thing! One problem with voice activation is an occasional missing sound and a sharp sound.
  9. I purchased a Marantz PMD222 recorder and a Shure SM11 dynamic lavalier microphone with response from 50Hz to 15,000Hz. With CrO2 tape the Marantz frequency response is 40Hz to 14KHZ so that these two are well matched. Wearing the mike with a tie tack gives quite acceptable sound. Encoding with the RealAudio 2.0 encoder at 14.4KHz takes a while, but I think the result is fine. Students have accessed the lectures in RealAudio in order to review material, or even listen to it for the first time!
  10. Equipment problems. This is a real one. Not every student can afford a computer. More and more have them and universities have clusters. Sound is not practical in a large room with clusters of computers unless ear phones are available. The ear phones do not have to be expensive however and this may be a good solution. At Brown University the computer clusters are widely used. Most dorm rooms are connected to ethernet and some to modems (to be replaced). Students report that it is very convenient, even using the modems, to have all the course material in their rooms. One downloaded RealAudio player and the Adobe Acrobat reader over a modem running at 9600 bits per sec. He did this early in the morning for obvious reasons.
  11. Down loading RA files over modems at 14.4Kb/s is time consuming, but streaming as designed by RealAudio is satisfactory. An ethernet connection is the only practical method for down loading 500KB files. Many dorm rooms have ethernet connections and computer clusters provided by the University are so connected. The answer to this is also to have a Real Audio server so that the entire audio file does not need to be down loaded.
  12. The RealAudio server 1.0 for the Mac has been installed. It does not support 28.8KHz sound files so they must be downloaded to be played using the 2.0 player. The server folder needs to be in the same directory as MacHTTP, or Webstar. The PC 2.0 server is available and the Mac version is due soon so that 28.8KHz sound can be served from MacIntosh.
  13. As to lecture absenteeism this is already an effect. There is an advantage to attending lecture. Besides the personal touch, there is the possibility of asking questions and getting answers and the give and take of the classroom. Also, lecture demos, while capable of being videoed and digitized (see the oscillating reaction in the Special Topic Cicadian Rhythms in Chem 22) are very computer space demanding and also time consuming in terms of preparation. There are commercial video disks that take care of this problem. Eventually, there may be many video disk players around the campus.
  14. The introduction of "ConcepTests" advocated by Eric Mazur where students engage in peer instruction in class requires attendance. To see where I am going with Internet Active Concept Tests. Click here for Test 1 and Here for Test 2
  15. As to errors, they always exist and we constantly correct for them. These audio recordings probably should be removed at the end of a semester. Besides, a semester worth of lectures is about 125 Megabytes compressed! Even though gigabyte storage is not very expensive (just paid $360 for 1 Gig) it does not seem, at this point, lectures should be saved from year to year. In my case, no lectures are the same.
  16. Illustrations can be added as picture files made from the overheads that are used. The overheads originate in a computer and making a gif picture file is just another time cost, but one made easy by Yves Piquet's clip2gif.
  17. The use of RealAudio 2.0 ability to stream images (synchronized multimedia) such as overheads and better to use a URL to pages in an Adobe Acrobat book such a my lecture notes is a real advantage!
  18. Public accessibity has been the purpose of the internet. However, commercial ventures are changeing that and the case of lectures at universities are not immune to these problems. That is, why if a student pays a tuition to hear lectures should these be made free over the internet?
  19. Finally, Audio Hints from RealAudio.

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