Physics 4060, Acoustics Laboratory

As another approach to sound analysis, the three pre-recorded tones from the previous will be analyzed using the MacScope digital sampling interface and the accompanying Fast Fourier Transform analysis software. The MacScope will be used at its fastest rate, a 20ms sampling time which corresponds to 50 kHz sampling rate. For comparison, the A/D samplers for the production of audio compact discs usually operate at a 44 kHz rate.

作为另一种声音分析方法，先前的三个预录制音调将使用MacScope数字采样接口和配套的快速傅里叶变换分析软件进行分析。MacScope将以最快的速度运行，即20 m s的采样时间，对应50 kHz的采样率。相比之下，用于生产音频光盘的A/D采样器通常以44 kHz的速率运行。

Play the tape of your sounds through the Peavy sound board and connect the Monitor output to the oscilloscope. Adjust the Monitor level (blue knob on right of console) so that the peak-to-peak voltage is about 2 volts. Branch the monitor output so that you can also connect it to input #3 of the Macscope.

将你的声音磁带通过Peavy声音板播放，并将Monitor输出连接到示波器。调整Monitor电平（ console右侧的蓝色旋钮）使峰峰值电压约为2伏特。将Monitor输出分支，以便也可以将其连接到Macscope的输入#3。

If the Macscope software is not running, start it by double-clicking on the Macscope icon on the screen. It takes a minute or so for the software to load. Adjust the Amp to 2 by using the mouse and the pull-down menu at the top of the screen. Examine the Input menu and make sure #3 is selected. The Time menu should be set to Trigger and Automatic , which will set it to the maximum time resolution of 20 _s. In this configuration, the analog-to-digital converter will collect about 70 milliseconds of data, enough for several periods of your sound waveform.

如果Macscope软件没有运行，请双击屏幕上的Macscope图标启动它。软件加载大约需要一分钟时间。使用鼠标和屏幕顶部的下拉菜单，将Amp调整为2。检查Input菜单，确保选中#3。Time菜单应设置为Trigger和Automatic，这将设置最大时间分辨率为20毫秒。在这种配置下，模拟-数字转换器将采集约70毫秒的数据，足以记录几个声音波形周期。

To collect data, play the tape and listen for the desired sound. When it starts, click the Stop/Go button on the screen with the mouse. It will display "GOING" below the button and collect data until the data buffer is full. When it is finished, it will display "STOPPED". After examining the display to make sure than you have captured a sample, save the data file on an external floppy disc with a name which indicates the person and the sound, like JimFlute or JohnAh.

为了收集数据，请播放磁带并聆听所需的声音。当开始播放时，用鼠标点击屏幕上的停止/开始按钮。它会在按钮下方显示“GOING”，并开始收集数据，直到数据缓冲区填满。当收集完毕时，它会显示“STOPPED”。在检查显示以确保已捕获一个样本后，将数据文件保存到外部软盘上，文件名应表明人物和声音，例如JimFlute或JohnAh。

For each of your three sounds, the assignment involves displaying the waveform and doing an FFT analysis as illustrated in Figure 1 below.

对于你的三个声音，任务包括显示波形并进行如图1所示的FFT分析。

The controls you have at your disposal to do this analysis are illustrated in Figure 2. After examining the data file, adjust the controls so that one waveform fills at least two-thirds of the screen horizontally so that you have sufficient resolution to accurately select one period of the sound. Carefully position the cursor at one recognizable peak and hold down the mouse button and drag the corner of the dashed rectangle which appears to the corresponding peak one period later. Before releasing the mouse button at the next peak, note the measured frequency which is displayed in the information box and make a note of it in your data. When you release the mouse, the period you have chosen will be displayed with a bold line. Now select FFT from the Analyze menu and expand the resulting bar graph as much as possible horizontally using the Expand button. At this point you should save the image of the waveform and FFT analysis you have done for your report. This can be done by holding down the Command and Shift keys simultaneously and pressing 3. This stores the screen as a "paint" document named Picture 0, Picture 1, Picture 2, etc. It will be a good idea to bring this saved file up on the screen using Deskpaint under the Apple Menu or Microsoft Word so that you can save it with a more descriptive title. You need to produce a print of this file for your report.

你可用于进行此分析的控件如图2所示。在检查数据文件后，调整控件使一个波形在水平方向至少覆盖屏幕的三分之二，以便你有足够的分辨率来准确地选择一个声波周期。将光标仔细地定位在一个明显峰值处，按住鼠标按钮并拖动出现的虚线矩形的角落，将其移动到对应峰值一个周期之后的位置。在释放鼠标按钮到下一个峰值之前，注意信息框中显示的测量频率，并将其记录在你的数据中。当你释放鼠标时，你所选择的周期将用粗线显示。现在从分析菜单中选择FFT，并使用展开按钮尽可能地将结果的条形图水平展开。此时你应该将你所进行的波形和FFT分析的图像保存下来用于你的报告。这可以通过同时按住Command和Shift键并按下3来完成。这会将屏幕保存为一个名为Picture 0、Picture 1、Picture 2等的“画图”文档。使用Deskpaint在Apple菜单下或Microsoft Word中将此保存的文件调出到屏幕上，以便用更具有描述性的标题保存它。你需要为你的报告打印这个文件。

图1：'Ah'元音声音的波形显示和FFT分析

对于你的三个声音样本，其处理步骤如下：

1. For five periods in succession, perform the FFT and record the relative amplitudes of the first few harmonics - i.e., those which are greater than a few percent of the fundamental. Calculate average amplitudes and standard deviations for these harmonics and report these averages as your spectrum for this sound.

1. 连续进行五次FFT分析，并记录前几个谐波的相对振幅——即那些振幅大于基频几个百分点的谐波。计算这些谐波的平均振幅和标准差，并将这些平均值作为该声音的频谱报告。

2. Record the amplitudes and phases of the significant harmonics of one period and then resynthesize the wave with a 50 point plot using the Excel spreadsheet on the lab Macintosh (or a spreadsheet of your own choice).

记录一个周期内显著谐波的振幅和相位，然后使用实验室Macintosh上的Excel表格（或你选择的其他表格）绘制50点的重合成波形。

All of the components of your report can be put together with Microsoft Word and printed as a single document if you care to. Otherwise you can print out the various components and put them together in your report.

Sound Analysis II

MacScope Fast Fourier Transform

Physics 4060: Acoustics Laboratory

Physics 4060 Laboratory