IN the first of this year's morning concerts on Saturday - a traditional element of the Perth Festival - the Edinburgh Quartet, playing a programme whose demands on both listeners and musicians made no concessions to the relatively early hour, gave one of the their finest performances since the group was effectively reconstituted under new leader, Jane Murdoch.

If there is a single overriding demand of a good performance of Schubert's late and deceptively straightforward A minor String Quartet, it is that the music should be played with restraint. And in an intepretation that was characterised by understatement the Edinburgh Quartet produced their best playing.

In every movement - from the first with its soft and undulating accompaniment underpinning the flowing violin melody, the second with its calm poise, the third with its dark, almost stealthy introspection, and the finale, to which the group brought a rare and unhurried sense of discretion - the Edinburgh Quartet played with a consistency of restraint that maximised the dramatic contrasts which explode out of the music from time to time.

In their more familiar style, strongly led by Jane Murdoch's big sound, her penchant for fast tempos, and her preferred tendency to ''walk on the wild side'', the group played Mozart's Dissonance Quartet, which had a bit of unwarranted tension, and Edward McGuire's fine Guest Quintet, whose sound world suggests a Celt teaming up with Bartok - witty, meaty, daring, wild, and rhapsodically lyrical with young Perth violist Alasdair Beatson in splendid form as the guest player.