"Degrading" Quality of a Recording

[ukrwebguy]

[Windows 10]

So, I'm working on a website to teach the French language. The website has dialogues of different speakers, and I asked my friends (who live in different cities) to record their voices for the different parts, which I then spliced together into the same audio file. The problem is that the audio is of different quality of each of my friends is different. For example, one was recording with really good audio equipment in a silent room, and others were basically just sitting in an apartment with a smartphone microphone.
Could someone listen to the file that I've attached and let me know if there's post-production editing I can do on Audacity to make the different speakers sound more "similar"?

https://drive.google.com/open?id=0B9mYV ... 0kxdjJQdTg

In the above file, one speaker just sounds a lot higher quality than the others. If I can't make the other speakers' recording quality match the quality of his recording, I'd like to "degrade" that speakers recording so that it matches the others. Any help and suggestions would be appreciated.

[Trebor]

A quick fix would be to re-sample the entire track to 16000Hz that degrades the the good quality recording, making it less conspicuous.

A time-consuming, but more precise correction, would be to change the equalization of each instance of the the good quality (Marcel) to match the smartphone (John) using the equalization curve "D2" below ...

''dialogue-fr-06-00'' Before-After ''D2'' equalization applied to only to Marcel.flac

(1.44 MiB) Downloaded 12 times

''D2'' equalization curve (Marcel only).png (47.63 KiB) Viewed 143 times

D2.xml

The data for the "D2" curve , import into Audacity equalizer.

(17.79 KiB) Downloaded 8 times

http://manual.audacityteam.org/man/equalization.html