MacResearch

In 'Showcase' reviews, the reviewer is the developer. No claim of objectivity is made, but it’s a chance for the developer to show off his/her app. Here, Faber Acoustical presents SignalScope Pro for the iPhone/ iPod Touch.

SignalScope Pro, which has been available for Mac OS X for over four years, has finally gone mobile. The new mobile version incorporates a significant portion of its desktop counterpart's functionality for real-time signal analysis and data acquisition.

SignalScope Pro 1.0 for iPhone OS devices is a real-time analysis toolset, suitable for use in areas such as acoustics, audio, electronics, and vibration. SignalScope Pro includes 3 tools for time or frequency domain signal analysis, as well as an internal signal generator for producing test signals. SignalScope Pro also turns your iPhone or iPod touch into a platform for data acquisition, storing acquired data in tab-delimited text files, MAT-files, or images for later retrieval from your device.

Input signals can be acquired from the built-in accelerometer, or from the current audio input path (the iPhone OS automatically selects the audio input path according to which external audio devices, if any, are connected to your device). Different engineering units, including Volts, Amps, pascals, g's, and ips (inches per second) can be assigned to input channels of the dock connector audio input or the headset input (not available on 1st generation iPod touch devices). Sensitivity calibration can also be performed for any audio input device or input channel.

Engineering units and sensitivity calibration allow SignalScope to be used for sound and vibration measurements in the lab, in the classroom, or in the field. By connecting a suitable power supply to a dock connector input device (or possibly to the headset input), a vast array of accelerometers and precision microphones can be connected to your iPhone or iPod touch.

Like with SignalScope for iPhone, SignalScope Pro allows you to "touch" your data with hardware-accelerated (OpenGL ES) multi-touch analyzer displays. You can zoom in on the narrowband spectrum and oscilloscope displays with two-finger pinching gestures and pan the zoomed display by dragging two fingers. You can place or move a data cursor by tapping or dragging a single finger. A double-tap resets the display to its un-zoomed state and a second double tap turns off the cursor. Vertical display scaling can be automatically or manually adjusted. Manual adjustment can be made when auto-scaling is turned off. To adjust the vertical offset of the display, just drag your finger up or down within the vertical axis label region of the display. Two-finger pinching gestures within the same region will increase or decrease the vertical scale. Adjusting the time scale can be accomplished in a similar manner within the horizontal axis label region of the oscilloscope display. In the oscilloscope, the time offset can also be reset by double tapping within this same region.

• Features:
  • Analyze signals coming from the iPhone OS device's current audio input device or from the built-in accelerometer
  • Audio input is sampled at 48 kHz, built-in accelerometer data is sampled at 100 Hz
  • Assign engineering units to your input signals and calibrate external transducers for accurate measurements
  • Save acquired time or frequency data to tab-delimited text files or MAT-files
  • Retrieve your data files from your device through a web browser on your Mac or PC
  • Captured data files reduce note-taking for researchers by including valuable information, such as
    • Name and version of the app
    • Date and time the data was saved
    • Type of iPhone OS device (iPhone or iPod touch) and its name
    • Units used for the measurement
    • Input device and/or channel sensitivity
    • Input sample rate
  • Save high-resolution analyzer display images to the iPhone OS device's built-in photo album
  • Pinpoint individual sample values or frequencies with a cursor
  • Zoom in or out on spectrum and waveform displays with two-finger expand/pinch gestures, even while the analyzer is running (FFT analyzer and oscilloscope)
  • Pan vertically or horizontally in zoomed displays with two-finger scrolling (FFT analyzer and oscilloscope)
• Tools:
  • FFT Analyzer
    • FFT lengths range from 100 to 9600 lines (50 to 4800 visible spectral lines)
    • Input data can be windowed with one of the following data window types:
      • Uniform (Rect)
      • Bartlett
      • Blackman
      • Flat Top
      • Hamming
      • Hann
      • Rife-Vincent 2
    • Lin, log, and dB magnitude scales
    • Lin and log frequency scales
    • Linear (stable) and exponential averaging with an arbitrary number of averages
    • Peak hold over a specified number of spectra
    • Peak tracking cursor
    • Harmonic cursors
    • Display frequency in Hz or cpm
  • Fractional Octave Band Analyzer
    • Whole and 1/3-octave RTA (based on digital Butterworth bandpass filters, as recommended by ANSI--not FFT)
    • Equivalent and time-weighted exponential average levels
    • Fast, Slow, and Impulse exponential time weighting
    • Flat, A, and C frequency weighting
    • Max and peak levels, as well as elapsed time also captured
    • Optional secondary level display
    • Display frequency in Hz or cpm
  • Oscilloscope
    • Time scales from 0.1 to 500 ms per division
    • Auto, normal, and single-shot triggering
    • Trigger slope and threshold options
  • Stereo Signal Generator
    • Random and periodic pseudorandom noise (period defined by FFT length)
    • White and pink noise weighting
    • Lin and log frequency sweeps (duration defined by FFT length)
    • Tone generator
    • Invert the polarity of either or both output channels
    • White pseudorandom noise and linear sweeps can be used for quick frequency response measurements with the FFT analyzer
    • Pink pseudorandom noise and log sweeps can be used for quick frequency response measurements with the octave analyzer

NOTE: The frequency response of the iPhone's built-in and headset microphones is quite flat. However, the built-in microphone of the original iPhone seems to be routed through a codec, which limits the sample rate to 8 kHz and significantly affects the frequency response. The iPhone 3G rolls off the built-in mic and headset input signals below 100 Hz.

NOTE: iPod touch devices require additional external hardware to get audio signals into SignalScope.

Those interested in learning more about SignalScope Pro can visit the following links:

• SignalScope Pro web page
• SignalScope Pro forum
• SignalScope Pro help docs
• SignalScope Pro in the App Store

Feedback from current and potential users would also be appreciated: Submit Feedback