I heard them in a narrow street in north Tehran, not one of the rich villa-lined avenues we associate with the Iranian middle classes but a tired thoroughfare of overheated plane trees and shabby, two-storey offices in grey concrete.

The sound was of a scratched record, a 78-rpm rather than a 33-and-a-third, and when I turned to my driver, he assured me there must be some morning party up the road with an old gramophone. But I used to play the violin, and I didn't believe him. And sure enough, down the street came the troubadours.

Yes, real live troubadours in the real live Islamic Republic, two of them, hacking at a violin and beating on a “zarb” drum, the work of the classical Persian musicians, a combination — for a westerner — of gypsy and nursery melodies, a sudden revelation of 14th and 15th century music in a regime which aspires to the purity of the 8th. Habibullah Zendegani introduced himself very quietly and said he was only 26 but had been playing for 15 years.

Beside him, Ramezan Souratipour banged away happily on the drum under his arm, one of a thousand little drummers in Iran — he is 32, but a diminutive figure — whose fingers dab three to a second to Zandegani's violin.

But I am old enough to remember Ruhollah Khomeini banning Mozart and Haydn. So how do the Revolutionary Guards, praetorians of the Ayatollah's spirituality in President Ahmedinejad's oh-so-chaste republic, react to these ghosts of culture past?

“I play music to earn money,” Zandegani replies, a little shiftily I think. “We earn maybe $40 or $50 a day.”

In theory, all music must pass Iran's censorship authorities; a female singer, for example, is not allowed to sing solo lest her lone voice be too arousing for male listeners.

But music and Islam have a dodgy relationship. In Saudi Universities the most sanctimonious of students have assaulted music enthusiasts; when a professor at King Saud University, Hamzah Muzeini, condemned this brutality in the daily Al-Watan newspaper, he was convicted by a Sharia court — a ruling later overturned by King Abdullah. Yet according to journalist Rabah al-Quwai'i, some sheikhs encourage youths to burn instruments and books in public.

In my own country of choice, Lebanon, the Ministry of Defence monitors music, according to musician Mohamed Hamza. In November, 1999, Marcel Khalife was charged with blasphemy before the Beirut courts, an outrageous infringement of cultural liberty supported by the Sunni Grand Mufti, Mohamed Kabbani.

Khalife had set a verse by Palestinian poet Mahmoud Darwish to music in his album Arabic Coffeepot, but Darwish's poem contained lines from the Koran and protesters argued that Khalife had defiled the Koran by singing it as part of a commercial song.

Shiite clerics — to their great credit — defended the song-writer. He was acquitted, the Beirut judge adding that Khalife had “chanted the poem in gravity and composure that reveal a deep perception of the humanism expressed in the poem ornamented with the holy phrase.” Phew.

On Al-Jazeera television, Sheikh Yusef al-Qaradawi claims there's nothing forbidden about music unless it is slanderous, sexually exciting or — and here's the rub — if it's listened to with over-enthusiasm (Islam supposedly being against all things in excess).

Sufis have suggested that uneducated listeners may be stirred to sexual desire while experienced practitioners are moved by music to do God's will. The old, I suppose, know how to control themselves when they hear Mozart's “Jupiter” symphony.

I guess it's really all to do with that most jealously guarded commodity, the human soul, over which music exerts such passion. While the passion of humans should be directed towards God, music, it seems, is a diversion, even worse a perversion, the path to alcohol, adultery, murder.