ধ্বনিবিজ্ঞান
ধ্বনিবিজ্ঞান () মানুষের উচ্চারিত ধ্বনিসমূহের বিশ্লেষণ। ধ্বনিতত্ত্বের সাথে ধ্বনিবিজ্ঞানের পার্থক্য হল ভাষাবিজ্ঞানের এই শাখায় ধ্বনির ভৌত তরঙ্গধর্মী প্রকৃতি, এর উৎপাদন, শ্রবণ ও অনুধাবন নিয়ে গবেষণা করা হয়, কিন্তু ধ্বনিতত্ত্বের মত বিভিন্ন ধ্বনি-একক, তাদের শনাক্তকারী বৈশিষ্ট্য ও ধ্বনি-ব্যবস্থা নিয়ে গবেষণা করা হয় না। 
ধ্বনিতত্ত্ব (উচ্চারণ / /fəˈnɛtɪks / গ্রিক φωνή থেকে:, ফোন, 'শব্দ, ধ্বনি ') ভাষাতত্ত্বের একটি শাখা যার মধ্যে রয়েছে মানুষের কথার অন্তর্গত শব্দের গবেষণা, অথবা ভাষার ক্ষেত্রে চিহ্নের ব্যবহার-বা চিহ্নের সমতুল্য দিক। 
ধ্বনিবিজ্ঞানের তিনটি প্রধান শাখা:
জ্যোতির্বিজ্ঞান
তবে জ্যোতির্বিজ্ঞানের সর্বপ্রধান সীমাবদ্ধতা বা অন্য যাই বলা হোক না কেন তা হল এটি এখনও একটি খাঁটি পর্যবেক্ষণমূলক বিজ্ঞান। অনেক দূরবর্তী বস্তুসমূহ নিয়ে গবেষণা করতে হয় বিধায় এতে পরীক্ষণের সুযোগ খুবই সীমিত। তাছাড়া যে বস্তুসমূহ নিয়ে পরীক্ষা নিরীক্ষা করতে হয় সেগুলোর তাপমাত্রা, চাপ বা রাসায়নিক গঠন সম্পর্কে কোনও তথ্যকেন্দ্রিক নিয়ন্ত্রণ থাকা সম্ভব নয়। তবে বর্তমান যুগে এই বিজ্ঞানের বেশ কয়েকটি উল্লেখযোগ্য পরীক্ষণ চালনা সম্ভব হয়েছে; যেমন: ভূপৃষ্ঠে পতিত উল্কাপিণ্ড, পাথর বা চাঁদ থেকে নিয়ে আসা মাটি নিয়ে বিস্তর গবেষণা সম্ভব হয়েছে। এর সাথে পৃথিবীর বায়ুমণ্ডলের স্ট্র্যাটোস্ফিয়ার স্তরে প্রাপ্ত ধূলিকণা নিয়ে গবেষণাও এর অন্তর্ভুক্ত। এভাবে জ্যোতির্বিদ্যা পর্যবেক্ষণ ক্ষেত্রেও প্রসিদ্ধি লাভ করছে। ভবিষ্যতে হয়তোবা ধূমকেতুর ধূলিকণা বা মঙ্গল গ্রহের মাটি নিয়ে মহাশূন্যযানে বসেই গবেষণা করা যাবে। তবে এসব গবেষণার বেশীর ভাগই পৃথিবীকেন্দ্রিক। পর্যবেক্ষণকাজে বিজ্ঞানের অন্য শাখাসমূহের সাহায্য এখানে মুখ্য। সহযোগী শাখাসমূহের মধ্যে আছে পদার্থবিজ্ঞান, রসায়ন, অণুজীববিজ্ঞান, প্রত্নতত্ত্ব ইত্যাদি।
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