Now that we have our sound card working, it's time to check out some of the options that we have for playing sound. If you're following the course in order of the lessons, we haven't begun to talk in depth about the use of the X-window system in Linux, so the tools for playing and recording sound here will be used from the command line.
I'd also like to add an editorial comment, if I may. I use a window manager but the programs I listen to CDs, MP3s etc. are command line applications. I am not implying that there aren't some fine programs for playing and recording sound. There certainly is some nice stuff out there. The programs I use (which we'll talk about here) are great applications that work just as well as their graphic counterparts but in many ways are more easily configurable, at least for me. Besides, we're talking about sound, so I just have to set the CD or playlist and listen. I really don't have to see anything.
Recording Sound
Due to Microsoft's monopoly on operating systems (yes, they have been convicted of this in a court of law), the most popular format for sound recording is is their *.wav format. When you make a recording of yourself or someone else speaking or you "rip" a track from a CD for later conversion to mp3 or ogg (we'll talk about this new and open format later), you're probably going to use the *.wav format. If you simply want to record yourself saying something using Linux, all you need is a microphone and and recording tool that gives you a file in this format. For this lesson, we'll use 'wavrec'.
'wavrec' is easy to use. It's easy because the default recording settings for this applications are all acceptable for getting a quality recording (if you've got a fairly good microphone). You just have to type some simple commands and you're all set.
Here's an example:
Let's say I want to record a note to myself that says the following: "Note to self: make sure you respond to Dave's email about SuSE'. I would just type the following"
wavrec dave_note.wav
make sure the microphone is on (you'd be surprised how many times I forget to turn it on!) and start talking. The default recording time for 'wavrec' is 10 seconds. That means, if you don't specify a recording time on the command line (I didn't) you'll get a 10 second long sound file. My sentence above, "Note to self ..... bla bla bla" lasts about 8 seconds. Of course, the duration of the sound file depends on whether you're talking a normal rate. If you auction cattle in Iowa, then you probably don't need 10 seconds to say that sentence, so you should modify the time for the file, like this:
wavrec -t 3 dave_note.wav
The -t option refers to seconds, so you should type the number of seconds after. Here, even 3 seconds might be pushing it for a cattle auctioneer. Just remember to give yourself enough time for what you want to say, in seconds. If you want to recite Abraham Lincoln's Gettysburg Address, then you would first multiply 60 and 2 to get 120 seconds. Why this figure? Because Lincoln is reported to have taken only 2 minutes to give this famous speech. If you would like to record Cuban leader Fidel Castro's speeches, then I would advise getting a huge hard drive. He once made a speech that lasted 7 hours.
You can add all kinds of options to wavrec. I use this tool all the time to record short sentences for use in computer assisted language learning. Here are the values I use:
wavrec -S -t 5 -s 44100 a_sentence.wav
Let's explain these options. The first one, -S, means stereo. If you look at the man page for 'wavrec' (type: man wavrec), it says that stereo is the default. Nevertheless, I have noticed that mono is in fact the default. That is to say, if you use 'wavrec' with no options, you get mono not stereo sound. It would seem there is an error in the man page. After the -S, we have the -t option for seconds (we explained before) then we have the -s option which is the sampling rate in Hz. I chose 44100 because this is a good high-quality sound which is necessary for my language teaching endeavors. It's important not to confuse the -S (capital letter) with the -s (lower case). -s takes a value in Hz while -S has no value. I have purposely put the -t option in between them to avoid confusion. There you have it. Issuing this short command and then changing the file name, I get a lot of work done because my sentences seldom last more than 5 seconds and these values are fine for my work.
Now, you must be asking the question: "I've made a *.wav file, now, how do I hear it?" The answer is easy: With 'wavrec' 's companion program, 'wavplay'. Here's how:
wavplay a_sentence.wav
This will play the sentence we recorded above. That's all there is to it. I should also point out that the same options in 'wavrec' are available for 'wavplay' if you want to add some effects to playback. For example, if you take our first wav file, dave_notes.wav, and play it like this:
wavplay -s 44100 dave_notes.wav
you'll find it's doubly fast. That's because our note about Dave was recorded at the default 22050 hz, so if you do the math, you see that what we've done is double it's sample rate . You might want to do this:
wavplay my_favorite_song.wav
then sing a line of your favorite song. Play it back to your friends using the -s 44100 option and have them rolling on the floor with your Alvin and the Chipmunks impressions. I have actually entertained my 2 year old son for hours with this.
Using the same logic, if you take our a_sentence.wav and play it like this:
wavplay -s 22050 a_sentence.wav
you've cut the sample rate in half and so you get a really cool impression of the creatures that take over people's bodies in Star Trek's original series episode 'The Lights of Zetar'.
I know what you're probably thinking. I need to be productive. I don't want to record Chipmunk sounds and sci-fi weirdness. Well, then. Here's a good way to use these tools, plus a couple of other command line tools to read reminders to yourself in the morning, or whenever you'd like. First, create a subdirectory in your own directory /home/[you]/
mkdir reminders
then go into reminders (type: cd reminders). Now, Let's create a sort of introductory wav file that's always going to be there. I'll explain why we need that in a bit.
wavrec -t 3 0intro.wav
Say something like "Your reminders" or "Reminders for you". Three seconds should be enough for that. You may have noticed that the name begins with zero. That is simple because for our reminder system, we invoke 'wavplay *' with the asterisk to play every file in that directory. By naming it '0intro.wav', that assures that it will be played first with our system.
Now record some reminders. I recommend using a YEAR-MONTH-DAY format plus some meaningful word for naming the wav files. For example, type:
wavrec -t 5 2001-10-24_trash.wav
and say: "Remember to take out the trash". I suppose 5 seconds should be enough to say this. Try recording a few more reminders for different things, like "call cousin Jack" and "remember to pay back gambling debts to bookie". When you've got a few wav files in there you should play them to see that they've come out all right (you don't need to do this every time - we're just practicing)
wavplay *
You'll see that the 0intro.wav file gets played first. If everything sounds good to you, then we're ready for the next step which is to play our files automatically at a given hour.
One of my favorite applications in Linux is called 'cron'. This is a pretty powerful tool that is used primarily by system administrators to automate their tasks and duties. It's powerful because it can schedule something to be run automatically at any time, whether that be once every three minutes, every hour, once a day or every Thursday. It can even be used to run a job that you do only in January. But just because it's powerful, it doesn't mean it's complicated to use. For our purposes, it's very simple to configure 'cron' to play our reminders. First, we have to edit a file that is called 'crontab' and add our instructions. There is a system-wide crontab file for root's exclusive use, but there is also one available to every user to run command line apps that he or she is authorized to use. To add a job to be done, just type:
crontab -e
Then we add the following line to our crontab file (-e is for edit)
30 7 * * * /usr/X11R6/bin/wavplay $HOME/reminders/*.wav
The crontab edit procedure uses your default command line editor which is probably 'vi', so if you don't remember our little tour of 'vi', just press 'ESC + i' before you add this line.
Let's explain how a crontab file works. The file is read by the program 'cron' and it carries out the instructions in it. In our example, our wav files get played at the 30th minute of the 7th hour, that is to say 7:30 in the morning. This is because the crontab file must start with the minute [0-59] you want something done, followed by the hour [0-23] the day of the month [1-31], the month of the year [1-12] and the day of the week [0-7] (where 0 and 7 are both Sunday). I have left the last three as asterisk. This tells 'cron' that these values don't matter. That is to say, cron should play our *.wav files every day of the month, every month of the year, 7 days a week.
The next step as you can see is to tell cron to run 'wavplay' and play the files in your home directory. We use the symbol $HOME for that. Also notice how I have put the exact path to where wavplay is. To see if your system differs, then type:
which wavplay
to show you where the program is. Then adjust accordingly. I used this exact path because, it would seem on my system, the master crontab file (found in /etc/crontab ) doesn't recognize that path automatically. I am assuming that this is for security reasons, so I didn't go in and change the path. Some things are probably best left alone, so no harm done if you just put in the exact path in the crontab file.
If you want to test it, just give it a time within a couple of minutes or so. That is, if it's 3:30 in the afternoon, you might want to first edit your crontab like this:
32 15 * * * /usr/X11R6/bin/wavplay $HOME/reminders/*.wav
that will play the reminders at 3:32 PM, to show you that it works. Just make sure you're not playing anything else, like MP3s, because you won't hear them. That's the rationale for my 7:30 AM start time. It's a good hour for me - when I am just getting to work and I'm probably not listening to heavy metal at that hour of the morning. Actually, I never listen to heavy metal.
Now, when you've finished hearing them, you can delete them (if you want) That's where the rationale behind the YEAR-MONTH-DAY.wav comes in. You just delete the daily ones by typing, for example rm 2001-09-28*
That keeps the 0intro.wav file in there. I mentioned before that I was going to explain why it's necessary to have it there. 'Cron' will mail you when there is an error, so if you had no reminders for a given day, you would at least have one file in the /reminders directory. That way, 'cron' doesn't have to mail you an error message because the program 'wavplay' didn't find any *.wav files.
By deleting the unnecessary reminders, you've got some free disk space. Speaking of that, if free disk space is something that worries you, in the next part of the lesson we'll talk about those famous (and controversial) files that take up less space - MP3s - and how to make them under Linux. We'll also talk about the new free audio format comparable in sound and space to MP3 - Ogg Vorbis.
