The new type of crested gibbon, one of the most endangered primate species in the world, is called the northern buffed-cheeked gibbon or Nomascus annamensis, a statement from the German Primate Centre (DPZ) said.
"The discovery of a new species of ape is a minor sensation," said Christian Roos from the DPZ. "An analysis of the frequency and tempo of their calls, along with genetic research, show that this is, in fact, a new species."
The distinctive song "serves to defend territory or might even be a precursor of the music humans make," the statement added.
The male of the new species is covered with black fur that appears silver in sunlight. His chest is brownish and his cheeks deep orange-golden in colour. The females are orange-beige in colour.
Crested gibbons are found only in Vietnam, Laos, Cambodia and southern China. Scientists had assumed there were six different species but the recent discovery takes the number to seven.
Gibbons have become endangered due to illegal hunting. "Gibbons are kept as cute pets, or they are eaten, or they are processed into traditional medicines," said the DPZ.
Many species number only around 100 individuals, said Roos. Scientists currently have "absolutely no idea" how many of the new species might be alive, but are conducting further study to determine this, he told news agency AFP.
Like orangutans, gorillas, chimpanzees and bonobos, gibbons belong to the apes, man's closest relative.
"Only if we know where which species is found and how many individuals there are can we start with serious conservation actions," added the scientist.
News of the discovery was published in the Vietnamese Journal of Primatology.