FSMN，一种能替代RNN的新结构？

FSMN

前言

FSMN全称：Feedforward Sequential Memory Networks，是国内知名的讯飞公司所提出，据笔者所知可能应用到了阿里的语音识别以及唤醒的，作为一种可以和RNN比较的网络，我觉得大家有必要的去学习以及了解一下

网络结构

在论文中的结构如图所示，其实FSMN是改进了DNN的算法，也就是在DNN网络中相应的某一层中加入了Memory block，这种结构分解起来就像是数字信号处理中的FIR。
其中当a为常数是sFSMN，当a为向量时，为vFSMN。
当没有时延时，公式可定义为：

h为输入特征，a为权重系数。
引入时延后，网络可改写为：

最后这一层的总的输出可以表示为：

模块搭建

语音数据输入，参数，以及模块的调用

length=50#帧长
input=39#MFCC特征维数
x = tf.placeholder(tf.float32,[None,length,input])#输入数据
FSMN1=memory_block(x,10,15,50,50)

搭建menory_block模块：

def memory_block(x,front,delay,input_size, output_size):
    #############pad 0
    x_pad_front=tf.pad(x,[[0,0],[front,0],[0,0]],"CONSTANT")
    x_pad_delay=tf.pad(x,[[0,0],[0,delay],[0,0]],"CONSTANT")
    h_memory=tf.random_normal([-1,1,39], 0)
    print(h_memory)
    print(x_pad_front)
    print(x_pad_delay)
    #############sum（a*h）+sum(c*h)
    for step in range(input_size):
        memory_block_front=x_pad_front[:,step:step+front,:]
        #print(memory_block_front)
        memory_block_delay=x_pad_front[:,step:step+delay,:]
        #print(memory_block_delay)
        FIR_1=tf.layers.conv1d(memory_block_front,39,1,strides=1, padding='same')
        FIR_1 = tf.reduce_sum(FIR_1, 1)  
        FIR_2=tf.layers.conv1d(memory_block_delay,39,1,strides=1, padding='same')
        FIR_2 = tf.reduce_sum(FIR_2, 1)  
        FIR = FIR_1+FIR_2
        FIR = tf.reshape(FIR,[-1,1,39])
        h_memory=tf.concat([h_memory,FIR],1)
    h_memory=h_memory[:,1:,:]    
    print(h_memory)
    ############ all
    h_memory=tf.layers.conv1d(h_memory,output_size,1,strides=1, padding='same')
    x=tf.layers.conv1d(x,output_size,1,strides=1, padding='same')
    h_next=h_memory+x
    h_next=tf.layers.conv1d(h_next,output_size,1,strides=1, padding='same')
    print(h_next)
    return h_next

代码解析：

memory_block(x,front,delay,input_size, output_size)

参数x代表输入语音，front代表前向多少帧的输入，delay代表后向时延，input_size输入语音的帧长，output_size输出语音特征大小。

   x_pad_front=tf.pad(x,[[0,0],[front,0],[0,0]],"CONSTANT")
    x_pad_delay=tf.pad(x,[[0,0],[0,delay],[0,0]],"CONSTANT")
    h_memory=tf.random_normal([-1,1,39], 0)
    print(h_memory)
    print(x_pad_front)
    print(x_pad_delay)
    #############sum（a*h）+sum(c*h)
    for step in range(input_size):
        memory_block_front=x_pad_front[:,step:step+front,:]
        #print(memory_block_front)
        memory_block_delay=x_pad_front[:,step:step+delay,:]
        #print(memory_block_delay)
        FIR_1=tf.layers.conv1d(memory_block_front,39,1,strides=1, padding='same')
        FIR_1 = tf.reduce_sum(FIR_1, 1)  
        FIR_2=tf.layers.conv1d(memory_block_delay,39,1,strides=1, padding='same')
        FIR_2 = tf.reduce_sum(FIR_2, 1)  
        FIR = FIR_1+FIR_2
        FIR = tf.reshape(FIR,[-1,1,39])
        h_memory=tf.concat([h_memory,FIR],1)
    h_memory=h_memory[:,1:,:]    
    print(h_memory)

x_pad_front和x_pad_delay分别代表前向补零和后向补零，对应第一个公式，sum（ah）+sum(ch)分别计算前向和后向
输出结果：

x_pad_front：Tensor("Pad_21:0", shape=(?, 60, 39), dtype=float32)
x_pad_delay：Tensor("Pad_22:0", shape=(?, 65, 39), dtype=float32)
前向得到的结果：Tensor("strided_slice_925:0", shape=(?, 10, 39), dtype=float32)
后向得到的结果：Tensor("strided_slice_926:0", shape=(?, 15, 39), dtype=float32)
 h_memory=Tensor("strided_slice_1157:0", shape=(?, 50, 39), dtype=float32)

    ############ all
    h_memory=tf.layers.conv1d(h_memory,output_size,1,strides=1, padding='same')
    x=tf.layers.conv1d(x,output_size,1,strides=1, padding='same')
    h_next=h_memory+x
    h_next=tf.layers.conv1d(h_next,output_size,1,strides=1, padding='same')
    print(h_next)
    return h_next

输出结果：

 h_next：Tensor("conv1d_1107/BiasAdd:0", shape=(?, 50, 50), dtype=float32)

最后all代表了公式2的计算

完整代码

import tensorflow as tf 


length=50#帧长
input=39#MFCC特征维数

def memory_block(x,front,delay,input_size, output_size):
    #############pad 0
    x_pad_front=tf.pad(x,[[0,0],[front,0],[0,0]],"CONSTANT")
    x_pad_delay=tf.pad(x,[[0,0],[0,delay],[0,0]],"CONSTANT")
    h_memory=tf.random_normal([-1,1,39], 0)
    print(h_memory)
    print(x_pad_front)
    print(x_pad_delay)
    #############sum（a*h）+sum(c*h)
    for step in range(input_size):
        memory_block_front=x_pad_front[:,step:step+front,:]
        #print(memory_block_front)
        memory_block_delay=x_pad_front[:,step:step+delay,:]
        #print(memory_block_delay)
        FIR_1=tf.layers.conv1d(memory_block_front,39,1,strides=1, padding='same')
        FIR_1 = tf.reduce_sum(FIR_1, 1)  
        FIR_2=tf.layers.conv1d(memory_block_delay,39,1,strides=1, padding='same')
        FIR_2 = tf.reduce_sum(FIR_2, 1)  
        FIR = FIR_1+FIR_2
        FIR = tf.reshape(FIR,[-1,1,39])
        h_memory=tf.concat([h_memory,FIR],1)
    h_memory=h_memory[:,1:,:]    
    print(h_memory)
    ############ all
    h_memory=tf.layers.conv1d(h_memory,output_size,1,strides=1, padding='same')
    x=tf.layers.conv1d(x,output_size,1,strides=1, padding='same')
    h_next=h_memory+x
    h_next=tf.layers.conv1d(h_next,output_size,1,strides=1, padding='same')
    print(h_next)
    return h_next

x = tf.placeholder(tf.float32,[None,length,input])#输入数据
FSMN1=memory_block(x,10,15,50,50)