使用Python的SpeechRecognition模块进行语音识别，使用Python的pyttsx3模块进行语音合成。在此基础上，可以使用Python的tkinter模块进行界面设计，实现语音转文字和文字转语音的功能。

以下是示例代码：

语音识别：

import speech_recognition as sr

r = sr.Recognizer()

with sr.Microphone() as source:
    print("请说话：")
    audio = r.listen(source)
    
try:
    text = r.recognize_google(audio, language='zh-CN')
    print("您说的话是：", text)
except sr.UnknownValueError:
    print("无法识别您说的话")
except sr.RequestError as e:
    print("请求出错：", e)

语音合成：

import pyttsx3

engine = pyttsx3.init()

text = "你好，欢迎使用语音合成功能"
engine.say(text)
engine.runAndWait()

界面设计：

import tkinter as tk
import speech_recognition as sr
import pyttsx3

def recognize_speech():
    r = sr.Recognizer()
    with sr.Microphone() as source:
        r.adjust_for_ambient_noise(source)
        print("请说话：")
        audio = r.listen(source)

    try:
        text = r.recognize_google(audio, language='zh-CN')
        print("您说的话是：", text)
        result_text.delete(1.0, tk.END)
        result_text.insert(tk.END, text)
    except sr.UnknownValueError:
        print("无法识别您说的话")
    except sr.RequestError as e:
        print("请求出错：", e)

def synthesize_speech():
    engine = pyttsx3.init()
    text = input_text.get(1.0, tk.END)
    engine.say(text)
    engine.runAndWait()

root = tk.Tk()
root.title("语音转文字和文字转语音")

input_label = tk.Label(root, text="请输入文字：")
input_label.grid(row=0, column=0)

input_text = tk.Text(root, width=40, height=5)
input_text.grid(row=1, column=0)

synthesize_button = tk.Button(root, text="文字转语音", command=synthesize_speech)
synthesize_button.grid(row=2, column=0)

result_label = tk.Label(root, text="语音转文字结果：")
result_label.grid(row=3, column=0)

result_text = tk.Text(root, width=40, height=5)
result_text.grid(row=4, column=0)

recognize_button = tk.Button(root, text="语音转文字", command=recognize_speech)
recognize_button.grid(row=5, column=0)

root.mainloop()

以上是一个简单的语音转文字和文字转语音的界面程序，可以根据实际需求进行修改和扩展。