telephone recording

[mick scott]

Can I use audacity to record a telephone interview from a landline? What Hardware do I need?

[steve]

Probably the easiest way is to use a speaker-phone, then place a microphone so that it picks up both your voice and the speaker. The other persons voice will be way below "broadcast quality", but I think broadcast quality requires some pretty heavy duty (expensive) equipment. There's plenty of other methods, so perhaps someone else will chip in (Koz?)

[zs6ro]

Can I use audacity to record a telephone interview from a landline? What Hardware do I need?

For casual use one could use a 1:1 600 ohm transformer across the telephone line. This would isolate the telephone line voltages from the mixer/sound card line input and reduce hum and other nasties.

If the transformer is physically very small, the line voltages may saturate the transformer core causing distortion. To prevent this, a 2.2uF non-polarised capacitor is placed in series with one leg of the transformer going to the telephone line. For more permanent use, lightning protection devices should be added.

Another method would be to take a seperate telephone and remove the ear-piece (receiver) and fit an audio transformer in it's place. Then take the free ends of the transformer and fit them to the relevant line-in on the sound card. The modified telephone is placed across the telephone line, in parallel with the existing telephone instrument. Don't forget to take the modified telephone handset off the cradle when recording. It might also be a good idea to remove the microphone (transmitter) as well to stop external acoustic noise entering the system.

Once the call is captured, Audacity can be used to level the audio of both sides of the conversation.

Of course the telephome company may frown on foreign 'objects' being placed on their lines !!

Richard

[kozikowski]

So the short answer is not easily. The phone company plays a lot of tricks to get voices to go both ways on one pair of wires at the same time. Radio Shack used to make simple, cheap phone couplers, but the universal complaint with those was the near voice was always far louder than the voice at the far end, and there was no way to separate them.

Still isn't. Doctor Laura, Car Talk and the other talk-shows use expensive Telephone Hybrids to make the shows sound like that. Thousands of dollars.

If you have or know somebody who has Skype, you can use the upper two licenses for Pamela, Business and Professional, to record both sides of the conversation on different tracks so you can edit them later and fix bad sound levels.

http://www.pamela.biz/en/

Koz

[kozikowski]

There is also a way to break into a cellphone and do this, but this puts you back in the 'solder parts together' group. Amateur radio operators and other electronics enthusiasts have been doing this for years, but I don't know that the regular computer user would be up to it.

Koz

[zs6ro]

Good point Koz, yes, radio station talk shows do use sophisticated hybrid equipment ... It is a complicated affair to get the studio mike interfaced into the telephone line and get the caller's voice modulating the radio transmitter, all without audio feedback and howling taking place and still maintaining correct audio levels all round .. If i recollect usual hybrid circuitry allow about -25dB seperation on the 4-wire side which isn't much and if iine impedances change, that -25dB balance suddenly becomes a lot less .... (The -25dB is made up from a transmitted -17dB and a receive level of +8dB on the 4-wire side of the hybrid - may be different in other parts of the world.)

Most telephone apparatus nowadays have some electronic circuits in them which do quite a good job in keeping audio levels relatively constant. It is possible that modding and connecting it the way I suggested, 'might' level out the near and far end speech reasonably well to do simple post processing on it afterwards ...

Granted it would be ideal to have a track for each voice like in Pamela/Skype.

Anyway, I would suggest experiment and see what happens .......

Richard

[billw58]

No need to tie into the 4-wire line anymore:

http://www.jkaudio.com/innkeeper-pbx.htm

I'm just posting this link to show that it's possible to do this by patching into the handset cord with the correct support electronics. I'm not suggesting anyone here would be likely to buy it at the price. It's still tricky to set up, despite the hype on the site.

-- Bill

[steve]

I'm not suggesting anyone here would be likely to buy it at the price. It's still tricky to set up, despite the hype on the site.

That's the "affordable" version, and still a lot more than one of these http://www.pcwb.co.uk/catalogue/item/BT ... dp=Froogle with a microphone near it. I would not be expecting a great sound from this cheap-as-chips method, but for occasional home use it would probably be adequate.

[zs6ro]

Interesting links .....

One could use a telephone instrument and remove the handset capsules and fit isolation audio transformers and feed into the sound card ... (could then send audio files down the telephone line!) .. Simple way to get 2-wire to 4-wire ...

The problem with this of course is the designed 'sidetone' which is always heard in the receiver side of the handset when the near-end user is talking .. One would have to dig around on the circuit board to try and reduce the sidetone further ..

But I digress ...................

Richard

[kozikowski]

<<<The problem with this of course is the designed 'sidetone' which is always heard in the receiver side of the handset when the near-end user is talking>>>

Yes, The device is only as good as the network inside the phone and that's been intentionally unbalanced slightly to produce sidetone so it doesn't sound like you're talking into a bar of soap... or a candy bar... or a cellphone. But not good when you're trying to do production on the phone. Skype/Pamela is the grand champion of solder-free telephone production. The lower two licenses of Pamela will capture your conversations OK, but will not separate them into two different tracks. If one person is a lot lower than the other, that's life. Have a happy day. So one of the two upper licenses is indicated.

We haven't heard back from the original poster. Think he's recoiling in horror?

Koz