System: As an API testing assistant, analyze API specifications and previous test results to generate new, unused parameters. Avoid using any parameters from the previous attempts. Return only the parameter dictionary.
User: API Specification:
URL: https://api.songzixian.com/api/text-to-speech
Method: POST
Required Parameters: [{'name': 'text', 'type': 'string', 'description': '要转换的文本内容', 'default': ''}, {'name': 'voice', 'type': 'string', 'description': '选择语音角色，例如：xiaoyun、xiaoming等', 'default': 'xiaoyun'}, {'name': 'speed', 'type': 'int', 'description': '语音播放速度，取值范围1-10，默认为5', 'default': 5}, {'name': 'volume', 'type': 'int', 'description': '语音播放音量，取值范围1-10，默认为5', 'default': 5}, {'name': 'pitch', 'type': 'int', 'description': '语音播放音调，取值范围1-10，默认为5', 'default': 5}, {'name': 'format', 'type': 'string', 'description': '输出文件格式，如mp3、wav等，默认为mp3', 'default': 'mp3'}, {'name': 'appid', 'type': 'string', 'description': '应用ID，用于验证调用者身份', 'default': ''}, {'name': 'sign', 'type': 'string', 'description': '签名，用于验证请求的合法性', 'default': ''}]
Optional Parameters: []
Previous attempts: Initial Attempt 1:
Parameters: {'text': 'Hello, how are you?', 'voice': 'xiaoming', 'speed': 7, 'volume': 6, 'pitch': 4, 'format': 'wav', 'appid': 'your_app_id', 'sign': 'your_signature'}
Result: Success
Analysis: Success - parameters worked well

Initial Attempt 2:
Parameters: {'text': 'The quick brown fox jumps over the lazy dog.', 'voice': 'xiaoyun', 'speed': 3, 'volume': 8, 'pitch': 6, 'format': 'mp3', 'appid': 'new_app_id', 'sign': 'new_signature'}
Result: Success
Analysis: Success - parameters worked well

Recent Attempt 3:
Parameters: {'text': 'The sun is shining brightly today.', 'voice': 'xiaoming', 'speed': 4, 'volume': 9, 'pitch': 2, 'format': 'wav', 'appid': 'unique_app_id', 'sign': 'unique_signature'}
Result: Success
Analysis: Success - parameters worked well

Recent Attempt 4:
Parameters: {'text': 'The future of technology is bright.', 'voice': 'xiaoyun', 'speed': 6, 'volume': 5, 'pitch': 7, 'format': 'mp3', 'appid': 'new_unique_app_id', 'sign': 'new_unique_signature'}
Result: Success
Analysis: Success - parameters worked well

Recent Attempt 5:
Parameters: {'text': 'Exploring the wonders of the universe.', 'voice': 'xiaoming', 'speed': 8, 'volume': 3, 'pitch': 5, 'format': 'mp3', 'appid': 'new_exploration_app_id', 'sign': 'new_exploration_signature'}
Result: Success
Analysis: Success - parameters worked well

Already used parameters: - {'appid': 'new_app_id', 'format': 'mp3', 'pitch': '6', 'sign': 'new_signature', 'speed': '3', 'text': 'The quick brown fox jumps over the lazy dog.', 'voice': 'xiaoyun', 'volume': '8'}
- {'appid': 'unique_app_id', 'format': 'wav', 'pitch': '2', 'sign': 'unique_signature', 'speed': '4', 'text': 'The sun is shining brightly today.', 'voice': 'xiaoming', 'volume': '9'}
- {'appid': 'another_app_id', 'format': 'mp3', 'pitch': '8', 'sign': 'another_signature', 'speed': '5', 'text': 'Artificial intelligence is transforming the world.', 'voice': 'xiaoyun', 'volume': '7'}
- {'appid': 'new_unique_app_id', 'format': 'mp3', 'pitch': '7', 'sign': 'new_unique_signature', 'speed': '6', 'text': 'The future of technology is bright.', 'voice': 'xiaoyun', 'volume': '5'}
- {'appid': 'your_app_id', 'format': 'wav', 'pitch': '4', 'sign': 'your_signature', 'speed': '7', 'text': 'Hello, how are you?', 'voice': 'xiaoming', 'volume': '6'}
- {'appid': 'new_exploration_app_id', 'format': 'mp3', 'pitch': '5', 'sign': 'new_exploration_signature', 'speed': '8', 'text': 'Exploring the wonders of the universe.', 'voice': 'xiaoming', 'volume': '3'}

Rules:
1. If required_parameters is empty and you choose not to use optional parameters, return empty dict.
2. If using optional parameters, only use parameters exactly as defined in optional_parameters.
3. Do not create new parameters that are not in the specification.

Generate valid parameters:
Assistant: