`define('WP_DEBUG', 1);` works absolutely fine, but I am hacking an old theme and I would like to suppress 'deprecated' notices.

My understanding is that adding this;
`error_reporting( E_ERROR | E_NOTICE | E_PARSE )` should do the trick.

I have added it to wp-config.php and to header.php in my theme.

Unfortunately it has no effect. Is this something set at server level? 

`ini_set('display_errors', 1);` makes no difference.