The censorship of music with controversial content is a threat to the future of music around the world, a top African singer has warned.
Mapfumo's music has been banned by Zimbabwe's government
Zimbabwean musician Thomas Mapfumo, who moved to the United States after his music was banned by Robert Mugabe's government, said he feared musical talent was being repressed like never before.
"They can't stop me from recording my music, but they will do that to up-and-coming musicians, like youngsters," Mapfumo told BBC World Service's The Music Biz programme.
"If they try to record a song like mine, they will be told they are not allowed to record in any studio. That's depriving those youngsters."
'Voice for the voiceless'
Many countries around the world, including the US, censor music in various ways, according to the Free Muse organisation, which advocates free musical expression around the globe.
Censorship is particularly severe in a number of developing countries, where music can have a big impact on those who hear it, they say.
"We in the west talk about the printed press as so important - that's how we get to know things," said Free Muse's executive director Marie Corper.
Music in North Korea is only considered worthwhile if it praises the leader
"Especially in those countries where the written word is not that important - countries where people can't read and write - music and radio is the mass media."
She said musicians such as Mapfumo saw themselves as a "voice for the voiceless".
Authorities use a broad range of techniques to suppress music they feel threatens their power, she said.
In Mapfumo's case, various tracks critical of Mugabe have been banned.
"Every piece of music that is critical of the government is not allowed to be played on the radio," he said.
"Whoever criticises the government is an enemy of the state. That disturbs me a lot."
In Mexico, a street singer named Andreas Contreras says he has been physically threatened by police because his lyrics include praise for Osama Bin Laden.
Contreras is a supporter of the Zapatista uprising and supports those who have damaged what he sees as Mexico's oppressor, the US.
In the US itself, there are certain forms of censorship, Ms Corper said, such as music imports from Cuba.
And the Federal Communications Commission (FCC) has the power to fine radio stations that play records it considers "indecent".
Restrictions on music were lifted at the end of the Taleban rule
In one case, singer Sarah Jones found she had been restricted because her song contained the lyrics "your revolution will not happen between these thighs". She appealed against this decision and won.
Rap singer Eminem has complained that "the FCC won't let me be" in his song Without Me.
Meanwhile, many radio stations refused to play records by the Dixie Chicks after their comment that they were "ashamed" President George W Bush came from their home state of Texas.
"It's very easy to censor the press, for instance, because newspapers need big offices, and they need reporters," said Andy Morgan, journalist and co-organiser of Mali's Festival in the Desert.
"Music can be produced outside a country, it can be smuggled in, it can be distributed, it can be copied ad infinitum.
"Even if the censor could gather up all the CDs and cassettes and burn them, the songs would still be in people's heads - which makes it so much more powerful."
Free Muse's Ms Corper is attempting to establish a global network of informants to help build up a complete picture of censorship around the world.
But she said it was prevalent in many African and some Asian countries, including Afghanistan, Malaysia, Burma, China, and Singapore
The most extreme example, however, is North Korea. There, the only music that is allowed is that which serves revolutionary ideas.
So "the only music considered of any value is that which glorifies the Great Leader and the revolutionary aspects of society", explained Simon Broughton, editor of magazine Songlines.
Even in North Korea, instruments are permitted - something not allowed under the Taleban in Afghanistan.
It was feared instruments would be a distraction from the teachings of the Koran, and they were seized by authorities and hung from the trees in effigy.
"Governments are scared of musicians," Maputo concluded.
"When [musicians] sing songs, they educate the people, to make people know what is really happening in this world, to make people know their mistakes."