Jason

Guest Post: The Deaf Use the Phone?

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UPDATED: March 29, 2016 Title has been renamed to reflect the original submission.

I received a submission of a guest post from Jason from Montana, edited by your humble curator kinda out of the blue. I did a pretty brief post on TTY a couple weekends ago and was surprised that I’d get a response, and got more insight to the TDD use of TTY. I’ve been meaning to post this subject for a while. Anyways the rest of the post is from him.

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Yup, it’s true, the deaf can use the phone. And ironically, they’ve been able to for many years.  The Telecommunications Act of 1982 “allows states to require carriers to continue providing subsidies for specialized equipment needed by persons with impaired hearing, speech, vision, or mobility”.

 The TTY device introduced in the 1970’s used the Baudot protocol to transmit text over standard telephone lines.  They’re actually primitive modems in the sense that TTY’s use Frequency Shift Keying to have a tone match the character typed on the keyboard.  Baudot runs very slow by comparison at only 50 baud.  Most TTY’s have a character buffer so one can type faster than 50 baud, and the TTY will transmit as fast as it can. For someone who types 120 wpm, reading or typing a TTY conversation is painfully slow.  By comparison, excluding compression, at the end of the dial up internet era most modems could do 56k, or 56000 baud.  On the other hand, the phone lines don’t need to be very clean or clear to keep up with Baudot.  Also, the conversation was simplex, meaning only one party could communicate at a time. TTY didn’t have any advanced algorithms to enforce this, so it was up to the users to clearly delineate when they were done typing by using the phrase SK (stop keying).  This Wikipedia article (use with caution) has 3 fairly believable sample conversations.

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Telephony in Radio Broadcasts, part three

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Jason, the guest writer on Avaya’s SIP agenda, has kindly given me some stuff to post while I’m out of the office at the Museum of Telephony. This is the last installment of this series.

Some technologies I never used:

 Other larger stations would use ISDN directly to the hybrid.  It’s my understanding that this is like presenting a PRI directly to the hybrid with no front PBX. It was stable, and the audio quality was as good as the CO’s switch.  In these cases, the caller’s analog or cellular connection was often the limiting factor for audio quality.  I would imagine these are the type of systems used by the big talk show hosts like Glenn Beck or Rush Limbaugh.

 Remote broadcasts in other markets are moving to a full internet based VoIP solution, where the remote broadcasters has a unit that speaks IP to the nearest internet connection and negotiates a VoIP “call” to the dedicated hybrid at the studio. I’ve even seen apps for smart phones that allow this style of connectivity using the phone’s hardware to do the VoIP work and the cellular data network for the data. I’m not sure I’d want to try this in a mission critical application!  On the other hand, it’d certainly sound better than a raw cellular call and doesn’t have the hassle of setting up a microwave link.

 In the studio, if SIP is king, Hybrids are available to consume SIP audio just like an IP phone.  I would imagine if you have good SIP trunks these sound delightful!

 There you have it.  Telephony meets Radio.  I think so long as radio is around, you’ll continue to have talk show callers, contest callers, callers who want to know the weather.  Despite the push to the Internet, telephony is still the preferred method for many radio listeners to communicate and have a voice in their station, no pun intended!

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Telephony in Radio Broadcast

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Jason, the guest writer on Avaya’s SIP agenda, has kindly given me some stuff to post while I’m out of the office at the Museum of Telephony.

Names have been generalized to protect the innocent.

 I’ve worked for two different radio companies in my employment history. With my interest in telephony, naturally I was interested in how the telephone callers got “on the air.”  Here are a few case studies on radio telephony that I’ve experienced.

 A quick definition for the un-initiated: In the radio business, a telephone hybrid is the piece of equipment that translates telephone audio (normally standard analog) into balanced signals to feed the audio console and does some active nulling to prevent too much of the announcer’s voice (which goes directly on-air via his microphone) from returning via sidetone on the telephone circuits.  A technical demo of a Hybrid

https://www.youtube.com/watch?v=k6k4gS-gkC4

 How not to do radio telephony:

The first company I worked for was a small two station cluster.  Its engineer was of the mindset, “Let’s not buy the correct equipment, I can do it just as well with parts from Radio Shack and some creative circuitry!”  For the purposes of this case study, I will ignore the second station which was fully automated and used a single line Gentner on a dedicated CO for any telephony on that station.

 The other station had an on-air studio, and a production studio. As you can imagine, the on-air studio ran the live broadcast, while the production studio was used to record content, commercials, shows, and other audio to broadcast later.  The entire company was served by a Comdial key system with 3 CO lines.  The Comdial functioned on 4 pair wiring, with the outer pair providing signaling, and the inner pair presenting as a standard analog line to each station, switched according to the buttons on the handset.   Both studios shared one Symetrix TI 101 Hybrid, whose “line” was selected by an ordinary low voltage DPDT switch. To use the system, you would grab the incoming line on the handset, and it would be automatically coupled to the Symetrix according to if the switch was set to On-Air or Production.  The Symetrix bridged onto the center pair of wiring going to each telephone, so whatever line on the set was selected, that’s the line you got on the Symetrix.

 Feedback elimination was crudely accomplished by a switch drilled into the telephone base which cut off the wiring from the telephone microphone. So when you were ready to put a caller on-air, you’d answer the call, get the caller ready on the handset, flip the switch, then talk to them using the on-air microphone, fed via the Mono bus on the console. As hybrids go, the Symetrix was about as basic as they came, with all parameters being controlled with knobs rather than with fancy automatic gain control.  Did I mention that the Symetrix was in the production studio so it was impractical to make real time adjustments to an on-air caller?

 Ringer muting when the mic was live was also accomplished manually in each set by a relay that cut off the speaker in the set.

This station also had one other funny quirk.  When a local vendor discontinued their satellite feed of the local sports roundup, we solved the problem in a most low-tech fashion.  Shortly before the roundup was to air in the morning, we’d call the station and ask the secretary to put us on hold. Then, we’d record the roundup off their hold music!

 If you needed to have something from the telephone live on-air and record something else, you were simply out of luck!   As you can see, this is how NOT to do radio telephony.

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