# De-Noising Process in Room Impulse Response with Generalized Spectral Subtraction
## 3 Implementation and Experiment  
### Experiment Design  
The investigation in this paper is carried out on real measured RIRs to analyze and confirm the performance of the GBSS algorithms and the feasibility of the subtraction factors implemented in de-noising RIRs. The measured RIRs are achieved in five different structure rooms to enable the GBSS algorithm to work on a real room case with various acoustic features.  
Three of the measured RIRs were used to determine the optimal factors contributing to the best dynamic range improvement. Artificial white and pink noises of different levels (from \(-65\) dB to \(-40\) dB with step \(-5\) dB) were added to the RIRs to have various dynamic ranges and SNRs. The reason for using these RIRs was because the wall reflection coefficients of the three rooms were different, and the background noise was low, which could be used to add artificial noises. Furthermore, the acoustic parameters achieved in low background noise were more accurate, enabling a reliable evaluation. Table 1 lists the detailed parameters of the three rooms. The anechoic chamber had a lower limit of the RT, providing a limiting case for the detecting algorithm [35]. The meeting room with 130 seats is made of perforated plates and a mineral wool sound-absorbing board. The hall was an empty but large room, similar to a classroom. The three rooms enabled tranquil environments where the noise levels estimated from the RIRs were less than \(-70\) dB. The values of the noise levels were estimated from the normalized energy time curve (normalized energy RIR) determined using iterative techniques [9].  
Once the sets of the factors were achieved, the RIRs measured in two normal rooms (room A and room B), listed in Table 1, were used to verify the accuracy of the obtained optimal factors of the GBSS algorithm (Section 4.4). In this case, the noise levels of the reference RIRs measured at midnight were approximately \(-60\) dB. In comparison, the RIRs measured in the daytime have natural ambient noise levels (including equipment noise) and were \(-40\) dB and \(-46\) dB. Strong sound reflection occurred in room A because the structure of the two walls was glass, resulting in a higher RT (1.32 s). Another room was the most normal room with an RT = 0.72 s. Six positions were used to test the RIRs in the hall, four positions in the meeting room and room A, while three positions were used in room B and one position in the anechoic chamber, yielding 63 conditions to verify the model.  
To evaluate the reference RTs for the five rooms, experiments were designed to follow ISO 3382-1:2009 [14]. In this experiment, an ABSWA MPA201 free-field microphone, which was connected to a SCIEN ADC 3241 professional sound card through a BNC connector cable to the adopted signal, was set beside the Bruel and Kjaer high-power omnidirectional sound sources. The loudspeaker was calibrated to eliminate the influence of distance in advance to generate a sweep signal, and the RIRs were measured by a measuring microphone that was added near the loudspeaker. An excitation signal with a length of 3 s was used for RIRs and computing was performed using MATLAB software. A length of 6 s was used for the hall due to its large volume. The measurement equipment used in the experiment had a flat response curve for a frequency range of 100 to 16,000 Hz. The volume of the signals was controlled by two INTERM L-2400 power amplifiers connected to a spoken connector cable. Professional software was used to record the noise level before taking the measurements.