SYNCHRO-SETTE VOL. 1 # 4 JULY 1982 CASSETTE LOADING PROBLEMS.
THE CASSETTE RECORDER.
As you know, many types of cassette recorders are on the market. The better ones can give a better sound quality to the computer. Some have valuable features such as a tape counter so that the user can identify the location of a particular program on the tape and/or a bass/treble adjustment that allows the user to raise the amount of high pitched sounds while the amount of low pitched sounds are automatically being lowered by the control at the same time.
The computer program pulses were produced by the computer as a high pitched sound and must be received back at the same pitch if the program is to load properly.
If the recorder only allows a mid range sound, then the high pitchs are of a lower intensity and any low pitched sounds that may be on the tape can over ride the high pitched pulses with interference and cause irregular transfer of data.
However, a recorder with a bass/treble adjustment must be set to allow maximum treble with no bass.
Even with these precautions, problems still can arise. If a program won’t load from tape, try removing the cord that goes from the MIC jack of the recorder to the MIC jack of the computer leaving only the cord to the EAR jacks. This prevents many of the unwanted signals from bleeding into the computer and causing audio distortion of the program pulses.
When saving programs on tape, do the reverse. Leave the MIC plugs plugged in and the EAR plugs disconnected. I personally test each tape before it is shipped to see that the programs load. One of the tests is to listen to the program’s audio pulses through a headset with ceramic earphones for noise distortion. One time while listening to a master tape that I had prepared, I noticed a background noise that wasn’t supposed to be there. I checked all my equipment and finally dicovered that my headphones were still plugged into the circuit between the computer and the recorder. I unplugged the headset and made another master tape. The background noise was now gone.
What had probably happened was this:
Earphones can operate as microphones in certain situations, picking up sounds from the surrounding envirnment. In many electronic project books it is shown how to use this effect to create an intercom device that uses a speaker that can act as both a microphone and a speaker. My headset had picked up background noise and sent it to the master tape. The recorder has a speaker for audio output when not used with the EAR jack. It is possible that background noise in the room may be picked up by this microphone and distorting your programs while you are trying to save them. Why leave them in when it is easy to disconnect this cord completely.
Try this test yourself by simply turning your TV volume up and listen to the sound as you slowly pull the plugs from the EAR and MIC jacks of the recorder. You can easily hear that the recorder itself is outputting a signal that shows up as the audio output of the TV changes.
Make your own test tape with at least two programs on the side you are testing and listen to it the same way. You will hear a lot more static and distortion before and between the programs than on the ones we sent you. Always, of course, make sure that you have run the tape beyond the leader that is on most cassette tapes before you start recording and turn the recorder on in its recording mode before you press the enter key on the computer.
If you still are dubious as to whether the slight amount of static is causing the loading problem, advance the tape beyond that segment and try loading again.
VOLUME CONTROL
This is one of the more critical areas of getting a proper load of a program. I have discovered a method of determining what I consider to be the exact volume setting for any one given program. Unfortunately for 1K machine owners, this method only works on 16K machines.
Sinclair suggests that your volume control should be set at 80% maximum volume and this is a good rule of thumb for the most part. Some tapes have the ability to produce a much stronger audio output signal at that setting than other tapes.
This results in a screen blitz where the computer hangs up and has to be reset. On the other hand, some tapes produce a lower audio output that results in the screen going white and the cursor returning to the bottom of the screen.
Try this following method on a program tape:
A. Type in LOAD”XXX” but don’t enter it yet.
B. Now select one of our 16K program tapes, put it into the recorder but don’t start the recorder.
C. Turn the volume of the TV up so that you will be able to hear the audio pulses.
D. Press play on the recorder and Press ENTER on the computer.
E. Find the portion of the program that has the even sounding pulses. It is usually the last part of the program. There are 24 pulses and this segment lasts 17 seconds.
F. If you have a tape counter, note the location where these pulses begin and where they end. If you don’t have a tape counter, time the seconds from the beginning of the tape to the first pulse. You are going to have to return to this segment a few times with the recorders fast forward and reverse keys (do not worry about the computer blitzing while you are stopping, starting and reversing the recorder. The computer is searching in vain for program “XXX” and will not bomb).
G. When you are comfortable with finding the location fo the pulses, at the point where the pulses begin, there should be 5 horizontal bars that are very steady. This situation will only last 17 seconds. Before these pulses, the bars do a lot of moving around so you are now going to adjust the volume so that these bars have very straight and clean edges.
H. Start turning the volume up until the bars start getting fuzzy edges (if you turn the volume too high, the bars may get wider and wider). When this happens, stop and turn the volume down slightly until the edges become crisp and straight again.
I. Make a notation on the cassette case itself of the volume level for future reference.
J. At this point, the volume is set as good as it can be. Hit the BREAK key. rewind the program and reload it in the normal fashion. The program should now load OK.
LOW QUALITY TAPES.
Many of us (myself included) have purchased cassette tapes at bargain prices and have used them on our computers with virtually no problems.
These non computer tapes are designed for sound input where high pitch or fidelity may not be important, such as for vocal or some music applications. The attempt to have the tape capture the high frequency sounds may not be successful and the replaying of the tape will easily evidence this effect, especially when we listen to the sounds directly and compare the same output on a quality tape.
This does not mean that you can not use them. Sometimes however, the tape has the effect of capturing the sounds in an irregular fashion. If we were to listen to the output of this type of tape we may hear some of the following undesirable effects:
A. Pulses that correspond with the position of the reel of tape as if a magnetic knife had cut through the reel.
B. Drop outs. The sound may be uniform in intensity and all of a sudden, the volume drops noticeably resulting in program blitzes. This can be the result of a lack of magnetic particles in that section of the tape caused by inferior manufacturing methods.
C. Uneven dispersion of magnetic particles in the tape causing drop-outs, uneven pulses, distortion, etc.
D. Left over sound pulses from old recordings that were not overlayed by the new program recording.
Many problems can be overcome with a bulk magnetic tape eraser but some are so stubborn as to defy the most rigorous attempts.
COMPUTER MALFUNCTION.
This problem is more common with those of us who built our computers from a kit. I have however, heard of some of our subscribers that have received defective computers from the manufacturer.
If your computer was built from a kit and is not loading or saving programs properly, check all of the connections for weak solder joints. If the solder joints are good, there might be a defective kit component. If you suspect a defective kit component or if your ready-built machine does not load the programs and you suspect the machine itself, it probably is best to have an experienced electronics service check it out or send it back to Sinclair for service.