Samsung’s Galaxy Note 9 has two microphones: one at the top of the phone and another at the bottom of the phone. However, Samsung’s default Sound Recorder app was only capable of recording using one microphone instead of both. Unfortunately, the sample rate and the bit depth of the phone’s microphone was unable to be detected. However, when RecForge to record audio, I was able to use the settings to record at at 48khz at bit rate of 24, thus it is assumed that the Galaxy Note 9 have at least these specifications.
Audio recording apps that I had tried to use included Samsung’s default voice recorder, True voice recorder, and finally RecForge. As mentioned above, Samsung’s default application only utilized one of the speakers. It was determined that, after doing a mic-covering test individually on each mic, that the application only used the bottom mic. A similar test was conducted on True Voice Recorder. Though this application allowed me to adjust the Audio Gain, it nonetheless only recorded through one microphone. RecForge, however, was able to utilize both top and both microphones on the phone, which I tested by moving the phone above and below a sound source and tested if playback matched the anticipated movements.
Audacity was used to generate both sounds. The 15 second rising pitch from 100 Hz to 18 kHz was was accomplished by using Audacity -> Generate -> Chirp function. The 15 second white noise was generated by navigating to Audacity -> Generate -> Noise -> White Noise.
My computer, the 2019 Razer Blade Stealth, had stereo speakers with a speaker to each side of the keyboard. When recording the sound onto my computer, I placed the phone just above the middle of the keyboard, equidistant from each speaker. The phone’s top speaker faced the left side, while the phone’s bottom speaker faced the right side. It should be noted that this orientation should not have affected the sound much, as the sounds generated on Audacity were both mono.
After recording the audio on my Galaxy Note 9 using RecForge in the .wav format, I emailed the files directly to myself and downloaded them onto my Razer Blade Stealth for analysis.
From the two illustrations above, we see that the compared to the original file, the the recorded audio file had less amplitude, with the former maxing out at -12.5 dB and the latter at -24.5 dB (higher decibel = louder). In addition, we also see the maximum amplitude of the original audio file occurs at 150Hz, while the maximum amplitude of the original recording recorded a maximum amplitude at 600 Hz. This data seems to suggest one, or a combination, of three possible conclusions
- The Galaxy Note 9 microphone is more sensitive to higher frequencies that is it to lower freqencies
- The Razer Blade Stealth’s speakers are better at projecting higher frequencies that is it at lower frequencies
- The medium (air) is better at transmitting Higher frequencies than lower frequencies
The third conclusion is least likely to be a factor, as-frequency sounds are generally better at traveling through medium that high-frequency sounds.
For further analysis of the potential cause of this difference, we now perform a side-by-side comparison of the white noises.
From analyzing the white noise graphs, we see that the peak amplitude on the original white noise graph was -28.9 dB, while the peak amplitude on the recorded white noise graph was at -44.2 dB. However, the frequencies at which the peak sound was heard are remarkably similar, at 365 Hz and 371 Hz respectively. Unfortunately, the lack of peak amplitude difference between the original and recorded audio presents us with no information that could help us diagnose which of the three hypotheses could be contributing to the difference in frequency of the maximum amplitude.
Another point of interest for us to analyze would be how distance between the microphones and the speaker changes the maximum amplitude and the frequency at which it was observed.
Above are the FFT analysis of the audio recordings on the Galaxy Note 9 at 4 different height above the computer keyboard (in the same orientation as described above). Their respective peak amplitude at corresponding frequencies are as follows: -26 dB at 7000 Hz, -34 dB at 4000 Hz, -25.3 dB at 7000 Hz, and -25.7 dB at 7000 Hz. After considering our 8cm test as an outlier (the dB and frequency are definite outliers compared to the other data points), there seems to be no correlation between distance from speakers, maximum dB, and maximum frequency. However, with respect to our original three hypothesis, this does indeed rule out the possibility that the different frequency observed is due to the medium: even with increases in medium distance, there did not seem to be any difference in frequency at which the maximum amplitude was recorded.
Overall, when comparing the first two graphs, I am convinced that the Galaxy Note 9 has quite a flat frequency response. In the first two graph comparison between the original audio recording and the recorded audio of the 100-18000Hz sine sound wave, the approximate shape of the two graphs were quite similar, with the only difference between the two being that the latter had greater inconsistencies (dips and ridges) in the peak decibel of each frequency. This is likely due to environmental interference, such as sound waves bouncing off the walls in my dorm room. In a future analysis, it would indeed be ideal to complete the experiment again in a sound-absorbing environment, such that it reduces the environmental effects on the sound waves picked up.