cell phones and driving…it’s gets technical!

Just about every year, some politician brings up banning using cell phones in cars while driving.   The typical argument is what is the difference between using a cell phone, and using a 2-way dispatch radio like a CB or a police radio while in a car?  Are those devices just as distracting?  Also, what about pilots?  Don’t they use radios to communicate with the control tower?  Why aren’t distracted pilots crashing airplanes?

There are significant differences in the way other radio devices are used, and the way people use cellular telephones.  The biggest difference is in the length of conversations that take place on dispatch radios versus cellular telephones.  A police dispatch basically starts with “Unit 53, respond to 123 Elm street on a domestic”  And the officer may respond with a quick “10-4, Unit 53 responding”  The conversation does not go much farther than that.  This argument has come up several times,  but there are much larger factors involved as to why cellular telephones are more distracting.

As a licensed amateur radio operator, I can place cellular telephone technology against the test of common 2-way radio equipment to find the differences.  The most obvious difference is in the radio itself.  Most dispatch and other 2-way radios use a full-size speaker mounted to the radio itself that the user hears without an earpiece.  Some 2-way radios have VOX or voice activated transmiters, but most use a simple hand-held microphone with a push to talk switch.  These radios are half-duplex meaning that one party must stop talking before another starts.   This allows for a slower flow of conversation.

From a more technical side however lies the audio quality of a cell phone versus a two-way radio.  Most two-way radios used for public service (police, fire and rescue) operate using FM, which is the same technology that you listen to music with on your broadcast radio.  Other two-way radios use AM or even sideband technology which is similar to to what you may listen to talk radio on.  While AM technology is very old and has less fidelity than FM, it still is better quality than the digital CDMA (Sprint and Verizon) and GSM (AT&T and T-mobile) signals that cellular telephones use.

While CDMA and GSM signals are not inherently bad, it is what happens once the cellular telephone companies get hold of them that makes them so bad.  These technologies exist so that multiple telephone calls can be sent on the same radio frequency channels at the same time.  Your cell phone “shares” time with other users on the same radio channel.  In order to do this however, the amount of information that your cell phone sends out must be reduced so that there is enough room for everyone.  This is what is called data compression.  The idea is that portions of the sound your cell phone receives from your voice is insignificant, and unnecessary to communicate with another person, and in theory, this is correct.

The problem however is that when the information is removed, your brain must contextually replace it as you listen to the party at the other end.  I have noticed two measurable sound quality elements where cellular telephones fall short.  The first one is in dynamics.  Dynamics is the ability to recieve changes in loudness.  Chances are, you have spoken with someone who was shouting into a cell phone and all you heard was muffled noise.  The lack of dynamic range however shows up more in percussive sounds during a normal conversation.  Percussive sounds like “B” “T” “D” or “P” all sound virtually the same when transmitted through a cellular telephone.  It is up to the listener to determine if for example the word “pack” or “back” was said based on the rest of the sentence that person is listening too.  For example, the sentence “I need to back for the trip” does not sound correct, but if you said it over a cell phone, the person at the far end would interpret it as “I need to pack for the trip”  Chances are, you may have even said “Pack” to yourself when reading the sentence…You used brain power to contextually to make that decision.

The next issue with cellular telephone audio quality is in frequency response.  Frequency response is a fancy term for the range of pitches you can hear.  For example, A female voice is higher pitch than a male voice, and a flute has a higher pitch than an oboe.  There is an optimal frequency response or pitch range that is necessary for good clear speech to be heard.  This frequency response is smaller than the range needed for good music fidelity, but is unfortunatley larger than a typical cell phone can transmit.  Vocal sounds that are generated by your voice outside of those ranges are simply not transmitted by the phone, or are distorted.  Again, the phone is relying on context of the conversation to be able to replace what is missing that is not heard.

The problem is, all that work the listener’s brain is performing replacing all the missing conversation data is brain power that is not being used to perform whatever task is at that person’s hand, like driving a motor vehicle.  Analogue FM and AM 2-way radios transmit significantly more sound information, so users of those radios need less brain power to interpret the conversation on those than on digital CDMA and GSM cell phones.

Now  I have been speaking in regards to “perfect” signal conditions when comparing the radio technologies.  If the signal is reduced significantly to “fringe” reception areas, the performance of the different radio technologies differs quite significantly.  When an analogue radio is “at the end of it’s rope” as it is called when it is near the limits of how far it can receive a signal, it will begin to receive “static” or white noise in the background of the received signal.  Most humans however have an easier time interpreting the signal through the background noise than the do when a digital signal is “at the end of it’s rope”.  When a digital signal like what a cell phone uses becomes weak, there is not enough data received to generate sound, so the sound the listener is hearing on a cell phone simply drops out.  The signal may drop large portions of words and even sentences as the signal cuts in and out on a cell phone, prompting the user to say “Can you repeat that, you are breaking up” as they try ineffectively to interpret what the  other party is speaking, and devoting even further brain power off of the road, and onto the phone.

So, there you have it!  Chances are, you have seen someone swerving all over the road while using a phone, or maybe they were completely oblivious to signals and signs while aimlessly sondering on down the highway.  You may have even seen someone pace while talking on a cell phone too.  Now, you know why!  Should we ban cell phones?  I don’t think so, but I think imposing  minimum audio fidelity standards would go a long way towards making cell phones safer.  Imagine how much easier they would be to use if they came through as clear as that big broadcast FM music channel you listen to with the loud car ads?

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