HRTF’s and Reverberation

This project aimed to study Bin­au­ral Room Impulse responses, sim­u­late the impulse response of a shoe­box room using the image method.

The image method was pro­posed by Allen and Berke­ley, access the paper here.

Read on for a crash course in the image method. (The fol­low­ing fig­ures were taken from this link.)

In a rec­tan­gu­lar room, the sound you hear con­sists of two com­po­nents. The first is the orig­i­nal sound, the sound waves trav­els directly from source to the lis­tener, as shown in the fig­ure below.

Image Method — Direct Sound

 

The sec­ond com­po­nent, con­sists of reflec­tions of the sound from the walls, floor and the ceil­ings. These are delayed and amplitude-scaled copies of the orig­i­nal signal.

Image method — Early Reflections

Using the Head Related Trans­fer Func­tion (HRTFdata­base from the MIT Media Lab, I imple­mented and extended a sim­pli­fied ver­sion of the above method to account for direc­tional infor­ma­tion of the vir­tual sources.

The result is audi­bly and vis­i­bly dif­fer­ent from a con­ven­tional room impulse response, but is far more expen­sive com­pu­ta­tion­ally. Near­est neigh­bor inter­po­la­tion was used on the HRTF’s, more com­pli­cated meth­ods increased the com­pu­ta­tional com­plex­ity with­out sig­nif­i­cant audi­ble improvements.

The results for two sim­u­lated responses are dis­played below. In both results, the sam­pling rate was set to 44.1 KHz, the reflec­tion coef­fi­cient of the walls was set to 0.3, the speed of sound is set to 343 m/s, and orders of reflec­tion up to 4 were con­sid­ered. The only vari­able that was changed was the dimen­sions of the room and the loca­tion of the mic and the source. Please use head­phones for the audio examples.

Sim­u­la­tion 1:

Room size : 40m X 40m X 40m

Mic posi­tion: (4m,3m,1m)

Source posi­tion: (40m,20m,30m)

BRIR_result_1

Results of sim­u­la­tion 1 (click for a larger picture)

Orig­i­nal Audio Source :

Out­put of con­ven­tional image method:

Out­put of Bin­au­ral extension:

 

Sim­u­la­tion 2:

Room size : 4m X 4m X 4m

Mic posi­tion: (4m,3m,1m)

Source posi­tion: (4m,2m,3m)

 

Results of simulation -2

Results of sim­u­la­tion — 2 (Click for larger picture)

 

Orig­i­nal Audio Source :

Out­put of con­ven­tional image method:

Out­put of Bin­au­ral extension:

 

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