listenning two SSB stations, one shounds like donald duck

Hi, there are many times when listenning a conversation between two HF ssb stations from different locations (DX). I tune to the first station and the sound is natural. However the other station sounds a bit like donald duck.

This sound is common to SSB radio when the RX frequency is not exactly tuned to TX.

However, in the case above, why one station is listened ok and the other like donald duck?
Is it because one of the hams is not exactly tuned to the other's frequency, or is it some kind of ionospheric distortion?

Most likely it's tuning errors but technically, although it would be unusual, there is no reason for the two station to use the same sideband. Quite likely one of the stations has accidentally left an "RX offset" (RIT) turned on so their transmit and receive frequencies are slightly apart.

Brian.

Ok so it is all about non accurate tuning in each case. It is not related to any kind of ionospheric, distance or other factors that cause this.
Thanks a lot

It's a well known effect of having a slightly off oscillator somewhere.