The trial judge has ultimate control over the presentation of evidence at trial. Judges have the discretionary power to call witnesses on their own. The federal courts and most state courts have rules or codes of evidence. The balance of the states use the common law rules. In most circumstances, the failure to object to the presentation of evidence waives any possible grounds for objection to the presentation of that evidence. Failure to meet the burden of producing evidence results in a directed verdict in favor of the defendant.