Phone Patch

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jthorusen
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Phone Patch

Post by jthorusen » Wed Sep 26, 2018 11:48 am

Greetings to the Forum:

I have been doing some sketching of block diagrams for a phone patch system for a call-in radio show capability. Rather than re-invent the wheel, I'm curious if people out there have preferred methods and equipment.

How does your station implement a call-in interface?

Thanks,
Jim T.
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Shane
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Re: Phone Patch

Post by Shane » Wed Sep 26, 2018 11:38 pm

Usually we buy one.

The Telos line of products is a favorite. JK Audio has some things worth looking into. Used Gentner hybrids are out there and they are good too.

Due to the rising costs and obsolescence - gee, it pains me to say that! - of POTS (Plain Old Telephone Service), many broadcasters are moving to VoIP systems even for studio lines.
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Dale H. Cook
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Re: Phone Patch

Post by Dale H. Cook » Thu Sep 27, 2018 10:42 am

Shane wrote:
Wed Sep 26, 2018 11:38 pm
Usually we buy one.
One major reason for that is that for many years the best hybrids have used digital signal processing on the caller audio, and that is something that you are not likely to be able to homebrew. One caveat about the Gentner hybrids - the digital ones use proprietary ICs. All of the digital Gentners that I have worked with in recent decades have failed to due to failure of those proprietary ICs and Gentner as a company is long gone. If you buy a used digital Gentner its lifetime may be short.
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Re: Phone Patch

Post by grich » Thu Sep 27, 2018 12:27 pm

Dale H. Cook wrote:
Thu Sep 27, 2018 10:42 am
Shane wrote:
Wed Sep 26, 2018 11:38 pm
Usually we buy one.
One major reason for that is that for many years the best hybrids have used digital signal processing on the caller audio, and that is something that you are not likely to be able to homebrew. One caveat about the Gentner hybrids - the digital ones use proprietary ICs. All of the digital Gentners that I have worked with in recent decades have failed to due to failure of those proprietary ICs and Gentner as a company is long gone. If you buy a used digital Gentner its lifetime may be short.
Got a Gentner Digital Hybrid on the shelf downstairs Tango Uniform for that exact reason. :(

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Re: Phone Patch

Post by Dale H. Cook » Thu Sep 27, 2018 3:29 pm

A couple of years ago my last client still using a Gentner digital had their go Tango Uniform so I have none left in the field. I have two of their older analog hybrids still chugging along at client studios.

In recent years I have installed some JK Innkeeper digital hybrids and they seem to be pretty good bang for the buck for stations on a less-than-Telos budget. I've installed a number of Telos hybrids over the last 25 years and have always been pleased with those.
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Re: Phone Patch

Post by NECRAT » Thu Sep 27, 2018 10:21 pm

Dale H. Cook wrote:
Thu Sep 27, 2018 3:29 pm
A couple of years ago my last client still using a Gentner digital had their go Tango Uniform so I have none left in the field. I have two of their older analog hybrids still chugging along at client studios.

In recent years I have installed some JK Innkeeper digital hybrids and they seem to be pretty good bang for the buck for stations on a less-than-Telos budget. I've installed a number of Telos hybrids over the last 25 years and have always been pleased with those.
Call me the absolute odd-ball on this group, but I like the Innkeeper better than the Telos units. I swapped out six dual Telos units for InnKeeper II's at my previous station. The people in the field thought they were clearer, and they worked very nicely for the cost.
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Re: Phone Patch

Post by jthorusen » Fri Sep 28, 2018 1:20 am

Greetings to the Forum:

Many thanks to all who replied. However, I think I failed to make myself clear.... my fault entirely.

If the station were to do remotes, I'm sure a VoIP system would be the way to go. However this application is not for remotes. It is for a call-in as in talk-radio type of show. Thus, it is necessary to interface with a good old fashioned phone line... even though, in this case, the phone is hauled by Spectrum Cable.

The issue is further complicated by the way the station is currently configured.... everything from automation to streaming to audio processing is all handled internally by the software in one computer system. If this were a real radio station as opposed to a toy radio station, there would be separate boxes for automation, audio processing and streaming. Unfortunately, I have to work with what I have for now.

I spent some time thinking about how to do this and I have come up with a remarkably ugly kludge which I think will sort of work.... Please see attached pdf.

KWPB Proposed Phone Patch Block Diagram.pdf
(16.57 KiB) Downloaded 26 times
Let the flames begin.
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Re: Phone Patch

Post by Dale H. Cook » Fri Sep 28, 2018 5:32 am

jthorusen wrote:
Fri Sep 28, 2018 1:20 am
... a good old fashioned phone line... even though, in this case, the phone is hauled by Spectrum Cable.
Then it is not POTS. When we speak of POTS ("Plain Old Telephone Service"] we mean a copper pair, which in many areas nowadays is actually fiber for most of the run. It is not the same as a bit-reduced digital phone circuit, which is what you have.
jthorusen wrote:
Fri Sep 28, 2018 1:20 am
... I have come up with a remarkably ugly kludge which I think will sort of work....
That should work for a single mike, but if you ever want to feed two different sources to the caller at the same time you will need a mix-minus bus. In any case the hybrids we have been discussing, such as Telos, Innkeeper, or Gentner, should work fine. You should have no problem with it being a digital phone circuit because you are not trying to use it for fax or modem. What kind of station is this, an LPFM?
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Re: Phone Patch

Post by jthorusen » Sun Sep 30, 2018 12:37 am

This is odd!

I replied to Dale's question but my post disappeared. If it was removed by a moderator for cause, I'd appreciate a heads-up on exactly why. As near as I can recollect, here is the gist of what I wrote:

Although the phone line is being hauled by a cable company, it seems to me to be of pretty good quality... I don't hear all the digital artifacts I hear on my cell phone... sounds about the same as copper to me. At any rate, that's what they have, so that's what I have to work with.

As for mix minus... that's what I started out trying to design... but it turned out to be impossible. The station board is the first stop in the audio chain.... following it are control of the board's input to the audio mix, automation audio, audio processing and streaming encoding.... all handled by a single computer running SAMBroadcaster and Cirrus streaming software. There are insufficient audio spigots to break out a mix minus from this machine, even if it were possible with SamBroadcaster.... and no one knows if it is possible or how to do it.

So, again, I am constrained by the current equipment and budget. Hopefully, there will eventually be a purchase of StationPlaylist and associated computer power.... but that will shoot more than half of the station's available capital.

As far as the Hybrid is concerned... it is currently envisioned to be a Heathkit HD-15 which can be had for around $40 shipped. The Telos or Innkeeper units are way too pricey.

Finally, to answer Dale's question, yes, this is a low power FM station with a Christian contemporary format: KWPB.

Thanks for all the responses!
Jim T.
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Re: Phone Patch

Post by NECRAT » Sun Sep 30, 2018 8:22 am

jthorusen wrote:
Sun Sep 30, 2018 12:37 am
This is odd!

I replied to Dale's question but my post disappeared. If it was removed by a moderator for cause, I'd appreciate a heads-up on exactly why. As near as I can recollect, here is the gist of what I wrote:
Hi Jim,

1) I just checked the administrator logs for the last 30 days, and no posts were deleted from the entire forum, other than spammer accounts which were also blocked. Clearly you've not been blocked or banned (no reason for it), so none of your posts were deleted.

2) If I or any of the moderators were to delete a post of yours, you'd be given a heads up via a PM. That's the policy here.

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Dale H. Cook
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Re: Phone Patch

Post by Dale H. Cook » Sun Sep 30, 2018 11:03 am

jthorusen wrote:
Sun Sep 30, 2018 12:37 am
Although the phone line is being hauled by a cable company, it seems to me to be of pretty good quality... I don't hear all the digital artifacts I hear on my cell phone... sounds about the same as copper to me.
It may sound the same as copper to your ears but it is not. It is bit reduced, just not as aggressively bit reduced as your cell phone. One way to check for bit reduction is to run a digital compandor system through it - a signal that has already been bit reduced and then converted back to analog, say, a Corex Blue Box or kin. You will not get usable analog out the other end.
jthorusen wrote:
Sun Sep 30, 2018 12:37 am
As for mix minus... that's what I started out trying to design... but it turned out to be impossible.
Without mix-minus your broadcast caller audio will be pretty much useless unless you restrict yourself to airing calls where the caller cannot hear the talent. You are converting between a two-wire system and a four-wire system. You have to keep the hybrid receive output audio out of the hybrid send input, and that requires a mix-minus feed. The common way to do that is to use a second console bus, most often the audition bus, that contains all sources except the caller. The alternative is an external mixer for the mix minus, but you have to have line-level mike outputs for that, either from external mike processors of post-fader sends in the console. Post-fader sends are better as they keep the mix levels set by the faders the same in the mix minus.
jthorusen wrote:
Sun Sep 30, 2018 12:37 am
As far as the Hybrid is concerned... it is currently envisioned to be a Heathkit HD-15 which can be had for around $40 shipped.
Bear in mind that the Heathkit may not be very satisfactory as it was designed for amateur radio use, not for broadcast use. The caller audio may not be of sufficient quality as the receive circuit has no DSP, and the isolation between the send and receive channels will not be as good as a broadcast hybrid.

You wrote upstream "If this were a real radio station as opposed to a toy radio station ..." There are some things that you just can't do in a toy radio station, as they require real radio station equipment. If you want to take broadcast-quality phone calls with a Heathkit hybrid and no mix-minus you are most likely asking the impossible.
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Re: Phone Patch

Post by Shane » Sun Sep 30, 2018 3:46 pm

Two more thoughts for you. Your diagram looks a lot like what we used to do before consoles had mix minus outputs. (BTW, if your console has AUX busses, you can make your mix-minus with one of those, if free, to feed to the hybrid.)

Drawback being that only one microphone can be routed to the caller without mix-minus. (There’s another way to do more than one mic externally of the console but I'll save that.) I see in your diagram you have already taken care of the mic level/line level problem with the mic preamp external to the console.

Instead of a hold coil, we would just answer the phone with the hybrid and the caller audio in cue where we could converse before putting the call on the air, or recording the call for later use. I think how we did the recording was to separately mix the mic preamp out with a mult of the hybrid out and that mix fed to the recorder. That mix could be fixed either with discrete components or a small mixer kept out of sight once levels are set.

I would plug your talent headphones into the console, listening to the total program mix or else the announcer won’t hear themselves nor any other audio they might want to slide under the conversation. Only reason you might need to have ‘phones listening directly to the hybrid output would be if your mixer lacks a cue bus. It’s not normally done today but, in that event, nothing says you can’t have two headphone jacks with the announcer plugging into the hybrid-only output to hear the caller off-line.

Kind of old-timey doing it that way but it worked in the 50’s and 60’s where a local announcer at a network station would have to monitor the network in cue while talking on air so as to know when to bring up the net pot! (And then very quietly move the headphone plug back to PGM.)

Ok, three things! On the hybrid question, having never used a phone patch in 52 years of ham operation, I can’t speak to the question of whether the Heathkit would work but feature this. There is a hybrid in the telephone set.

You can connect to its input and output by way of the handset cord. There are inexpensive devices to help you make use of that option or you could certainly roll your own. Then you already have a pretty good bit of isolation between caller and studio. The only problem might be if the telephone set provides “sidetone” so the speaker speaking into the handset (when connected) can hear themselves as well as the caller. This is done to avoid what we see with many people on cell phones who think they have to shout to be heard! In that case, you’d have to find a way to disable the sidetone in the telephone set.
Mike Shane, CBRE
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Re: Phone Patch

Post by Shane » Sun Sep 30, 2018 3:48 pm

Another BTW. The hybrid we used in that late 70’s/early 80’s scenario was made by Studer. You might find one of those inexpensively. Check with engineer types from local full service stations to see if they might have one they’d let you have free.
Mike Shane, CBRE
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Re: Phone Patch

Post by jthorusen » Sun Sep 30, 2018 5:36 pm

Greetings, All!

Thanks for the replies. For Mike (NECRAT): I'm sure that it was a short circuit between the headphones on my part... I probably forgot to hit "submit" after using the "preview" function. I apologize for putting you to so much trouble.

As to mix minus.... a true mix minus point is buried somewhere inside the computer and SAMbroadcaster software. The best I can do (I think) is about what I have in the drawing. The talent (at least our people) are bothered by hearing themselves with a digital delay caused by the computer processing, so they never listen to themselves on air. With the scheme I have, it will be a normal phone conversation between the talent and the caller with the talent speaking into the studio mic and listening on the headphones. No background music tracks or such available. When the caller is "disabled", then the caller will hear the station air product.... but when enabled, it will be as if it were a private conversation with the talent... except of course, that the conversation is "tapped" and aired.

... At least, that's the way it's supposed to work.... We will see whether or not I have made any horrendous errors when I get it built. And... just as no battle plan survives contact with the enemy, no initial design survives contact with the people who have to use it! :D

For Shane: The Heathkit hybrid is capacitively coupled, so I need an external hold coil to hold up the line. The telephone set in the studio is a low-end cordless telephone... with sidetone.... I think I'd rather not open that particular can of worms.... at least I have a diagram for the Heathkit. As far as audio quality is concerned, as Dale correctly points out, the phone line is already limited; I don't think the Heathkit patch will make things any worse. Of course, all these things are assumptions on my part, and you know about assumptions! :D

At any rate, I appreciate all the feedback.... while I have 30 years of experience as a TV transmitter engineer, I was never into the studio end of things much... and never for radio, so the wisdom here is much appreciated.

By the way, I can supply a block diagram of the whole station if that would be helpful or desirable. It's not much bigger than the one I already posted.

Thanks,
Jim T.
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Re: Phone Patch

Post by TPT » Mon Oct 01, 2018 1:46 pm

Look for Gentner SPH-3's on E-Bay. Analog hybrid, you need to fool with the null for the best rejection of send audio--but probably much better than the Heath Kit. They run in the low 3 figures--one on there now for $125.

Another tip: If you can get the cash, get the ART 351 mono equalizer. Sweetwater, Musician's Friend, BSW, various sources--around $115.
You can't "equalize (flatten out) telephone response that much but it makes a dandy tone control to make the telephone audio sound more presentable.

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