"There are some sounds that English singers find quite difficult to manipulate"

This quote by Neville Marriner is describing the difficulty of English vocalists to manipulate particular noises. This could be referring to the difficulty of English singers to properly produce particular noises that are not native to the English language. For example, English vocalists might discover it challenging to precisely produce the sounds of certain foreign languages, such as French or Italian. Furthermore, English singers might discover it challenging to accurately produce certain noises that are not generally discovered in the English language, such as particular vowel sounds or specific consonant sounds. This trouble is likely due to the reality that English vocalists are not used to producing these noises, and thus have problem manipulating them. Ultimately, this quote is a reminder of the problem of English singers to properly produce particular sounds that are foreign to the English language.