attempted phone recording - ultra-faint signal


I’m using a RAdioshack recording connector into my mic jack and despite fiddling with the Windows recording control, trying Microphone, rear mic, and line in volumes (and slider on Audacity), the signal is almost a flat line. (searched the forums but couldn’t find a solution).

If this helps the diagnosis at all, when I put a cable from my headphone jack to the mic jack (recording a flash audio file from the web) the signal strength is great in Audacity. Also, using the same RAdioshack device with my Olympus digital recorder gives acceptable signal strength. I would like to bypass the recorder and go straight to the PC, though.

What should be my next step?


Check if you are actually using a “Mic” input or a “Line” input. Microphone inputs are considerably more sensitive than Line inputs (and will usually distort badly if you feed a signal from a headphone out).

You haven’t actually said what you are trying to record - is it a microphone?

I’m trying to record telephone interviews, so it’s the gizmo that you connect between the phone and the phone line and has a plug that goes into the mic jack of the PC.

I’ve tried both mic and line in in the dropdown box in Audacity and neither do more than almost-flatline.



A little known problem is the Audacity graphic flatlines at about -36 which is well within the range of human hearing. So just because Audacity doesn’t give you a blue-wiggly line, doesn’t mean there’s no signal there.

Welcome to the problem everybody has trying to record a phone conversation. One electrical problem that the cheap phone devices have is they don’t even try to compensate for the dramatic level changes between outgoing and incoming. Actually, the cheap ones can’t tell which direction the sound is going. It’s not unusual for the incoming to be mic level (reeeely tiny) and the outgoing (your voice) is close to line level.

I also wouldn’t be surprised to find that your little voice recorder has dynamic level compensation which can help a lot with this. Audacity needs to do all that in post.

What happens if you select a bit of the existing far voice and apply the normalization filter? Make sure just the far voice is in this test.

You can mess with this until the cows come home–or even well after–but a really good work-around is to put a microphone next to a speakerphone and call the other person. If you do this in a really quiet room and get close to the phone, you should be able to get a very respectable recording. It doesn’t have to be a big honkin’ microphone, either. This Radio Shack should do it just fine:


Oh, one other note. You can use Audacity to help you troubleshoot. If you open Audacity and click once inside the red record meters, they will wake up and tell you the incoming volume without going into a full recording session. Those meters do go way, way down and measure very quiet sounds.


Thanks Koz,

I’ll check that out. I don’t want to go the speaker phone route, so i’ll check that out. Otherwise I’ll stick with my digital recorder and accept that it will take an extra set. Is this something an inexpensive mixer would address (i.e. amplify the signal strength?


<<<Is this something an inexpensive mixer would address (i.e. amplify the signal strength?>>>

Messin’ with phone lines can be interesting. If you happen to be holding that red-green pair of wires when it rings, it will give you a shock. Ringing current is strong enough to physically move the bell clapper inside an older phone. It’s also strong enough to make you throw your Starbucks across the room. And then there’s the business of the 48 volts which every phone line has. Don’t stand in water while you’re holding them. That’s the main reason for the Radio Shack device. To prevent the 48 volts from entering the audio chain. It may deal with ringing current, too. What’s the part number of the one you got?

A hybrid amplifier would do it.

Those extensively process the phone audio and can tell which direction the audio is going. It gives you the near audio and the far audio and level corrects each one. It give it to you on separate wires so you can record them on different channels–say left outgoing and right incoming.

Past that, you need to deal with the fact that no matter what you do, the far side audio is never going to be more than a small fraction of the volume of you at the near side which limits what you can do with straight audio amplifiers. Also remember that the sound is traveling how many miles on unshielded, open-air wires. Anything you do to upset the balance is going to start humming and buzzing.

<<<I don’t want to go the speaker phone route>>>


People think this is a simple process. Audio on a phone line is a college level course. Speakerphones have a lot of this audio processing built-in.