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Thursday, 7 January 2016

Cara Buat Masking table

Sebelum nak buat masking table, ada beberapa persoalan yang korang kena jawab


  1. had you derived the unmasked audiogram?
  2. mana satu better ear/non test ear and mana satu worst ear/test ear?
  3. mana satu telinga yang kita kena present tone and mana satu telinga yang kita kena present noise?
  4. mana satu telinga nak letak headphone, mana satu telinga nak letak bone vibrator?
  5. nak mask untuk which frequency?
  6. AC masking ke BC masking?
  7. berapakah initial presentation level untuk present tone and noise?


Untuk tahu dengan lebih lanjut, jom kita tengok contoh audiogram yang memerlukan kita untuk masking.



created using Audsim


SOALAN: IS THERE ANY MASKING NEEDED FOR FREQUENCY 1 KHz. IF YES, PLEASE DO  A MASKING TABLE.

STEP 1: JAWAB PERSOALAN-PERSOALAN NI

mana satu better ear and mana satu worst ear?
better ear adalah telinga kiri manakala worst ear adalah telinga kanan

mana satu test ear (TE) and  mana satu non test ear (NTE)?
memandangkan telinga kanan worst, so dia akan jadi kita punya test ear sebab of course kita nak test telinga yang worst, buat apa nak test telinga yang dah better kan. huhu

mana satu telinga yang kita kena present tone and mana satu telinga yang kita kena present noise?
test ear kena present tone and non test ear kita present noise sebab kita nak avoid partcipation of the non test ear

mana satu telinga nak letak headphone, mana satu telinga nak letak bone vibrator?

kalau buat BC masking, test ear kita letak BONE VIBRATOR and non test ear kita letak HEADPHONE (noise akan dipresent through headphone) tapi berlainan untuk AC masking, tone dan noise kedua-duanya akan dipresent guna HEADPHONE

nak mask untuk which frequency?

untuk soalan ni, dia suruh mask for 1 KHz kalau ade

AC masking ke BC masking?

untuk soalan ni akan ada masking diperlukan which is kita akan buat BC masking for 1 KHz sebab ikut Rule 2 different between AC HTL and BC HTL for test ear is more than 10dB

berapakah initial presentation level (IPL) untuk present tone and noise?

Tone - unmasked HTL (kalau AC masking, ambik AC HTL and if BC masking ambik BC HTL)
Noise - AC NTE + 10 dB



STEP 2 : LUKIS GAMBAR TELINGA ORANG

Lepas dah jawab semua persoalan kat atas tu, aku suka lukis gambar kepala orang sebab nak bagi nampak sikit proses masking tu. hihi



STEP 3: TAKE NOTE THE TRUE THRESHOLD and IAA
True threshold korang boleh tahu daripada masked audiogram. Just tengok dekat audiogram yang dah masked tu je. Untuk right ear, true HTL is 40 dB manakala for left ear, true threshold is 10dB. When we introduce 40 dB masking on the left ear, we are shifting the BC HTL of the NTE cochlea as much as 10 dB. Now, the BC threshold of the non test cochlea become 20dB sebab kita dah add up 10 dB noise from AC NTE. One more thing is Interaural attenuation (IAA). IAA for BC is ZERO. Jadi, sebagai contoh, bila kita present 10dB dekat telinga kanan, maka 10 dB jugak yang akan sampai kat telinga kiri. 

TRUE HTL RIGHT: 40 dB  [IAA = 0 dB]   TRUE HTL LEFT: 10 dB                                     

STEP 4: BUAT MASKING TABLE


PERHATIAN!! UTK EXPLANATION KAT BAWAH NI, AKU SUGGEST UTK KORANG BACA SAMBIL REFER KAT TABLE, KEPALA ORANG AND AUDIOGRAM YG DAH ADE KAT ATAS SUPAYA DAPAT TANGKAP APA YG AKU NAK SAMPAIKAN

Bila kita present 10 dB tone, telinga kanan takkan response sebab threshold dia 40 dB. Telinga kiri pun takkan response sebab threshold dia dah dishift kepada 20 dB.  Take note that, kalau TAKDE RESPOND, naikan tone sebanyak 5dB (masking noise tak perlu naikkan). Tapi, kalau ADE RESPOND, naikkan masking noise sebanyak 10 dB (tone tak perlu naikkan). Jadi, minimum response will come when we present 20dB tone and it comes from the NTE. If the response come from the NTE, that is what we called as UNDERMASKING.

Bila ade response, kita kena turn up the noise pulak. So sekarang noise is 50 dB and we shift the true BC HTL of NTE to 30 dB. Bila kita present 20 dB tone, telinga kanan takleh dengar sebab threshold dia 40 dB and the minimum response is when we present 30 dB tone and it comes from the NTE. It still undermasking. 

Bila ade response, kita turn up the noise lagi. So, sekarang noise is 60 dB and we shift the true BC HTL of NTE to 40 dB. Bila kita present 30 dB tone, dua dua telinga takleh dengar and the minimum response is when when we present 40 dB tone and it could be coming from both ears (sebab sekarang threshold both ears is 40 dB). 

Memandangkan kita still tak dapat lagi PLATEAU, kita kena increase lagi noise to 70 dB. Now, we shift the true BC HTL of NTE to 50 dB. Bila kita present 40 dB tone, test ear je response sebab NTE punya HTL dah shifted to 50 dB


Remember! Bila dah masuk je plateau, we need to be careful about OVERMASKING. If the noise and the tone at the same level, you can still hear the tone because that is the characteristics of the tone because the tone have more energy than noise eventhough the tone and noise is at same level.

When we present 90 dB noise, it cross over the skull to the test ear and now it starts to mask the test cochlea. Now, the true BC HTL of TE is shifted to 50 dB (overmasking).

RIGHT BC MASKING - BONE VIBRATOR ON THE RIGHT, HEADPHONE ON THE LEFT
THE INSTRUCTION
"okay cik, sekarang cik akan dengar bunyi beep dan bunyi hujan. Sama macam tadi, kalau dengar bunyi beep, terus tekan butang tu. Kalau dengar bunyi hujan, tak payah buat apa-apa" 

That's all. Semoga membantu. Kalau tersalah informasi, mohon betulkan ye. Thank you!

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Femmy