<?php

craft()->on('assets.beforeSaveAsset', function(Event $event) {
    if ($event->params['isNewAsset']) {
        $asset = $event->params['asset'];
        $source = $asset->getSource();

        if (in_array($source->handle, ['myAssetSource'])) {
            $asset->getContent()->title = 'myAssetTitle';
        }
    }
});