In Russian, as well as in all other languages, consonants are either voiced or voiceless. Consonants that make your vocal cords vibrate when you pronounce them are voiced, and the consonants which don't are voiceless. If you don´t feel the vibration you can make a little test: touch the area of the throat while making this sound 'z-z-z...' and then make this sound 's-s-s...' and you will feel the difference.
Most voiced consonants in Russian are paired with a voiceless one. The consonants in each pair below are pronounced in exactly the same manner, the only difference being in the presence or absence of vibration of the vocal cords.
|Unvoiced||п||ф||т||к / x||ш||с|
Voiced consonants at the end of words are pronounced like their voiceless counterparts. In Russian it is called devoicing of consonants.
The change from voiced to voiceless also happens when voiced consonants precede a voiceless one.
For example, in the word завтракать (to have breakfast) the voiced consonant в is in front of the voiceless consonant т. Here the pronunciation of в will assimilate with the pronunciation of т; both will be pronounced voiceless therefore we pronounce ф instead of в.
Voiceless consonants before б, д, г, ж, з are pronounced voiced.
Always keep in mind that when you have a pair of consonants, it is the second consonant that determines how the first will be pronounced.
Before к and ч pronounce г as х:
The combinations of сч, зч, жч are all pronnounced as щ:
The combinations of сш, зш are all pronnounced as шш. The combinations of сж, зж are pronnounced as жж.
The consonants р, л, м, н, й don't have voiceless counterparts. When one of these consonants is preceded by a voiceless consonant, the voiceless consonant is not affected and pronounced as it is.