Recording Ultrasound

1
Recording Ultrasound

• Choosing the Right Recording Method for
• AVM Ultranalysis
• Author Allan Rienstra
• Contributions by Thomas J. Murphy C.Eng.
• SDT North America

2
Why Record Ultrasound?

• Why Record Ultrasound
• comparison
• trending
• training
• consulting
• diagnosis
• analysis
• second opinion

3
Options for Recording Ultrasound

• Analogue to magnetic tape
• Digital
• MP3
• Wave
• Vibration data collector

4
Magnetic Tape

• Too many noise sources in the recording process
• Speed and instability (wow and flutter)
• Capstan noise (rumble)
• Tape hiss (would compete with ultrasound
  frequencies)

5
MP3

• MPEG-1 Audio Layer 3
• MP3 is the abbreviation
• Designed to reduce data file size
• While maintaining reasonable reproduction of
  sound
• Not considered hi-fi by audiophiles

6
Wave

• Waveform audio format
• This is an uncompressed format
• Larger file sizes
• Less likely to produce compression distortions
• The better method for recording U/S signals

7
Summary Comparison
Record Mode Description Capacity
WAV 24bit/48kHz 16bit/44.1kHz Provides professional recording quality for digital audio by recording in 24 bit/48kHz. If you intend to burn a CD from the recording then you would record at 16 bit/44.1kHz. This way the data transfer from PC to CD wouldnt require any conversion 24 bit 5 minutes About 100 MB 16 bit 5 minutes About 50 MB
16 bit waveform 44,100 samples/second x 16 bits/sample x 2 channels 1,411,200 bits per second 16 bit waveform 44,100 samples/second x 16 bits/sample x 2 channels 1,411,200 bits per second 16 bit waveform 44,100 samples/second x 16 bits/sample x 2 channels 1,411,200 bits per second
MP3 128kbps/44.1kHz The MP3 data format was created to preserve the quality of WAV data while compressing the file size. Advantages are huge for sharing music because wav files dont need to be converted to MP3. Disadvantage if sound files are to be analyzed. 128kbps 5 minutes About 5 MB
MP3 compressed format 128,000 bits per second MP3 compressed format 128,000 bits per second MP3 compressed format 128,000 bits per second
8
MP3 Compression

• Perceptual Noise Shaping
• Compression algorithm based on sounds that are
  perceived (or not) by the human ear

9
Comparing MP3 and Wave

• Two identical music clips
• The top time signal is16 bit wave recording
• Bottom time signal is MP3 128kbps compressed
  recording

10
How to Record

• Connect to headphone output of Ultrasonic
  Detector
• Adjust amplification of detector
• Adjust recording level of recording device
• Turn off AGC if possible
• Record signal
• Name sound file for later reference

11
Setting the input level

• Auto Gain Control
• Manual Gain Control
• Clipping

12
Vibration data collector

• This is a special case
• Should always produce a good quality time signal
  though clipping is still possible
• Easily transferred to software for analysis and
  comparison
• Will normally only acquire a relatively short
  amount of data

13
Conclusions

• Choose your reason for recording ultrasounds
• Choose your recording device according to your
  goals
• Follow the recommended procedure for capturing
  the sound files
• www.sdtnorthamerica.com
• 1-800-667-5325
• 1-905-377-1313