Digital Audio Recording (DAR)
With the advent of digital audio, many of us have long since disposed of our analog stereo recording equipment such as cassette and reel-to-reel recorders in favor of digital recording and digital playback. We've learned how to create MP3's from our CD's and transfer them to a portable MP3 player. Some MP3 players come with a built in FM receiver and even fewer ones come with an AM receiver. If you are close enough to an AM Station's transmitter, you should be able to get good reception and a fairly good recording but good AM reception requires a large internal ferrite antenna that is actually larger than all portable MP3 players. Recording great audio in mono or stereo can now be done by simply connecting the line-out from a radio or receiver with good reception to the Auxillary Audio Line Input of a computers sound card and using audio recording software. We can record music, a talk show program, or whatever and store it directly as a digital MP3 file onto your computers hard drive. From this point we can copy these audio files into a portable MP3 player or onto CD media if we so choose. For those of us who still own an analog recorder, we still have the ability to record up to say 45 minutes per side on a cassette or even more on a reel-to-reel deck. The problem I've run into is getting a solid recording of an AM Radio Talk Show that runs 4 hours in length onto my computers hard drive in a digital format. My computer is a Pentium 4 2.8GHz with 2gigs of RAM and plenty of hard drive space for days and days of recording time. The problem is, I'm constantly using my computer to run a wide variety of programs and most all of these programs will at times produce audio of some sort and if I were recording my favorite Talk Show, these additional sounds will be mixed in with my Talk Show audio making it a completely unacceptable recording. If I simply shut down these other programs and dedicate my computer to recording audio, it would be perfect, but then I wouldn't be able to use my computer for 4 hours until the Talk Show was over. Well, you're probably saying, "why don't you just use your cassette recorder?" I could record a 4 hour program onto say 4 60 minute cassette tapes then transfer that audio in real time into my computer, but I'm still looking at the same problems of having to dedicate the computer to this task for 4 hours. There are specially made cassette recorders that will record several hours and more of audio onto one side of a cassette tape but we are still face with the problem of transferring that audio onto our computers hard drive and converting it into a digital format. I've come up with a simple and inexpensive solution to this problem and am sharing it here.
The next time you're walking down the isles in the Electronic department of your favorite store, look for those new small portable digital audio recorders. Some of these are very inexpensive running in price of around $25 dollars and up. The one I purchased has one recording mode with a frequency response of 20Hz to 16Hz which is overkill for recording the frequency range of the human male and female voice and almost perfect for music which is much more demanding. The higher the recording frequency response of these small digital audio recorders, the higher their price is and more memory is required to record the same amount of time. The problem with most all of these digital recorders is they are not built with an audio-in jack, but most all have a External Microphone input jack. It is this jack that we can use to record audio from a radio receiver or other audio source. What I've done and what you can do for only a few dollars is to construct a simple audio patch cord. With this patch cord, we can connect the output of the receivers Headphone jack to the digital audio recorders microphone jack. There are two types of patch cords one can build. One is a mono type and the other is a stereo type. The following picture shows the basic construction of a mono patch cord. The stereo patch cord requires two stereo phone plugs, two 200K ohm 1/8 watt resistors and a three wire shielded cable. You can use a three wire shielded cable to build the Mono Patch Cord, it's just that you don't use the third wire.
Assembly:
The length of my patch cord is two feet. Make sure both plastic screw on caps for the phone plugs are placed onto the cable before you solder the wires on the final phone plug. Connect and solder the shield wire to the ground lug on both phone plugs where indicated. On the left phone plug, solder one lead of the resistor to the tip terminal of the phone plug and the other end of the resistor to one of the other available cable wires. On the right phone plug, solder the opposite end of the same wire connected to the resistor to its tip connector. When you complete the soldering, you can screw the plastic caps back onto the phone plugs to complete the assembly. The resistor is needed to reduce the amplitude of the Headphone Output so that we don't overdrive the Microphone input of the DAR producing distortion. You can buy the shielded cable, phone plugs and resistor(s) at Radio Shack or most any Electronics store. You may want to play with different values for your resistors depending on your choice of DAR. Different DAR's may have different Microphone input impedances. You can partially assemble the patch cable leaving the resistor out and then use small clip leads to connect in different values of resisters to find out what is best for your setup. Also, some DAR's may have several microphone sensitivity settings that you will want to consider. I've selected my value of resistance using the most sensitive microphone setting. If you need to build a patch cable for recording in stereo, use a three wire shielded cable with two stereo phone plugs and two resistors of equal value. Just add the second resistor to the right stereo phone plug using the third wire to connect back to the left stereo phone plug. If your stereo recording(s) happens to have the left and right channels reversed, just swap the two wires on either the right or the left phone plug leaving the shield wire where it is.
Recording Tips:
When your patch cord is complete, simply connect one end to the receivers Headphone output jack and the other end of the patch cord to the DAR's Microphone input jack. My DAR has a Headphone jack so I plug my headphones into the DAR and start the recording. The only adjustment is the volume control on the receiver. After starting the recording, you can monitor the quality of the recording through the headphones and determine the exact position of the volume control on the receiver. In my case, it doesn't take much volume to get a good recording and to much volume will cause audible distortion which you can hear through the headphones. My DAR has a built in VU Meter which gives me a very good indication for setting the proper recording level.
Once you're done recording, simply upload the audio file(s) from your DAR to your computer, maybe do some minor audio processing and your done! My portable DAR runs for 8 hours and more off of one AAA battery. I use AAA Nickel-Metal Hydride rechargeable batteries so I don't have to spend extra money keeping a large supply of Alkaline batteries around. I just recharge them when they run low and I'm ready to go for another 8 hours of recording. Nickel-Metal Hydrides will pay for themselves after 3 or 4 recharges and you're good for 1,000's of more recharging cycles.
I've seen only one MP3 player on the market that has a built in AM radio and customer feedback on it's reception of AM signals isn't good. So if you're not right next door to the AM stations transmitter and don't like the idea of spending $200 to $300 dollars on one of these units, consider building a simple patch cord if you already own a good AM reciever. All you need spend is around $30 to get great digital audio recordings that easily transfer onto your computers hard drive.
I hope this is of some help to you DAR buffs. Good luck and enjoy making high quality Digital Audio Recordings! ;)