SignalScope Pro 3.0 for iOS 7

In the new version 3, SignalScope Pro’s appearance has been completely revamped for iOS 7. SignalScope Pro supports both iOS 6 and iOS 7, but looks largely the same on iOS 6 as the previous version.

Also new in version 3:

– Audio data handling is more efficient.

– Image overlays created in the Level Meter tool now use the full resolution of the original image (whether the image comes from the photo library or straight from the camera).

– For devices that support input gain adjustment on the built-in or headset microphone, the input gain is stored with data exported from the FFT, Octave, or Oscope tools.

– When entering a preferred sample rate, “48k” can be entered in the text box, as an alternative to typing out “48000.”

– Default input sensitivities have been updated, based on measurements of the iPhone 5S and 5C microphones and headset inputs.

– Cursor info text now uses a larger font.


SignalScope Pro Screenshot iPhone 1 SignalScope Pro Screenshot iPhone 4 SignalScope Pro Screenshot iPhone 5

SignalScope Pro Screenshot iPhone 2 SignalScope Pro Screenshot iPhone 3


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SignalScope, SoundMeter, and dB have also received similar updates for iOS 7.

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Octave Analyzer tool for iOS


The Octave Analyzer tool for iOS performs real-time spectral analysis in whole or 1/3-octave frequency bands.

The Octave Analyzer tool is built into SignalScope Pro. It is also available in SignalScope and SoundMeter via in app purchase.

The Octave Analyzer can analyze up to two audio input channels simultaneously (this requires a two-channel input device).

The Octave Analyzer can be configured with several options that are common to overall sound level meters. These options include time weighted exponential average levels with fast, slow, and impulse response times as well as the equivalent level, which expresses an average signal level over the total measurement time. Flat, A, and C frequency weighting are also available.

The Octave frequency spectrum appears within a bar graph which can be adjusted in its vertical scale either manually or automatically. In addition to current levels within each frequency band, maximum or peak levels may also be displayed, depending on which level type is selected. A data cursor allows specific levels at specific frequencies to be identified. The entire graph can be saved either as an image in the iOS photo library, or as a high resolution PDF file within the app.

Additionally, in SignalScope Pro, Octave analyzer data may be exported to CSV, MAT, or tab-delimited text files. Data export is also possible in SignalScope and SoundMeter with the optional Data Acquisition Upgrade available via In-app Purchase.


SignalScope Pro



SignalScope and IOScope support sample rates up to 192 kHz

Current versions of SignalScope (3.6.2), SignalScope Pro (2.6.2), and IOScope (2.5) include advanced audio configuration options that support user selection of the audio sample rate. Using built-in iPhone and iPad audio hardware, this typically means that sample rates as low as 8 kHz can be selected. Since the iPad additionally supports external USB audio devices, via the iPad Camera Connection Kit or the Lightning to USB adapter, sample rates as high as 192 kHz can be made available with the right hardware. Which sample rates can be selected depends on values supported by the connected audio hardware.

Typical sample rates for the built-in microphone or headset input of current iOS devices include:

  • 8 kHz
  • 11025 Hz
  • 12 kHz
  • 16 kHz
  • 22.05 kHz
  • 24 kHz
  • 32 kHz
  • 44.1 kHz
  • 48 kHz

It is possible to sample audio data at up to 192 kHz, with USB devices that support it, on iPad. One such device is the Echo 2 from Echo Digital Audio, which supports sample rates of:

  • 44.1 kHz
  • 48 kHz
  • 88.2 kHz
  • 96 kHz
  • 176.4 kHz
  • 192 kHz

SignalScope, SignalScope Pro, and IOScope are all available for download on the App Store.

Download SignalScope

Download SignalScope Pro

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The Echo 2 is available from B&H Photo Video and from Amazon.

SignalScope Pro 192 kHz Sampling

RoomScope and IOScope measure longer IRs and use 64-bit FFTs

RoomScope 1.2 and IOScope 2.3 arrived in the iOS App Store this week. Both apps now support impulse response measurements up to 16 seconds long and use double precision (64-bit) FFTs in their measurements. The maximum measurement length is dependent on the amount of memory available on the device, so 16-second measurements are currently only supported on the iPhone 5, iPad 3, and iPad 4. The previous generation of devices, including the iPod touch 5, supports 10-second measurements, and older devices are still limited to measurement durations of 5 seconds or less.

RoomScope 1.2 also offers the following additions:

  • Center time has been added to the list of calculated acoustic parameters.
  • All parameters are now calculated in low, mid, and high frequency bands, as defined by the ISO 3382 standard.
  • The calculation of the clarity and definition parameters (C and D) compensates for the delay of the whole and 1/3-octave band filters, as described in ISO 3382.
  • Raw IR data can now be excluded or included in CSV, MAT, and TXT file data exports.

RoomScope turns your iPad, iPhone, or iPod touch into a room acoustics measurement and analysis tool. With RoomScope, you can measure a room impulse response and then calculate reverberation time, early decay time, center time, clarity, and definition, as defined in the ISO 3382 standard. RoomScope also allows you to adjust the Schroeder decay curve integration limits with the touch of your finger and plot the calculated room parameters versus whole or 1/3-octave band center frequency.



Download RoomScope 1.2

IOScope brings true dual-channel transfer function and impulse response analysis to iOS. With IOScope, measure loudspeaker impedance, frequency response, and sensitivity. Measure a room impulse response. Tune a large sound reinforcement system, time-align a set of surround sound speakers, or optimize your home stereo. Determine the actual cutoff frequencies of your latest speaker crossover circuit, or teach your students the fundamentals of Fourier analysis of dynamic systems.

Measure frequency response magnitude and phase, coherence, and group delay. Time domain functions enable you to measure impulse response and auto/cross-correlation. IOScope includes a built-in signal generator for producing suitable excitation signals to analyze your system or device under test (DUT). See for a video demo of loudspeaker impedance measurement.


Download IOScope 2.3


Frequency Response Measurement with SignalScope Pro 3 (Mac)

Measuring the Frequency Response of Your Audio Device

Although SignalScope Pro does not include the Dual FFT Analyzer tool, found in Electroacoustics Toolbox, it is still equipped to perform basic frequency response measurements. This tutorial focuses on using SignalScope Pro’s FFT Analyzer and Signal Generator tools to measure the frequency response of the audio device that you use as an analog interface to measure other systems and devices. If you want to measure the frequency response of a listening room for example, that measurement will be affected by the quality of the audio interface that you are using to make the measurement. Therefore, it is important to know how your measurements will be influenced by your audio interface.

When measuring the properties of some device, like its frequency response, that device is commonly referred to as the “device under test” or DUT. In this case, the DUT is actually the audio device that would normally be used as part of the complete measurement system you use to measure other DUT’s.

Measuring Your Audio Device

  1. Connect your device to your Mac (if necessary, you may want to consult your device’s user guide or owner’s manual).
  2. Using a patch cable that is appropriate for the device you are using, connect one or more outputs of the device to one or more inputs of the same device. Figure 1 demonstrates the connections using an Echo AudioFire4 FireWire interface. It is important to keep in mind that what will be measured in this tutorial is actually the combined frequency response of the input channel, the output channel, and even the patch cable between them.
    Figure 1: 1/4″ plug patch cable


  3. Launch SignalScope Pro, if necessary.
  4. Create a new project, if one was not created automatically when the program launched.
  5. Click the Device IO button in the project window’s toolbar to open up the Device IO Setup window.
  6. In the Device IO Setup window, click on the name of the device you would like to measure in the Available Devices list. This will display the device’s properties in the lower portion of the window.
  7. Make sure the nominal sample rate is set high enough to capture the desired frequency range. For this tutorial, select 44100 or 48000 Hz.
  8. Select your device from both the Input Device and Output Device popup menus in the project window. If your device does not have both input and output channels, you will need to select one that does, or use the Aggregate Device Editor in the Audio MIDI Setup application to create one. (Audio MIDI Setup is included with Mac OS X in the /Applications/Utilities/ folder.)
  9. Create a new FFT Analyzer tool. This can be accomplished by clicking the “+” button in the FFT Analyzer row of the project toolbox, selecting FFT Analyzer from the Tools menu in the project window’s toolbar, or by selecting New FFT Analyzer from the Tools menu.
  10. Select the Live Inputs tab in the controls drawer at the bottom of the Dual FFT Analyzer window.
  11. In the analyzer table below the Input Device label, the first row will already be pre-filled for Analyzer 1. For Analyzer 1, change the channel in the Input column to match the physical input channel connected in step 2.
    • The name of each analyzer can be edited by double clicking on it within the Channel column of the table, either in the Display tab or in the Live Inputs tab.
  12. If you connected multiple physical input/output channel pairs in step 2, click the “+” button above the analyzer table to add an additional analyzer for each additional channel pair and configure the input channels as in the previous step.
  13. In the FFT tab of the FFT Analyzer’s controls drawer, set the number of spectral lines to a value that will provide the frequency resolution you need. For the purposes of this tutorial, select 4410 spectral lines if your DUT’s sample rate is 44100 Hz or 4800 lines if your sample rate is 48000 Hz.
    • The frequency resolution of your measurement can be determined by the selected frequency span (which is dependent on the sample rate) and the number of spectral lines. You can calculate the frequency resolution by dividing the frequency span by the number of lines (if guardbanding is turned off). For example, if the selected frequency span is 24000 Hz, and the number of lines is 4800, the frequency resolution will be 24000/4800 = 5 Hz. You can also view the current frequency resolution of the analyzer inside the analyzer’s info drawer, which slides out of the right-hand side of the analyzer’s window.
  14. Create a new Signal Generator tool.
  15. Select your DUT in the Output Device popup menu of the Signal Generator’s signal drawer (on the lefthand side of the Signal Generator window).
  16. Select the output channels corresponding to the physical output channels that you connected in step 2. Select the first output channel in the Left Output Channel box, and the second output channel in the Right Output Channel box. If you have connected more than two output channels for a multichannel measurement, you will need to create a new Signal Generator tool for each pair of output channels to be measured.
  17. Click on the Swept Sine (Chirp) tab in the Signal Generator window to display controls for establishing a frequency sweep excitation signal. Configure the swept sine generator as follows:
    • Frequency Sweep: Linear
    • Sweep Direction: Up
    • Lower Frequency: 0
    • Upper Frequency: 22050 or 24000 Hz (The Upper Frequency should be half the selected sample rate, which corresponds to the Nyquist frequency–22050 for 44.1 kHz sampling or 24000 for 48 kHz sampling.)
    • Duration: 8820 samples for 44.1 kHz sampling or 9600 samples for 48 kHz sampling
    • Repeat: Yes
  18. Click the “On” check box to enable the swept sine generator.
  19. Create a new Meter Bridge tool.
  20. Select your device in the Input Device popup menu of the Meter Bridge’s controls drawer (in the Live Inputs tab).
  21. Start the Meter Bridge.
  22. Make sure the Peak level type is selected in the Meter Bridge’s controls, then look to be sure none of the input channels are in danger of clipping (colored red at the top of the meter bar). If any of the input signal levels are too high, reduce the level in the Signal Generator.
  23. Select the FFT Analyzer window again.
  24. Start the FFT Analyzer, either by clicking the start icon in the window’s toolbar, or by selecting Start Analyzer from the Control menu (or by typing Command-R).
  25. Start the generator(s), either by clicking the start icon in the window’s toolbar, or by selecting Start Generator from the Control menu (or by typing Command-R). If you have one or more Signal Generator tools in your project, you can start all of them by selecting Start All Tools from the Control menu.
  26. After everything is running and the measurements have stabilized, you can stop the tools. (If you choose to stop the tools individually, rather than with the Stop All Tools command, it would be best to stop the FFT Analyzer tool(s) first.) Figure 2 shows a plot which shows the frequency response of the Echo AudioFire4. The frequency response of the AudioFire4 is quite flat between 20 Hz and 20 kHz.
    • For more advanced frequency response measurements, including phase response, coherence, group delay, and SNR, or to measure multiple audio devices simultaneously, please consider downloading Electroacoustics Toolbox.
  27. Capture your measurement, either by clicking the capture button in the FFT Analyzer’s toolbar, or by choosing Capture Data from the Control menu.
  28. Save your project so you can review your measurement or export the data at another time.
    Figure 2: Echo AudioFire4 Frequency Response


Are you looking for a measurement microphone for your iPhone?

Since iOS 6 finally remedied the low frequency roll-off problem of the headset mic input of the iPhone, iPod touch, and iPad, the headset jack has become a suitable option for measurement microphone input. Prior to the release of iOS 6, the only way to connect an external measurement microphone, without sacrificing low-frequency information, was to go through the dock connector. Dock connector devices can still provide higher quality solutions, but working with the headset jack offers a level of portability (i.e. compact size) that cannot be matched when a 30-pin dock connector is involved (we’ll see what comes along to take advantage of the new Lightning connector).

MicW i436

Some time ago, I was made aware of the i436 measurement microphone from MicW. It looked like exactly what was needed to turn any iOS device into a quality sound level meter, or acoustical analysis tool, that you could truly carry around in your pocket. However, it was limited in its utility by that pesky low-end roll-off that plagued earlier versions of iOS. Some developers attempted to perform software correction for the input filters, but when an input signal is driven into the noise floor by the hardware (or firmware), there’s nothing app software can do to restore the lost signal at those lower frequencies. Now that iOS 6 has solved the issue, the i436 has become the attractive measurement microphone solution for iOS that it should have been when it was first introduced.


Last weekend, I carried the i436 around the Denver Tech Center Marriott at the Rocky Mountain Audio Fest (RMAF), along with my iPhone 5. The i436 is small enough that it could slip into my pocket and remain there unnoticed or it could stay connected to the iPhone, which was perched in my shirt pocket when it wasn’t in my hand. In short, I was quite pleased to confirm that the i436 does indeed make for a portable measurement solution that you can carry in your pocket all day long.

MicW i436 Noise Measurement

As for quality, the i436 looks and feels like a proper measurement microphone. It was designed to meet the Class 2 standard for sound level meters, which addresses issues like environmental stability in addition to frequency response. The i436 also fits a standard microphone field calibrator, with a 1/4″ adapter, which you would also expect from a measurement microphone. A field calibrator makes microphone sensitivity calibration very easy with measurement software like SoundMeter or SignalScope Pro.

i436 Typical Frequency Responsei436 Typical Polar Pattern

The i436 is available in a package with just the mic, or in a kit. The kit includes a wind screen, extension cable, splitter cable (to connect headphones or an audio cable to the headphone output), a small clip, and an aluminum storage tube that doubles as a holder for the i436 that mounts to the top of a standard microphone stand (very handy).

i436 Single Packagei436 Kit Package

If Class 2 compliance meets your needs, then I highly recommend the MicW i436, especially in the kit. Either option is quite affordable for a quality measurement microphone. If you need a microphone that conforms to the Class 1 standard, then another hardware solution will be necessary.

iPhone 5 compatibility with existing audio input accessories

Since the Lightning to 30-pin Adapter (0.2 meter cable) arrived yesterday, I have had the opportunity to test several audio accessories with the iPhone 5. The results are presented below. Only accessories that worked with the iPhone 4 were tested, since earlier audio input accessories couldn’t be expected to work with the new iPhone (they relied on the analog input pins that were not supported on 4th generation iOS devices).

30-pin audio input accessory compatibility

Accessory iPhone 5 iPhone 4/4S
Apogee Jam Yes Yes
Fostex AR-4i Yes (1) Yes
Line 6 Mobile In Yes Yes
Sonoma Wire Works GuitarJack 2 Yes Yes
Tascam iU2 No (2) Yes
  1. There were a few times that I couldn’t get the iPhone 5 to recognize the Fostex AR-4i, but once it did, the AR-4i worked well. Sometimes, the iPhone would give the same message as that for the Tascam iU2 (below).
  2. When connecting the iU2 without USB power, the iPhone 5 wouldn’t recognize it. When USB power was supplied to the iU2, the iPhone would present a message which said, “The connected USB device is not supported.”

iPhone 5 audio consistent with iPhone 4S

Today, I had the opportunity to begin testing the audio input characteristics of the new iPhone 5. As seen in the plots, below, the headset input frequency response matches that of the iPhone 4S, which was presented in the previous post. The behavior of the built-in microphone also seems to match that of the iPhone 4S, suggesting that Apple kept the audio input path essentially unchanged in the new device.

One current limitation of the iPhone 5 is that existing dock connector accessories for audio input (and output) are not compatible, due to the iPhone’s new Lightning connector. As soon as Apple’s new Lightning to 30-pin adapter arrives, we’ll be able to see if it enables existing audio accessories to work with the new iPhone. Until then, the headset input and built-in microphone will have to suffice for iPhone 5 users. Fortunately, iOS 6, which comes installed on the iPhone 5, allows us to bypass automatic gain control and the high pass filter that plagued the headset input and built-in mic in earlier versions of iOS.

iPhone 5 Headset Leq iOS 6

iPhone 5 Headset Leq iOS 6 Fine Scale

IOScope 2.1 exports impulse responses to AIF, CAF, or WAV audio files

IOScope 2.1 is now available for download on the App Store.

IOScope room impulse response measurement

IOScope room impulse response measurement

IOScope 2 can now export normalized impulse response data to AIF, CAF, or WAV audio files. On iOS 5, or later, audio files can be previewed with IOScope or opened with other apps on the same device that can open these file formats. Of course, IOScope also allows for audio files to be transferred to a Mac or PC via iTunes File Sharing, or downloaded with a web browser via the built-in HTTP file server.

With IOScope, measure loudspeaker impedance, frequency response, and sensitivity. Measure a room impulse response. Tune a large sound reinforcement system, time-align a set of surround sound speakers, or optimize your home stereo. Determine the actual cutoff frequencies of your latest speaker crossover circuit, or teach your students the fundamentals of Fourier analysis of dynamic systems.

Measure frequency response magnitude and phase, coherence, and group delay. Time domain functions enable you to measure impulse response and auto/cross-correlation. IOScope includes a built-in signal generator for producing suitable excitation signals to analyze your system or device under test (DUT). The reference signal can be taken from the internal signal generator or from an external source (when using an external reference, a stereo audio input device, connected to the dock connector, is required).

IOScope also turns your iOS device into a platform for data acquisition, storing acquired data in CSV or tab-delimited text files, MAT-files, or images, including high-resolution PDF files, for later retrieval from your device.

What’s new in version 2.1?

  • Impulse responses can now be exported to AIFF, CAF, or WAV audio files. On iOS 5, audio files can be previewed within IOScope, or opened in other apps that support these file formats.
  • Frequency and time domain data can now be exported to CSV files, in addition to MAT-files and tab-delimited text files. CSV files can be opened directly in Numbers, or other spreadsheet apps that support it, from within IOScope.
  • The Excitation (signal generator) tab now supports the same color schemes as the analysis tools.
  • Other cosmetic improvements have been made to the user interface.

IOScope 2.1 requires iOS 4 or later, and is now available for download on the App Store for $74.99 (USD) in the Utilities category.

Learn more or download IOScope on the App Store

IOScope audio file export

IOScope audio file export

SoundMeter 3.0 offers in-app upgrades

  SoundMeter 3.0 is now available for download on the App Store,

offering in-app purchases of the same tools found in SignalScope Pro. Available upgrades include dual-channel Octave RTA, Oscilloscope, and FFT Analyzer tools, as well as a data acquisition upgrade.

Dual-channel analysis in the Octave tool enables SoundMeter to be used as a stereo 1/3-octave RTA. This dual-channel capability requires iOS 5, and is also coming soon to the Octave tool in SignalScope and SignalScope Pro, but it is available now in SoundMeter. (In SignalScope, the Octave tool is also available via in-app purchase.)

SoundMeter’s new data acquisition upgrade enables the user to export Octave, Oscope, and FFT data to CSV, tab-delimited text, and MAT files, and to access those files from a web browser on another device. This upgrade also enables additional units, such as V, A, g, and ips to be assigned to input signals.

Download SoundMeter 2

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