fft & windowing

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:


snapshots show from left to right: flat top – Blackman-Harris – Blackman – Hann – Hamming – rectangular

left to right: rectangular - Hamming - Hann - Blackmann - Blackman-Harris - flat top

zoomed in from left to right: flat top – Blackman-Harris – Blackman – Hann – Hamming – rectangular

Analyzer support

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.

Main view

Navigation and zoom are provided using the usual touch gestures:



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:

mainView_icons@2x Snapshots
The Analyzer offers the possibility to take snapshots of frequency over time graphs (depending on your device up to 14). A snapshot is created if you start a Leq measurement, press the hold button or the snapshot button. Each snapshot has its own bar / line graph, an icon (which represents a live updating miniature of its corresponding graph) and it’s unique color. Touch the icon to save, export, clone, change color or remove the corresponding snapshot.


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:

band filter mode_sum_enband filter mode average_en

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).

Window functions

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:





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 OneDuet 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:

    • Inter-App Audio support
    • Audiobus 3.x support including Audiobus state saving
    • improved compatibility with all iOS devices
    • multiple language support starting with english and german
    • reticle with lens functionality
    • bar or fft line view
    • user definable graph colors
    • optional automatic peak detection
    • optional equal loudness contours
    • data storage
    • export to .csv oder .png files: share them via Mail, Dropbox and other Apps
    • up to 14 different snapshots (depending on the iDevice)
    • advanced iCloud support
    • zoom like in maps
    • data storage, import and export
    • advanced iCloud support
    • up to 14 different snapshots (depending on the iDevice)
    • workspace
    • select your bandwidth from 1octave up to 1/1200 octave (depending on your iDevice)
    • choose between 6 different window functions
    • select your FFT block size from 1024 to 65536 samples
    • In App help without the need of internet connection
    • signal generator (white/pink noise, sine)
    • frequency response compensation for different mic characteristics of the built-in microphones
    • switch between dB (FS) and dB (SPL) level (headset / USB in only)
    • switch between normalized and absolute frequency levels
    • manual and automatic calibration
    • Leq measurement
    • weighting functions: A B C Z
    • 3 different response times
    • audio input / output setup
  • frequency response compensations for 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



LoudnessWe 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 screenshots:

Loudness features:

– 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

Technical notes:

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.



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!

Spectrograph features:
– 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

Spectrograph screenshots:

beat detector

Beat Detector is not available at the moment. we are working on the all-new Beat Detector 3 – hopefully it will be available soon!
The new Beat Detector 2.0 detects the tempo of the music in BPM (Beats Per Minute) continuously in realtime. It will be available very soon – it is already in review at iTunes!
It displays the 4 most probable BPM results, their predecessors and a corresponding rhythm pattern. It comes with a great GUI: its color coding illustrates the relationship between detected BPM values and the rhythm pattern energies. Previous values flow away in a smooth animation. The Beat Detector supports Inter App Audio, Audiobus and Airplay and is already optimised for iOS 8.The Beat Detector works on audio signals coming through the microphone, any attached audio hardware or Audiobus / Inter App Audio.The Beat Detector calculates it’s current result by analyzing previously measured BPM values going back to 20 seconds. Tap the display once to reset this memory and restart calculation.
Beat Detector features: – automatic realtime beat detection – innovative GUI showing the 4 most probable BPM values, a timeline and corresponding rhythm pattern – automatic input level gate – Audiobus and Inter App Audio support – Airplay support – full iOS 8 support
Beat Detector screenshots: 

Analyzer update 1.0.2 available

Our update is available in the App Store! We fixed the latency issue and added facebook integration – now you can post your noise levels directly!

Get the update here:

dB Volume

dB VolumeWith dB Volume you turn your iPhone / iPod touch into a Sound Pressure Level (SPL) Meter. You can choose between the industry standard weighting curves and response times. If you use headphones, unmute your device to listen to the noise!

Measure the sound of your environment and share it directly via facebook – your friends will know how loud you had it!

dB Volume features:
– response time modes: impulse, slow, fast
– weighting functions: A B C Z (unweighted)
– peak hold function
– mute function

We calibrated dB Volume as carefully as possible for all available devices. But: keep in mind, that due to manufacturing tolerances this calibration does not necessarily apply to your device – it’s still an iPhone, iPod touch or iPad and not a calibrated measuring instrument!