IPhone : AVSpeechSynthesizer speaks, when runs again, takes 10 or so seconds before start

When I run this code, it runs fine, but when I run it again, it takes about 10 or so seconds before it runs and that too also gets cut off sometimes.

      NSString *string = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];
      AVSpeechUtterance *utterance = [[AVSpeechUtterance alloc] initWithString:string];
      utterance.rate = 0.1000;
      utterance.voice = [AVSpeechSynthesisVoice voiceWithLanguage:@"hi-IN"];

      AVSpeechSynthesizer *synthesizer = [[AVSpeechSynthesizer alloc] init];
      [synthesizer speakUtterance:utterance];
      //[synthesizer pauseSpeakingAtBoundary:AVSpeechBoundaryWord];