expression, i-adjective
monotonous; flat; lacking intonation
Describes speech, reading, or a voice that is flat and without variation in pitch or expression.
彼のスピーチは抑揚のない声で、聞いていると眠くなった。
His speech was in a monotonous voice, and listening to it made me sleepy.
抑揚のない読み方だと、内容が伝
If you read in a flat way, the content is hard to get across.
単調 is a more general term for monotony in rhythm, pattern, or routine, while 抑揚のない specifically refers to lack of vocal modulation.
Phrase composed of 抑揚 (intonation, modulation) + の (possessive particle) + ない (negative form of ある). Literally 'without intonation'.