we are having a great time on Musikmesse in Frankfurt and really enjoy our stay at the 5 elements hostel – it’s really nice!
we are having a great time on Musikmesse in Frankfurt and really enjoy our stay at the 5 elements hostel – it’s really nice!
For a visual representation of sound energy in different frequency bands it is necessary to transform the digital time domain audio signal into the frequency domain using a mathematical method: the Fast Fourier Transform (FFT). We will not explain the details here – the algorithm is well known and found in many publications and in Wikipedia as well. We will consider only a few aspects of the processes involved.
Digital audio data is represented in samples. The sample rate describes the number of samples which represent 1 second of audio, e.g. a sample rate of 44100Hz means that you need 44100 continuous samples to represent 1 second of your audio signal. The FFT works on blocks of samples which are power of 2, i.e. 256, 1024, 2048 samples coming up to 5.8ms, 23.2ms, 46.4ms at a sample rate of 44100Hz. Each “point” of the FFT represents the energy of a frequency range. Those ranges are linearly distributed over the entire range (0 – 22050 Hz @ 44100Hz sample rate). In our example with 256 points this would mean: the first FFT point represents all the energy between 0 and 172.3Hz whereas the last FFT point represents the range between 21878Hz and 22050Hz. The human perception of sound energy is logarithmic on the frequency axis. This means that the resolution of the lower frequencies computed with a narrow FFT block size is very unsatisfying because it leaves great gaps in the spectrum! One could argue that the solution to this problem is a larger block size like 65536 samples. Indeed this leeds to a FFT resolution of 0.67Hz per point which is quite satisfying. But: 65536 samples represent almost 1.5 seconds of audio! Despite the computational efforts there is no chance to get details on fast changes of the signal like in transients!
This relation between FFT block size and frequency resolution is the reason for the gaps in the Analyzer’s frequency view at lower block sizes. The shorter the block size the wider the gaps in the lower frequencies – we decided to leave those gaps as they are so you can always see how exact your analysis can be.
For further inside of the relation between block size and frequency resolution we can recommend this: http://en.wikipedia.org/wiki/Short-time_Fourier_transform
The FFT algorithms are based on periodic signals. A block taken out of even a periodical signal is not periodic – the FFT produces frequency leakage. To reduce this problem a window function is applied before calculating the FFT. This window “sharpens” the spectrum but may result in amplitude errors. Depending on the characteristics of the signal and the desired focus in the spectrum there are many different window functions. The Analyzer offers 6 of the most commonly used ones.
Here you can see the effects of different window functions on a 1000Hz sine:
important: if the Analyzer does not show any signal, please make sure that it has access to the built-in microphone here: settings -> privacy -> microphone
The Analyzer is an universal App designed to work smoothly on iPad and iPhone. Due to the different display sizes there’s only one main difference: while the iPad main view provides a frequency and a SPL Meter view on iPhone the SPL Meter view is available only in portrait mode. We integrated an autorotation lock function for the iPhone to prevent unwanted view changes.
The frequency view shows frequency over time graphs. An overview:
For accessing the menu respectively the properties of the graphs there are icons in the upper right corner:
The workspace is the summary of all snapshots and the actual graph. Touch the workspace icon and save the whole workspace (including color settings), export it, change the background color or remove it for clearing the display.
Save & export
Each snapshot and even whole workspaces can be saved in the Analyzers own proprietary data format. All records are listed in the menu under records. They can be loaded, shared via email or iCloud and exported to images (.png) or text files (.csv). When exporting a workspace to a png file all graph and background colors are preserved while the export of a snapshot creates a black on white picture.
Use thecog wheel in the upper right corner to access the menu. Here you can manage your records, change various settings, visit the store or make use of the sophisticated in-app help.
The left column shows your records. If you select a record a preview appears in the right column. It is zoomable like your main view. If you push the load button the graph shows in your main view. You can delete it, export it to .png or .csv files, send it via mail or move it between local storage (on your iDevice) or iCloud if activated. You can open and share .png and .csv files in appropriate Apps like FileBrowser or Dropbox.
If you want your records available on all your devices you can activate iCloud storage. Go to the iDevice settings -> Analyzer and turn iCloud to on. Now you can move your records between local storage and iCloud storage using the export function!
Audio IO settings
The Analyzer uses either the built-in microphone, an audio source attached to the headset input jack or any suitable USB class-compliant audio hardware attached via the dock connector. The iOS automatically detects which audio input and output are used. If the audio IO route changes the Analyzer automatically blends in the current audio route.
You can select input and output routing in this menu.
When a class-compliant USB audio interface is attached the Analyzer will work always on channel 1&2, 3-8 are not accessible at the moment. We tested successfully and can recommend: Apogee’s One, Duet and Quartet, the RME Fireface UCX, the Alesis IO dock and the Midiface Audioface II.
The frequency range defines the maximum range of the frequency (horizontal) axis.
A single band can either show the sum of energies of each FFT point between left and right border of the band (summed energy) or the mean over the whole band. This decision is made with the band filter mode setting. In sum mode a pink noise input shows a horizontal line and a white noise input shows a line with 3dB / octave rise. In average mode a pink noise input shows a 3dB / octave drop and a white noise input shows a horizontal line:
It is possible to view a normalized spectrum. If the normalization is activated, the level in the frequency view is always normalized to full scale.
The dB range defines the maximum range (dB) of the vertical axis. It is of course only available when normalization is deactivated.
The block size defines the length of the analysis interval.
With the reference frequency you define the “middle” of the frequency scale. Very common for measurements is 1000Hz. We added 440Hz also because this is the “musical” reference (A4).
With the window function you can influence the leakage of the FFT. Available are Rectangular, Hamming, Hann, Blackman, Blackman-Harris and Flat Top. For more information on fft & windowing go here.
Here are some properties and usages for the different window functions:
Here are the frequency responses of the iDevices running iOS6 via line in of the headset input (iPod touch 5 coming soon):
We made some measurements with the Analyzer 2 (beta version). As Apple disabled the built-in (software based) low cut in iOS 6 we are now able to get the responses of the iDevices directly (using the headset input). The results are great news: On iPad2 & iPad3 and iPhone5 the response is virtually flat from 20Hz – 20kHz! On iPhones 3GS, 4 and 4S there is still an attenuation of the lower frequencies which we will compensate for in Analyzer 2.0.
We made the measurements on different devices and shared them through the Analyzer’s new features: iCloud, png export, email and dropbox – that was fun! 🙂
Here are the graphs:
Analyzer 3.2 – now available with full support for iOS 13.x! It comes with Audiobus 3.x support including Audiobus state saving, Inter-App Audio support, a great graphic engine and unbelievable usability and functionality!
The Analyzer is a combination of a sound pressure level (SPL) meter and a full range multiple bands frequency analyzer. It is mainly designed for audio professionals who need to evaluate different working environments (e.g. studios, live stages)… that’s why it’s perfect for anyone who’s in need of acoustical analysis!! It is easy to use and comes with amazing features only known from professional acoustic tools.
Use the Analyzer for measuring stages, testing speakers, evaluate sound mixing environments, analyzing your instrument… or the noise your neighbor makes with his new stereo!
Combine the Analyzer with external microphones such as the Gefell M372 or the Mic-W i436 for better measurement performance! Or use it with external USB audio hardware like Apogee’s One, Duet and Quartet, the RME Fireface UCX or the Alesis IO dock, change the measurement scale to dB FS and use it as a studio Analyzer! Use the built-in signal generator for measurements – even wireless via Airplay!
The Analyzer supports Audiobus 3.x with Audiobus state saving, Inter-App Audio and offers frequency response compensations for these microphones: Apple Earphones, Apple Earpods, Apple In-Ear Headphones, Microtech Gefell M372, Mic-W i436, i266, i456, i825, i855, iShotgun, Røde iXY, Røde smartLav, Tascam iM2, Tascam iM2X – all available as In-App purchases.
Features of Analyzer 3.2:
We are working on a completely new version of the Analyzer (v2.0). It will take advantage of the new possibility to turn off the built-in lowcut (iOS 6 only). We also included real pinch zoom, snapshots, data storage and export, iCloud support, a much better graphic engine and many more exciting features! This major update will be available in a few weeks, hopefully still in october – we’ll keep you informed!
We are working on the Loudness App. It will be available again in the near future with an all-new functionality!!
Loudness provides loudness, loudness range and true peak level measurement for iPad2 & iPad3 according to the ITU RS 1770-2, ITU-RS 1771 and the EBU R128 and the EBU 3342 recommendations. In combination with a class compliant USB audio hardware like the RME Fireface UCX or the Alesis IO dock it turns your iPad into a qualified studio measurement tool. It comes with presets according to the most prominent recommendations of ITU and EBU and allows for completely user definable settings of many graphical and technical parameters. If you want to test Loudness you can check out Loudness Lite for a time limited fully functional version. Or just contact us!
– Loudness, True Peak and Loudness Range measurement according to ITU 1770-2, 1771 and EBU R128 and 3342
– simultaneous display of momentary / short term / integrated loudness and true peak level
– moving adjustable loudness over time graph showing momentary & short term loudness and gate level
– compatible with class compliant audio hardware
– tested & approved audio hardware: RME Fireface UCX, Alesis IO dock, Lexicon Omega, miditech audioface II
– manual and automatic calibration
– user adjustable algorithm parameters: gate levels, target levels, gate range
– user adjustable graphic engine: bar resolution, time resolution, absolute/relative scale, scale range, critical true peak level
– In-App help menu
The algorithms which are defined by EBU and ITU are computationally quite extensive. That’s why this App does not work on iPad1. The attached audio interface needs to be set to 48 kHz sampling rate.
We recommend to turn on airplane mode and turn off location services in the ipad settings for a smooth performance.
We have been working on this and the bug is fixed. An update has already been submitted to Apple and we are waiting for the review. The update comes along with some minor improvements and will probably be ready for download in the App Store in the beginning of next week.
Spectrograph is not available at the moment! We are working on a new version…
The Spectrograph displays and records spectrograms (visual representations of the spectral density over time) by processing the audio signal from the microphone input, Audiobus or Inter App Audio sources (iOS 7+) in realtime. It offers a 2D view and an amazing 360 degrees fullscreen 3D view. The Spectrograph is a universal app for iPhone and iPad.
Use the Spectrograph for studying music, animal sounds, voices and speech or just have fun with the beautiful visualization of environmental sounds! Make use of the ability to store and load spectrograms and even reprocess them with different settings for discovering new details in your recordings!
– 2D view with control panel for record, free run and store
– 3D view (free run only) with touch gesture controls of the viewing angle
– free choice of bandwidth / number of frequency bands (depending on your iDevice up to 800!)
– 3 buffer sizes: 1024 / 2048 / 4096 samples
– 3 gain modes for getting the best out of every acoustical situation
– 6 different color schemes
– logarithmic time frequency scale (detachable with one touch on screen)
– record spectrograms (recording time between 30 seconds and 2 minutes – depending on your iDevice)
– record preroll
– reprocessing of recorded spectrograms
– compensation for the low cut of the built-in microphone and selected external microphones utilizing the input jack (available as in app purchases)
– detailed help section within the Spectrograph with no need for internet connection