Interface from telephone to computer - options?

[Eusebius]

I want high quality sound from the telephone for making long distance coaching calls. So I want to use a binaural headset and microphone. I could get a seperate headset like the Plantronics ones, but it seems to me that I could just link the telephone to my Mac computer and listen and record (I'd like to record too) etc from the computer, using the headset and microphone I use for Skype already.

Do I need an interface, or is the line in and line out to the telephone just normal 2 volts type line level? In other words I could make a DIY interconnect with just phono plugs for the computer line in/ line out sockets?

All help welcome for this. I can solder connections and am handy with sound equipment.

andy

[Dave Plowman (News)]

I have a dial-up modem which takes a headset and has software for dialling out or accepting ordinary voice incoming calls. That would seem to be your easiest way. However, the quality is restricted by the bandwidth of a telephone circuit. If you want better quality this can be done with a broadband connection.

[Guy Dawson]

Yes.

No. There's usually about 50v DC between the pair of wires that come into your house.

For Windows and Linux systems Dialogic do a large range of interface cards including two port analogue ones. I don't think there's much there for Macs though.

Guy

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[John Weston]

Phone lines aren't the same as "line input"

Don't do what you are apparently thinking of doing. You will ground one side of the balanced phone circuit and this will bring up a ground fault alarm in the exchange, which may or may not generate a fault call for which you could be charged. You need to use an isolation transformer, such as those available from Maplin, etc. e.g.

etc.

Better to get a phone with an inbuilt headset adaptor such as the Plantronics ones you have found.

[Andy Burns]

Use a voice modem, with whatever headset you already have on the machine, I dunno what software exists for this purpose on a Mac though.

[dom]

It's now an older technology, but for super voice quality, no drop- outs, no crackles, no delays - you need ISDN.

I had it for a while when broadband was unavailable here (home highway), data rate nothing special (but reliable and near-instant connection) - but voice calls connect (as afar as you can tell) instantly, with an "in the same room" quality if it's end to end ISDN, and pretty good if it's ISDN to analogue. You also get 3 different numbers you can use, which may be useful.

Not a cheap solution, but if this is the basis of your business, then the additional cost might be trivial to you. However you would need a dedicated line - you can't have IDSN and broadband on the same line.

[fred]

In article , John Weston writes

To add, that one relies on the phone to balance the incoming and outgoing levels (it connects to and requires a handset socket) which is a good idea.

An off the shelf isolating transformer wont match the levels so they are like to be imbalanced and of course wouldn't be approved for connection to the telecom network.

Or a voice modem if driver support is available for the mac.

[The Natural Philosopher]

I've actually got a VOIP router to do my broadband, and second line out from that to my PABX,. Apart from a slight delay in connection, its way superior to my actual voice line, and with the gain turned way up, louder too.

The answer is what I have done. It provides a second line at very keen PAYG prices (no rental charge) at infinitely better quality.

For those interested, its a Billion Bipac 7404 VGP router - a bitch to set up, but works very well and

provide the transfer into the PSTN network.

I even get a number for it that is local to my exchange. That no one can find as its ex just about every directory there is.

[Owain]

However a telephone will be adjusted to provide only sidetone to the handset, not full level outgoing speech.

Really the best option is to use a proper studio type telephone hybrid. If they still do it, the Canford reporter telephone would probably be ideal (canford.co.uk part 98-037)

Otherwise it's a telephone balance unit eg

[Sidney Endon-Lee]

You can, but not in the UK. Germany (Deutsche Telekom) intermixed the two from the inception of ADSL. BT chose not to. It boils down to how much low-end bandwidth the telecoms operator puts aside for either analogue telephony or ISDN. In Germany, many lines were already ISDN, so the ADSL roll-out had to take account of that. In the UK, presumably, BT decided to do otherwise.

See

[fred]

You're quite right, I didn't think that through.

[Andrew Gabriel]

4-5 years ago, I rolled out a private VoIP network across the widespread family members, which we use when calling each other. Just occasionally, someone's ADSL line will be down resulting in a landline call. It's only then that you realise just how terrible the landline is, compared to VoIP we've become used to.

[Dave Plowman (News)]

An ordinary landline with good phones can give decent enough quality. Trouble is people have got used to nasty mobile phones. If you have a suitable computer prog try recording some speech off the radio etc and chopping it into a 300 - 3000 Hz bandwidth. You might be pleasantly surprised.

[Owain]

and nasty digital PBXen

Owain

[Dave Liquorice]

No (noticeable) delays if you use ISDN to carry "3.1kHz audio" or "Speech" but that is telephone quality. If the OP wants better than that you'll be into G722 codecs and the like. They have about 40mS roundtrip which is more than enough to induce a stutter in most people.

[Dave Liquorice]

Quite agree and without the horrendous delay that mobiles have, not to mention the distortion and codec artifacts. I've not been impressed with the little bits of playing I've done with VoIP just as appauling as mobiles but with the added complication of numnerous hoops to jump through to make it work half reliably.

If VoIP can provide a "plug in and use" system that requires minmal or no set up, round trip delays below a few mS (echo cancellation is never good enough), no distortion, no codec artifacts if the connection starts to struggle and better than 300 to 3kHz bandwidth then it might start to rival POTS or ISDN. Oh and I don't know of anybody that I currently call via the PSTN that has VoIP available...

[Eusebius]

Anybody seen this cheap interface from Maplin?

this a true hybrid ?

andy

[Dave Plowman (News)]

The Q&A session is a bit worrying - they talk about ground loops if used with a PC. Twas my understanding *any* connection to the line had to be via an isolating transformer which of course removes any ground issues.

[Dave Liquorice]

No, it's using the hybrid in the telephone.

It's not connecting to the two wire line but to the four wire circuit between the telephone base and the handset. As it causes hum I suspect any "isolation" is just a capacitor and the switch selects which pair of the four wire is connected to the 3.5mm plug. As you say an isolating transformer should cure any hum.

[Dave Plowman (News)]

Ah - didn't read the description properly. Just how many phones use this? Can't say I've ever seen it.