Up Time Magazine- August/September 2008

there are certain sounds the MP3 vs. True Digital Wave Format human ear cannot hear, and MP3 was designed to Recording Mode WAV - 24 bit/48kHz WAV - 16 bit/44.1 kHz MP3 - 128kpbs/44.1 kHz others that it hears quite well. reduce the data file size Description The MP3 data format was created Provides professional recording quality for In the case of two simultaneof music that we want to to preserve the quality of WAV data digital audio by recording in 24 bit/48kHz. If while compressing the file size. Adous sounds, the MP3 comshare and transfer over you intend to burn a CD from the recording vantages are huge for sharing music then you would record at 16 bit/44.1kHz. This pression will keep the louder the Internet. For the most because wav files don’t need to be way the data transfer from PC to CD wouldn’t converted to MP3. Disadvantage if ones and lose the softer ones part, MP3 does a great require any conversion sound files are to be analyzed. that would otherwise be job of compressing digital Bits Recorded masked to the human ear. sound files while main~ 2,304,000 bps 1,411,200 bps 128,000 bps Per Second MP3 eliminates certain parts taining a reasonable reCapacity 5 minutes 5 minutes 128kbps: 5 minutes of the sound file it knows we production of the sound. About 100 MB About 50 MB About 5 MB can’t hear, and it does it in The majority of us are Figure 1 - Comparison Chart, MP3 vs. True Digital Wave Format such a way not to significantly more than happy to listen detract from the quality of the to MP3 reproductions on to use an ultrasound file that had not been sound as perceived by the listener. But what our MP3 enabled devices, but for hardcore manipulated by compression. if the listener wants to do more than just hi-fi audiophiles this format is completely listen? What if he wants to look as well? unacceptable. MP3 plays a limited role for How can you tell if an ultrasound file has ultrasound files as well. If you simply want Remember, one of the reasons we want to to share a sound file with a colleague or build been recorded in a true Digital Wave format or a compressed MP3 format? Since the record ultrasound files is for trending, analya library of sound files for training, then by MP3 format was designed to reduce file size sis, and diagnosis. An especially interesting all means, I fully endorse the MP3 compreswithout affecting the discernible quality to application is for finding faults in slow speed sion format. the human ear, it may be difficult to tell the bearings. The historical measurement probdifference by simply listening. But, comparlem for vibration analysis has been the slow Digital WAVE ing the size of the file to the length of the rotating speed – typically 14-16 rpm. To obsound sample should reveal the format, or tain good quality vibration data on machines Better than the MP3 format, the next option at least give an idea if a suitable sample rate rotating at such slow speeds means measureis the Waveform audio format or WAVE file. was used. The digital wave format creates ment configurations requiring 15-20 minutes There are two main features of the wave a file size around 50MB. A comparable MP3 per measurement. Since the bearing defects format that differentiate it from MP3. Firstly, format would produce a more manageable, we are watching for are rarely periodic, but wave files are not compressed, so their file albeit manipulated file size of about 5MB. rather impulsive or impacting in nature, they size is much larger. But putting up with the are more difficult to find with vibration; and bulkier file size is well worth it so as to avoid What effect does MP3 compression have much of the analysis done with vibration compression distortions that are probable on the original sound file? Compression tends to skip straight to the FFT which was in the MP3 format. Secondly, wave format never intended to be used for these kinds of files are created with a much higher sampling algorithms for text and images work by eliminating redundancy and replacing it with defects in the first place. rate, meaning more information is captured. links. Algorithms for sound compression use a process called Perceptual Noise Shaping. The time signals displayed in Figure 3 are Given this, how does one choose between The algorithm is based on the premise that from two identical music clips. The first is MP3 and Digital Wave format when recording an uncompressed digital wave ultrasound files? Well, having to format recording at CD quality choose between the two formats, How MP3 Files Work (44,100 kHz sample, 26 bit) and I would choose Wave, provided the second is the same file under that memory space on either my If there is a loud sound in one band, the influence of MP3 compression. compression algorithm can ignore all of recording device, or my PC, was the other bands. They look similar, but only if you not an issue. Secondly, I would don’t look too closely. ask one important question; why am I recording ultrasound files? Is They also sound similar, but only it because I want to build a library if you don’t listen too closely. I of sounds for training inspectors am worried by the amount of and to share amongst colleagues? data that has either been altered, If so, then the MP3 format will sufor is completely missing in the fice, and because of the smaller file MP3 representation. I would not size, sharing those files over the trust this time wave were it a Internet will be easier by conserve tim bearing diagnosis issue. Howing bandwidth and disk space. But ever, either of these files would if I plan to look at those signals in © 2001 HowStuffWorks be fine for building out a library a time or frequency domain softfor training purposes. ware then I would definitely prefer Figure 2 - Illustration of how MP3 compression works. fre que e nci s www.uptimemagazine.com 59 http://www.uptimemagazine.com

Table of Contents Feed for the Digital Edition of Up Time Magazine- August/September 2008

Up Time Magazine- August/September 2008 Contents Upfront Upclose Information Technology Lubrication Infrared Maintenance Management Motor Testing Precision Maintenance Reliability Ultrasound Vibration Upgrade

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