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Okay so I have a couple reasons why I need to record a phone:

1) To get an authentic phone futz signal for a film where some dialogue needs to sound like it's on the phone.

2) A radio show I record has callers call in as guests and I need to record them.

I have a jerry-rig to record the phone which also unfortunately records the signal you send to it (i.e. the radio host talking to the person) so I get the radio host and the phone guest and there is no way to separate the 2 signals to record them separately, which is what I want.

I searched for what they use in radio stations for this type of thing, and they are all like 3000$ and up for a box to do this with.

Does anyone know how I can record the phone signal clearly and separately from the outgoing signal from my end?

Oh and as a note my studio has digital phone-lines... I know that throws a wrench into some of the plans.

Thanks!

  • Ryan
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    Not an answer as such, so I've added it as a comment: Ryan, check with your facility IT folks. If you have VOIP phones, you can do all sorts of cool hacks with such phones on a LAN. You might want to look into a telephony app on the desktop, and then just record the incoming call using your DAW or audio utility of choice. We have an open-source VOIP solution at work, and I can route calls into Audio Hijack Pro if needed with a desktop calling app. Also, don't forget to look into using Skype! [Both of these would indeed require futzing in post - Speakerphone seems to be the way to go there.]
    – NoiseJockey
    Commented Mar 28, 2011 at 2:07
  • @NoiseJockey Hey! Thanks! Glad to see you're still around!
    – Utopia
    Commented Mar 29, 2011 at 1:36

8 Answers 8

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I´m afraid that feedback is an inherent effect to analog telephone lines. It is because of the hybrid transformer used to convert the 2 wire side of the line to the 4 wire side. Most of pro hybrid adapters can be adjusted to avoid this effect, but this equipment is quite expensive. We have some of equipment of this kind here that haven´t been used since we started working with ISDN lines, which leads us to the digital era.

Basic digital telephone lines work at 64kbps, being sample rate equal to 8kHz and wordlength equal to 8 bit. Codification follows A-Law in Europe and mu-Law in other countries, contrary to our common linear PCM files. These are said to follow the G.711 protocol, wich we use for incoming calls in breaking news or intercom in OB vans. An improved method is used when quality is an issue that is called G.722.

You won´t find any problem to encode your recordings to with this specifications, at least for the first one. Some PC based apps will give you A-Law or mu-Law options when going to export a sound file.

You may try to apply a low-pass filter with cutoff freq at 4kHz too, it´s worth the shot.

If not, you may give Speakerphone a try.

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1) if it has to be authentic i won't tell you to use a normal voice recording and pass it through a bp filter 2) you can try to hack those cheap speakerphones. Reach the loudspeaker and connect a mono cable (may be you'll need to solder it) with the jack you need to connect to your mixer/recorder/pc...

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  • Be VERY careful doing this... Even battery-powered kids toys often have super-hot signals going to the speakers, and if you're not careful, it could cause damage to your equipment. Since it's mono, use a cheap guitar pedal (without true bypass) as a buffer -- almost anyone you know that plays guitar should have at least one laying around.
    – Dave Matney
    Commented Sep 6, 2010 at 21:48
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There is a telephone mic that you can use to record phones although not the best looking of sorts. You can stick it to the speaker portion of the handset(next to the ear) to record the output. I haven't used it that way as I use the mic for other purposes but that is apparently what it was designed to do.

Telephone Microphone

This would help get the sonic quality of the phone as well, comparing to tapping the phone line.

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re 1) do check if the director is really after authentic phone sound and also the perspective they will want (e.g. a cellphone sounds very different from a distance than when pressed against your ear). v.likely they will want it more intelligible than authentic.

re 2) this won't win any awards for being straightforward but surely a couple of minutes researching skype-in can't hurt?

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  • @georgi Hey thanks for replying! Wow that's a good point about the perspective... I was going to use it for a 911 emergency call for a commercial. Re: Skype - I tried it already and it doesn't sound as clear and as good as a landline and it drops out frequently.
    – Utopia
    Commented Sep 6, 2010 at 20:03
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Do you think you'd have the possibility to use two phone lines, an incoming one for the callers and an outgoing one for the radio people?

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It's about $500 list price, but you could check out the Inkeeper PBX by JK Audio: http://www.jkaudio.com/innkeeper-pbx.htm

Seems like it would do what you need to do. We use it for phone patches where the producer is in another city/traveling and it works pretty well (we have digital lines here too).

Additionally, I've used it to worldize some dialogue for a short film...

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I used a gadget called a "THAT" also made by JK Audio. I had mixed results, but it was pretty cheap. Even tho it only had a couple of knobs (input attenuators) i found i had to fiddle with it a lot. For the price it is ok. Used it for remote VO recording sessions.

David Rovin

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Izotope Decrackle has a cellphone preset, you could output the crackle from that.

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