recording telephone conversation

[Philip Fass]

I told a client I'd look into equipment for recording a phone conversation. It would be a single-line landline phone going into a PCM-D1 (3.5mm line input) or into my Mac Pro. So far I've thought about these:

http://www.bhphotovideo.com/c/product/380766-REG/Rolls_PI9_PI9_Phone_Patch_II.html
http://www.bhphotovideo.com/c/product/284517-REG/JK_Audio_VOICE_VOICE_Telephone_Handset.html
I suppose I could also use my HPX370 to record audio through XLR.

The two above are low end, and the Catch-22 I have is that I want the interviews to sound good, but there will only be 2 of them, so I don't want to over-buy with this thing.

Any thoughts on these or alternatives?

[Greg Miller]

Do you need to record both sides of the conversation, or just the distant end?

[Philip Fass]

I could have them start each answer with a complete thought, so I don't need my questions.

[Greg Miller]

The absolute minimum cost approach involves three issues:

1.) the telephone has a "mute" button and the nature of the call allows your local talent to use it,
2.) you're enough of a tinkerer to open up the telephone and connect a few wires,
3.) you have access to an audio isolation transformer, or some sort of transformer-based direct box.

If this approach is applicable and you want to try it, I'll describe it. If this doesn't suit you, then there's no point in my going into the details.

[Philip Fass]

Greg, I really need an off-the-shelf solution, but wanted some help finding the best compromise of sound quality and cost.

[Shaun Roemich]

I believe this is what you are looking for:

http://www.bhphotovideo.com/c/product/333892-REG/JK_Audio_AUTO_AutoHybrid_Telephone_Audio.html

[Greg Miller]

OK, we'll rule out a roll-your-own solution.

To do a really good job recording both sides of a two-way call you need a device with a balanced hybrid. The item Shaun found seems to be such a hybrid device. However, you don't need anything that complex (and expensive) to record only the distant end.

Both of the devices you found seem quite minimal, and they don't appear to have a hybrid circuit. Nevertheless, they will probably work OK for your application. Just be sure to use the mute button on the local telephone, because both of those interfaces will probably pick up the near-end audio (which you don't need) and that will probably be significantly louder than the far-end audio. So be sure the talent at both ends is aware of this limitation. After the near-end talent asks his question, be sure the far-end talent waits a second or two before answering, so the near-end person has time to mute his mic.

Note that these are probably designed for a conventional two-wire analog telephone system. They probably will not work with a digital multi-line system such as those found in a lot of office environments today.

If you do want to capture the near-end questions, record those with a good, local mic, and NOT over the telephone system; then inter-cut the two tracks A-B roll fashion.

When you are processing the audio afterwards, be aware that telephone audio usually contains nothing below about 300 Hz. So if you hear some hum on the line, you can start by using a 300 Hz low-cut filter to get rid of it.

(And of course you want to be sure the far-end talent does NOT use a cellphone, because those always have terrible audio.)

[Richard Crowley]

This might be worth a try for a really low-budget, limited-use project:

Olympus Mini Tele-Recording Device - RadioShack.com

[Greg Miller]

That Olympus gadget appears to be a small [outward-facing?] mic which you place in your ear! It then picks up the acoustic sound from the telephone earpiece. Of course it will pick up other acoustic noise, too, and I'd expect it to be sensitive to the positioning of the telephone earpiece relative to the gadget.

With all due respect, I'd be very afraid of something like this. A direct wired connection should be much better.

[Philip Fass]

To keep things simple, I'll probably choose between the two items I mentioned. The less expensive has a 3.5mm output for connecting to a recorder. The more expensive records to a computer.

Is one inherently better than the other in terms of sound quality? If not, I can live with transferring the files from recorder to computer.

[Greg Miller]

The first device (from Rolls) clearly has normal analog audio connections. It will work with a recorder, mixer, or can use the analog connections on a computer's sound card.

Note that it works only with single-line analog phones... apparently it plugs into the line jack.

The second device (from J/K) also has normal analog audio in/out jacks. It says it works with a computer sound card which confirms that it's analog, so it will work with any analog audio mixer, recorder, etc.

Note that it connects inline with the telephone handset and not the incoming phone line. Thus it will work on multi-line phones (as well as single-line phones) if they use a standard handset connector.

[Andrew Bove]

If you're willing to use an smartphone, there are many apps that do this easily.

[Don Palomaki]

For a one-time (ot two) thing just record a speaker phone using a conventional mic, if that gives you sufficient quality. Be sure all parties have appropriate privacy warnings before you record. You could make that phone an extension in a different room and mute its mic. Potentially nothjng to buy.

[Jim Michael]

Another option is to outsource the recording to a service such as a conferencing system. Typically you will get something on the order of a 16 or 8 bit 8 kHz audio file. I forget the frequency range. Not quite as good as having at least one side recorded with a decent recording device.

[Greg Miller]

Originally Posted by Don Palomaki

just record a speaker phone using a conventional mic, (snip) You could make that phone an extension in a different room and mute its mic.

If you record from another phone in a different room, you will experience large difference in levels. The "near end" level will be very much louder than the "far end" level. This will entail lots of extra work in post. And any small noise at the near end (rustling of paper, coughs, etc.) may well be louder than the audio coming in from the far end, making the desired audio unintelligible; there would be no way to fix that in post.