/d/ → /g/
Now the plosive alveolar /d/ is followed by a sound that is produced at the back of the mouth, a velar (a /k/or a /g/), so the /d/ is assimilated into a voiced velar /g/. As you can see, the place of articulation changes, but the manner and the voicing (voiced) are kept.
/d/ (followed by /k/ or /g/) becomes /g/
You should come. ǀ ʃʊg ˈkʌm ǀ
He should go. ǀ ʃʊg ˈgəʊ ǀ
He had very low self-esteem, so he didn’t feel he could go and actually approach this person about what they’d said about him (Theresa Gannon, BBC4).
They showed that the Red Army could contain and to some measure push back the German advance (John Barber, British documentary).
Again, this can happen within a word:
This podcast is supported by advertizing outside the UK (BBC4). /ˈpɒgkɑːst/