Adapting Villchur s loudspeaker-copying-loudspeaker demonstrations to earphones

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1 Adapting Villchur s loudspeaker-copying-loudspeaker demonstrations to earphones Mead C. Killion, Ph.D. Sc.D.(hon) CTO and founder, Etymotic Research, Inc. Adjunct Professor of Audiology, Northwestern Un. ALMA International 2012 Winter Symposium January, 2012 Las Vegas

2 ABSTRACT Edgar Villchur used to enjoy demonstrating that an AR-3 loudspeaker could reproduce the sound of a popular ElectroVoice loudspeaker, but the latter could not reproduce either the AR-3 or itself. A similar technique for use with earphones has the advantage of not requiring such a careful choice of microphone locations, but the disadvantage of requiring equalization of the eardrum pressure response on KEMAR. By use of several probe-microphone studies of the diffuse field response of the ear, plus a Chicago AES-meeting listening-test confirmation of previous reports that most commercial recordings contained a highfrequency pre-emphasis (from electronics or choice of microphones), a target response curve was derived. Thus armed, an inverse filter applied to KEMAR recordings allows a true high-fidelity earphone to reproduce a reproduction of itself with little audible difference. Some popular earphones do not fare as well.

3 When you purchase a color copier, you expect it to reproduce the colors of the original.

4 Actual results from a fairly good color copier: Original Copy

5 A more sensitive test can be made if we make a copy of a copy Original Copy Copy of Copy We can use a similar test with earphones.

6 It is unlikely that a color copier would be designed to intentionally distort colors, but if it did, a second generation copy highlights the distortion. Original picture More red, more blue! Do it again!

7 Nor is it likely that a stereo amplifier or mp3 player would be designed to intentionally distort the frequency response. But most earphones appear to have been designed to do so. This becomes doubly obvious using Villchur s audio-copy method to make second-generation copies.

8 Coloration in an image is easily seen when compared to the original. Coloration in sound is easily heard when compared to the original.

9 Q: What happens if two boomy earphones are recorded one from the other? A: The midrange sounds disappear. Copy 2 Copy 1 Fagin: Ruby Ruby Bach: T&F Dm Peterson Grapelli Original

10 Q: What happens if you listen to two highaccuracy earphones in series? A: You can hear little difference: Which is the basic definition of high fidelity faithful to the original

11 Bach: T&F Dm Fagin: Ruby Ruby Peterson Grapelli Original sound Copy sounds the same Even the second copy sounds the same

12 Examples of some earphones tested last year (Etymotic Research KEMAR tests, independently confirmed by Elliott Berger at EAR-CAL laboratories)

16 Lest you think earphones are the only examples of low-fidelity design, consider the sound of a $4,000 pair of hearing aids about to be introduced.

17 KEMAR THE PIANO PLAYER (2008 picture, 2011 recordings) Once in a While Open Ear -- New Digital Aid Q Boogie Open Ear -- New Digital Aid Q Each live A-B comparison was obtained from the sound simultaneously recorded in the left and right ears of the KEMAR manikin. In most cases, the left ear (B) had a digital hearing aid in place, while the right ear (A) ear was open or had an analog hearing aid (K) in place

18 M Q

KEMAR THE PIANO PLAYER (2008 picture, 2011 recordings) Once in a While Open Ear -- Present Digital Aid M Boogie Open Ear -- Present Digital Aid M Each live A-B comparison was obtained from the sound

19 KEMAR THE PIANO PLAYER (2008 picture, 2011 recordings) Once in a While Open Ear -- Present Digital Aid M Boogie Open Ear -- Present Digital Aid M Each live A-B comparison was obtained from the sound simultaneously recorded in the left and right ears of the KEMAR manikin. In most cases, the left ear (B) had a digital hearing aid in place, while the right ear (A) ear was open or had an analog hearing aid (K) in place

20 Trumpet Open Ear -- New Digital Aid Q (2008 picture, 2011 recording)

21 Always warm up I didn t! Bach Dm Partita Gigue Open ear Hearing Aid M

EDIROL 24-bit Digital Recorder Record earphone output signal from previous earphone output recording COPY 2 KEMAR manikin

22 RECORDING STEPS FOR MAKING 1 ST AND 2 ND COPIES OF EARPHONE OUTPUT Record original signal ORIGINAL SIGNAL ipod music source EDIROL 24-bit DIGITAL RECORDER Record earphone output signal COPY 1 ipod music source Two ER-11 ½ Mic Preamp and DFI Filter EDIROL 24-bit Digital Recorder Record earphone output signal from previous earphone output recording COPY 2 KEMAR manikin with Zwislocki Couplers in ears EDIROL 24-bit Digital Player Two ER-11 ½ Mic Preamp and DFI Filter EDIROL 24-bit Digital Recorder

23 Note: The correctness of the original diffusefield-inverse filter is crucial for accurate copy demonstrations. Q: What is the reference for the Accuracy Scores? A: The average Diffuse-Field response of the human ear Three Scientific Studies: Shaw, Killion and Monser, Berger et al. But the first major study was free-field: Wiener & Ross (1946)

26 1946 stainless steel probe tube 1986 soft silicone probe tube

27 J Audio Eng Soc (1979)

29 Q: Do you use the inverse dfi filter directly, or do you modify it for earphone recording to take into account the pre-emphasis built into all CD recordings (by filtering or, with direct-to-cd recording, by microphone choice). A: We use the modified response. We use the inverse of our 1992 earphone target curve, which is reduced from the pure diffuse-field target by 5 db at 10 khz

30 The whole story of the 5 db: We learned the hard way. Our original ER-4 earphones matched the diffusefield target almost exactly. I confirmed that we had done it right with live-vsrecording experiments with the choir I direct every Thursday and Sunday. I could listen directly and listen through the earphones and was convinced we had done it right. We introduced what we now call the ER-4B version of our earphones, but after about the fifth complaint that our new earphones were too bright, I locked myself in the office one morning with 12 CDs, six of them of groups I had heard live within the previous year. They were right. I subsequently found papers by Schulein, Toole, and others which confirmed the pre-emphasis in CD recordings. Schulein went to the extent of measuring the response of popular studio monitor setups in Chicago, and found they had an average of 5 db rolloff at 10 khz, just like the room response of better home loudspeaker systems. We confirmed that 5 db was the about the right value in a listeningtest experiment at a Chicago AES meeting some years ago.

31 Q: Any other indication that you did the right thing? A: I think so. I was invited to Tom Holman s 60 th birthday party a few years back, and we started discussing the issue and he gave me a copy of his THX curve which is now internationally standardized for movie theatre sound.

32 KEMAR Eardrum Response in db Comparison of KEMAR Target Responses: THX vs. Etymotic Earphone Target THX (Tom Holman X curve ) is the ISO-2969 Standard KEMAR target for all Dolby Theatre installations THX KEMAR Target 1993 Etymotic Target Frequency in Hz

33 My impending ALMA talk here today motivated a new set of recordings in our diffuse-field chamber, just to be sure.

34 Did we get it right years ago? A 2012 re-check Bill Withers Spaced ER-11 ½ mics Charles Aldous Engineer who likes Bill Withers

35 Unfiltered eardrumposition ER-11 mics Original: Spaced ER- 11 Mics With dfi filter

36 Bach: Tacata and Fugue in Dm Unfiltered eardrumposition ER-11 mics DFI filtered eardrumposition ER-11 mics ER-11 mics in sound field ER-11 mics in sound field

37 Fagan: Ruby Ruby Unfiltered eardrumposition ER-11 mics DFI filtered eardrumposition ER-11 mics ER-11 mics in sound field ER-11 mics in sound field

38 Sometimes, the most important part of earphone performance is blocking the outside noise. Etymotic Earphones have the best noise exclusion we know of confirmed by tests at the independent EAR-CAL in Indianapolis, Indiana, a laboratory reputed as the best in the world for testing noise exclusion earplugs.

39 The following self-serving observation is not part of the technical presentation, but is blatant promotion.

40 The next slide has a lot of curves, because we asked Ear-Cal laboratory to test all the important earphones we knew of. hold on

41 Better Noise exclusion (in db) ER-4 3-flange ER-4 foam ER-6i 3-flange

43 References for Diffuse-field Target Response for High-Fidelity Earphones Allison R and Berkovitz R (1972) The sound field in home listening rooms. J Audio Eng Soc Vol. 20: No. 6 (July/August) pp Allison R (1976). The sound field in home listening rooms, II. Presented November 3, 1975 at the 52nd Convention of the Audio Engineering Society, NY. Published in J Audio Eng Soc Vol. 24, No. 1 (Jan/Feb) pp Block MG, Tillman TW and Killion MC (2004) The Missing 6 db of Tillman, Johnson, and Olsen was found 30 years ago, Seminars in Hearing, 25, No. 1, Bridges S (1980). Effect of direct sound on perceived frequency response of a sound system. Presentation at the 66th Convention of the Audio Engineering Society, Los Angeles, CA. Fletcher H (1953). Speech and Hearing in Communication VanNostrand reprinted by Kreiger NY (1972) and Acoustical Society of America (ed Jont B. Allen), Woodbury, NY (1995). Harvard (1971). The Harvard Project Physics Course Reader (1971), Unit 4 Light and Electromagnetism, Holt, Rinehart and Winston, Inc., New York, NY, Holman T (2007). Personal communication. Killion (1978). Revised estimate of minimum audible pressure: Where is the Missing 6 db? J Acoust Soc Am 63, Killion MC (1979). Equalization filter for eardrum-pressure recording using KEMAR manikin, J Audio Eng Soc 27: Killion MC (1984). New insert earphones for audiometry, Hearing Instruments 35, No. 7, 28. Killion MC, Berger EH and Nuss RA (1987) Diffuse field response of the ear. Presentation at the Spring 113th ASA Meeting, JASA Suppl. 1, 81, S75, May 14. Lybarger SF (1978). Selective amplification A review and evaluation. J Am Audiology Soc Vol. 3, No. 6, pp Martin DW and Touger ML (1950). Loudness balance methods for earphone response measurements. Vol. 22, No. 6 (Nov.): Olsen HF (1967). Music Physics and Engineering Dover, NY Reite D (2007). Schulein RB (1975). In situ measurement and equalization of sound reproduction systems. J Audio Eng Soc 23: Rudmose W (1982) The Case of the missing 6 db. J Acoust Soc Am Shaw EAG (1990) Estimate of sound pressure transfer from the diffuse sound field to the eardrum. Personal communication based on his own previous studies (Shaw EAG (1973) Sound pressure transformation from the free field to the eardrum J Acoust Soc Amer 53:291 and Shaw EAG (1974). Transformation of sound pressure level from the free field to the eardrum in the horizontal plane. J Acoust Soc Amer 56:1848.) Toole FE (1974). Fidelity: Just what should monitor speakers be faithful to? AudioScene Canada, October, pp 46, 53, 56, 59. Toole FE (1977). Speakers: Parts One-Four. AudioScene Canada March, pp ; April, pp , 51; May, pp , 52-54; July, pp Villchur EM (1957). Handbook of Sound Reproduction. Audio Library Vol. 3, Radio Magazines, Inc., Mineola, NY. Villchur EM (1964). Techniques of making live-versus-recorded comparisons. Audio pp , 120. Villchur More recently, Viranyi S, Iseberg I and Wilson D (1993). What is the proper frequency response of an earphone? Presentation at the Chicago Midwest Acoustical Engineering Society Meeting, June 9, Wilson D, Iseberg S, Viranyi, S, and Killion M (2006). Choice of high-frequency equalization in Etymotic Research insert earphones. Update (May 24, 2006) of a presentation at the AES meeting held at the WFMT studios June 9, Weiner FM and Ross DA (1946). The pressure distribution in the auditory canal in a progressive sound field. JASA Vol. 18, No. 2 (Oct.), pp

44 Questions?

INTRODUCTION TO PURE (AUDIOMETER & TESTING ENVIRONMENT) TONE AUDIOMETERY. By Mrs. Wedad Alhudaib with many thanks to Mrs.

INTRODUCTION TO PURE (AUDIOMETER & TESTING ENVIRONMENT) TONE AUDIOMETERY. By Mrs. Wedad Alhudaib with many thanks to Mrs. INTRODUCTION TO PURE TONE AUDIOMETERY (AUDIOMETER & TESTING ENVIRONMENT) By Mrs. Wedad Alhudaib with many thanks to Mrs. Tahani Alothman Topics : This lecture will incorporate both theoretical information