Smartphone Specs
The Samsung Galaxy A50 is equipped with two microphones – a front microphone and a back microphone. Both of these microphones can be used for recording (depending on the software in use). If Samsung’s built-in software called ‘Voice Recorder’ is used, only one of the microphones is utilized. The other microphone is meant to boost noise cancellation. However, softwares like RecForge II – Audio Recorder give you the option to choose between the two microphones. The Galaxy smartphone also offers stereo input options. Stereo input options can be accessed via RecForge’s ‘Audio Record’ settings. The options available are Mono and Stereo(Mono x 2). The maximum sample rate for both microphones is 48kHz. Due to insufficient information on smartphone specification websites, the audio samples were loaded on QuickTime player and were inspected using ‘Movie Inspector’. Movie Inspector showed the format of the audio samples as ‘16-bit little-endian signed integer’ from which it can be deduced that the bit depth is 16.
Audio Recording Applications
In the pursuit for an Android recording app which records uncompressed audio in .wav and disables AGC, one may stumble upon the following: Tape Machine, Smart Recorder, and RecForge II.
While Tape Machine has a heavy fan-base on developer blogs and forums, it isn’t available from download anymore. It was hailed for having the AGC disablement feature.
Smart Recorder is best at what it’s meant for – recording audio. Though it allows the user to disable AGC and records in .wav, the sampling rate maxes out at 44.1Hz. Apart from this it also doesn’t offer many basic audio editing features.
In comes RecForge II – a well designed, user friendly software, allowing users to disable AGC and set a sampling rate to the maximum limit of their hardware. The application supports nearly all audio formats and offers a range of various editing tools including (but not limited to) Acoustic Echo Canceler and Skip silence. Going forward, RecForge II has been used alongside the frontal microphone to record all audio files.
Generation of Sine Sweep and White Noise
The software used was Audacity. First, In Audacity’s Generate menu a Chirp was produced in the shape of a sine wave for 15 seconds. Next, using the same Generate menu, the Noise plug-in was used to generate 15 seconds of white noise.
Recording Using Phone Microphone
For each 15-second sound, 3 recordings were made using the phone (six recordings in total). For the first recording the phone was placed on the laptop’s keyboard. In the second recording the phone was kept approximately 8 cm away from the laptop’s keyboard. Finally, in the third recording the laptop was placed inside a cupboard (a restricted space) and the phone was placed on the laptop’s keyboard. Gain used for all recordings was +9.0dB.
Analysis and Understanding
Using ‘plot spectrum’ function in audacity, the following graphs were plotted for sine sweep.
All of the sine sweep graphs have one thing in common – they consume a healthy portion of the plot. The first plot is consistent and flat in terms of the relative responsiveness (expressed in dB). However, when a phone is used, the plots change and a deformed shape emerges. A change in the range of dB clearly shows that there has been a change in sound quality. When the phone is closer to the keyboard, a greater number of peaks are observed at higher frequencies. In a way we could say that being close to the keyboard ‘boosts’ the responsiveness of the microphone (same goes for enclosed locations such as cupboards). If you listen to the recordings, the recording done on the keyboard is much louder and clearer than the recording done 8cm away from the keyboard. However, the recording done in the cupboard is a louder, amplified version of the recording done on the keyboard. This can clearly be seen in the graph as at higher frequencies the 4th graph has more peaks than the 2nd graph.
Using ‘plot spectrum’ function in audacity, the following graphs were plotted for white noise.
Compared to the sine sweep plots, the white noise graphs consume less area on the plot. The first white noise plot has various peaks however they are much lower than the flat crest observed for the initial sine sweep. By the introduction of taller peaks in the phone recorded graphs we can observe that the phone recording has severely impacted the sound quality of the white noise. Such a drastic change in peak height was not observed in the plots for sine sweep. For white noise, the change in loudness is the same as sine sweep in the sense that the more enclosed the environment and the closer the microphone to the sound source, the louder the recording. This can be observed by how the number of peaks at higher frequencies tend to get more in number and taller as the microphone is placed in a cupboard or is moved closer to the sound source.
To draw a conclusion we can say that the loudness of the recording is inversely proportional to the size of the room and the distance of the microphone from the sound source. However at the same time the loudness is directly proportional to the number and height of the peaks at higher frequencies.
As far as the spectral flatness of the microphone is considered overall, we can say that the microphone produced ‘shaped’ curves. This suggests that the microphone is more sensitive to certain changes in frequencies than others. This can be seen by the fact that lower frequency areas tend to have fewer peaks, whereas higher frequencies portray more peaks, clearly showing that the microphone is more responsive to higher frequencies (typically above 3000Hz, as seen on all graphs).
Recordings: https://drive.google.com/file/d/19jfF4ezgNVOPLkGrbufHGzcD6oLoKwju/view?usp=sharing
Sources
https://forum.xda-developers.com/showthread.php?t=1042051
https://www.shure.com/en-US/performance-production/louder/mic-basics-frequency-response
https://filmora.wondershare.com/audio-editor/best-voice-recording-apps-android.html
https://support.ebird.org/en/support/solutions/articles/48001064305-smartphone-recording-tips
https://www.neumann.com/homestudio/en/how-does-frequency-response-relate-to-sound
https://www.gsmarena.com/samsung_galaxy_a50-9554.php
https://www.thepodcasthost.com/recording-skills/best-audio-recording-apps-for-android/
I never knew that only one of the microphones was used for “Voice Recorder”, and that the other was meant to boost noise cancellation! I’m curious about how “Voice Recorder” would perform — what would the graphs look like?
Interesting to see how microphones from Galaxy products compare to those from Iphone products. Both seem to possess a good level spectral flatness when the microphone is close to the source of sound, and possess somewhat the same dips and peaks when farther away from the source. At a glance, seems as though the microphones between the two brands are mostly similar.