Heavy clipping and whole frequency band missing

I just bought a landline recorder so I can review some of my phone calls. Although the recorder does its job, the quality of the recordings is quite poor, mainly due to heavy clipping. I only want the recordings to understand what’s being said, and that much I can do, so the thing serves its main purpose, but it’s quite unpleasant to hear all that clipping.

The recorder is quite basic, and apparently it’s not possible to set it up to record at a lower volume. I’ve been fiddling a bit with Audacity but haven’t managed to improve the quality of the recordings. The Clip fix effect doesn’t seem to help. Something that has surprised me (maybe just because of my lack of knowledge about audio waves) is that three band frequencies are missing altogether, roughly 1650-1750 Hz, 2750-3650 Hz and 4600-4800 Hz:
Missing frequencies.png
I might buy a better quality recorder in the future, but for the time being I’d just like to know if there’s some easy way to improve the quality of these recordings.

I attach a sample of one of the recordings.

Windows 7 Home Premium SP1
Audacity version: 2.1.2

I might buy a better quality recorder in the future

You may not need the whole new recorder. I use Olympus TP-7 and TP-8 special purpose microphones (in my ear) and plugged into any Mic-In. Of course, Olympus would love you to plug it into one of their recorders, but I use a little headset adapter and plug it right into a computer.

I record and export the sound files in Audacity.

Once you clip audio, that’s the end of the story. Clip Fix is for the occasion where one brief sound or vocal expression goes a little over. It will not turn ten minutes of burning devastation into clear audio.

I actually have an Olympus recorder and I should really try this in the field. There’s no reason it would not work with a cellphone on the street except for RF interference.


I don’t think that helps in this case. This is a landline recorder which connects directly to the phone line. If Audacity can’t help to improve the audio quality, I think that’s the end of the story. Still, I post a few pictures of the recorder to clarify just in case:

And a link to the recorder’s manual (in Spanish): http://www.tecnipanacol.com/#!grabar-llamadas/c250o

To improve the current recording:

  1. Import the recording into Audacity
  2. Normalize to -1 dB (see: http://manual.audacityteam.org/o/man/normalize.html)
  3. Open the Equalization effect, select the “Telephone” preset and apply (see: http://manual.audacityteam.org/o/man/equalization.html)
  4. Export as a WAV file (don’t reuse MP3 because the recording is already bad and MP3 will only make it worse.

Long term, you really need to look into alternative ways of recording. Koz as posted some quite impressive clips using the equipment described in his previous post.

I use it on a landline. It’s not going to work if there’s no human speaking on an actual phone. Is there something magic about what you’re doing? I use it to remember what time my dentist told me to be there.


That was awesome. Great quality improvement! The quality is still poor, but the sound is not annoying anymore. I will definitely get a better device in time, but in the meantime this is sweet. Thank you!

One more question, though. Is it worth fiddling with the equalization values to improve a bit more the quality or is this close enough to the best you can get?

I’m not following. Of course there are humans on both sides of the line. I use this for very mundane things too. The recording I uploaded is a conversation between myself and a librarian about how to request a book.

How do you use that speaker-microphone with a landline? Do you connect the speakrophone AND a recorder to the landline?

I plug that special purpose microphone into the Mic-In of whatever computer I decide to use. I have an old laptop with a partially broken screen. It’s not much good for anything else.

I jam the microphone part into my ear (the ear part is adjustable). Start Audacity, start recording and announce the time and date. The sound meters and blue waves will react to my voice if everything is set OK.

This is a live recording, so you have to make sure the speakers are turned off.

Pick up the phone and use it on the same side of your head as the microphone. Dial. Talk.

Hang up. Stop Audacity and File > Export. That’s exactly how I made those two clips. The originals were much longer.

This works with any phone. No wiring. It works with cellphones, too, but there I get a little whistling because of radio interference. There maybe a way around that. Any second now I’m going to get to that.

The graduate course is not use the computer at all but plug it into an Olympus sound recorder like it was designed. The cellphone, recorder and microphone will fit in one pocket, and depending on the recorder, can do a terrific job as environment recorder as well.

“Tell me again how to get to the Tesco/7-Eleven? Down Wilshire and turn…right is it on Westwood?”