AES Journal Forum Comments

AES Journal Forum: Comment by Earl Vickers on "The Loudness War: Do Louder, Hypercompressed Recordings Sell Better?"

Tue, 07 Feb 2012 09:31:38 -0700

Title: The Loudness War: Do Louder, Hypercompressed Recordings Sell Better?
JAES Volume 59 Issue 5 pp. 346-351; May 2011
Comment by: Earl Vickers

At the 2011 New York AES Convention, Susan Rogers gave an interesting presentation (audio available from the AES store), that referenced and occasionally questioned my papers on this topic. While I disagree with some of her conclusions, I'm rethinking the issue of dynamic range compression and hearing loss.

My paper made the traditional assumption, as embodied in the ISO1999 standard, that hearing damage is proportional to cumulative energy exposure; this would suggest that compressed music is likely to be more damaging, since it spends more time at higher levels. However, Rogers quotes Gerald Fleischer, "Strategies of the Hearing System Against Noise and Auditory Damage," in Reflections on Sound, Svensson, P. (Ed.), 2008, who states that hearing damage is more likely to be caused by short impulsive noise than by ongoing continuous noise, due to the ear's protective mechanisms. To the extent that dynamic range compression reduces the relative level of impulsive peaks such as drum hits, it may in fact serve a protective function. However, this is a hard thing to test. At any rate, this effect applies mainly to fast (microdynamic) compression, not to compression with slower time constants (equalizing the levels of verse & chorus, etc.).

Regardless of the effect of hypercompression, I think the weight of the evidence strongly suggests that extended headphone and ear bud listening at high levels can be harmful, particularly in regard to tinnitus. (More at http://www.sfxmachine.com/docs/loudnesswar/ .)

AES Journal Forum: Comment by Nay Oo on "Perceptually-Motivated Objective Grading of Nonlinear Processing in Virtual-Bass Systems"

Sat, 04 Feb 2012 12:18:08 -0700

Title: Perceptually-Motivated Objective Grading of Nonlinear Processing in Virtual-Bass Systems
JAES Volume 59 Issue 11 pp. 804-824; November 2011
Comment by: Nay Oo

Thank you again for your interest and questions.

Q1) In Aarts's article, HPF2 and LPF have the same cut-off frequency. This is a logical choice, since their intention was to evaluate the added value of the harmonics components on bass perception. In your article, HPF2 and LPF have cut-off frequencies of 100 Hz and 280 Hz respectively. What did motivate the choice of a lower cut-off frequency for HPF2?

Ans: We used the same cut-off 280 Hz for both LPF and HPF1 (See Fig. 1 (b) and Fig. 5). The purposes of HPF2 in this article and FIL2 in Aart’s article are different. There is no HPF2 in Aart's article. FIL2 is a band-pass filter in Aart’s article to shape harmonic spectrum. We used HPF2 to simulate loudspeaker low-frequency bandwidth limitation problem.

Q2) As a result of the cut-off frequency difference reported in Q1, when reproducing your experiment (using the ATSR NLD), I tend to conclude that the bass enhancement mostly results from the gain (around +7 dB) caused by the NLD on the fundamental frequencies present in the band between 100 Hz and 280 Hz, and not much - if at all - from the generated harmonics. Did you come across the same observation?

Ans: I have explained the difference in filters and their purposes above. The main idea is that instead of shaping harmonic spectrum and removing the physical bass completely using FIL2, we let the physical bass components pass through the audio processing system together with generated harmonics by NLDs but we do not use any band-pass-filter (BPF) after NLD. HPF2 is instead used for simulating loudspeaker low frequency cut-off (See Fig. 1(b)). Not only ATSR, but also NLDs such as EXP2, FEXP1, NTANH and NSIG are good bass enhancers. See Table 14 and Fig. 11.

Q3) Could you also provide more details on filter HPF2? Does it have the same steep roll-off as LPF and HPF1?

Ans: For the HPF2, before the experiment 2 (i.e., bass intensity listening test), the wave files were high-passed filtered using Adobe Audition 2.0 > Effects > Scientific Filters. The cut-off is 100 Hz and the filter types and roll-off are not the same as LPF and HPF1. Note that HPF2 is not a part of bass enhancement system but is applied here to simulate low-frequency bandwidth limitation problem.

Ref:

E. Larsen and R. M. Aarts, "Reproducing low-pitched signals through small loudspeakers," J. Audio Eng. Soc., vol. 50, pp. 147-164, 2002.

AES Journal Forum: Comment by Christophe Macours on "Perceptually-Motivated Objective Grading of Nonlinear Processing in Virtual-Bass Systems"

Fri, 03 Feb 2012 09:38:54 -0700

Title: Perceptually-Motivated Objective Grading of Nonlinear Processing in Virtual-Bass Systems
JAES Volume 59 Issue 11 pp. 804-824; November 2011
Comment by: Christophe Macours

Many thanks for your answers. Please find below three additional questions.

Q1) In Aarts's article, HPF2 and LPF have the same cut-off frequency. This is a logical choice, since their intention was to evaluate the added value of the harmonics components on bass perception. In your article, HPF2 and LPF have cut-off frequencies of 100 Hz and 280 Hz respectively. What did motivate the choice of a lower cut-off frequency for HPF2?

Q2) As a result of the cut-off frequency difference reported in Q1, when reproducing your experiment (using the ATSR NLD), I tend to conclude that the bass enhancement mostly results from the gain (around +7 dB) caused by the NLD on the fundamental frequencies present in the band between 100 Hz and 280 Hz, and not much - if at all - from the generated harmonics. Did you come across the same observation?

Q3) Could you also provide more details on filter HPF2? Does it have the same steep roll-off as LPF and HPF1?

AES Journal Forum: Comment by Itai Neoran on "Improving the Magnitude Responses of Digital Filters for Loudspeaker Equalization"

Tue, 31 Jan 2012 09:35:56 -0700

Title: Improving the Magnitude Responses of Digital Filters for Loudspeaker Equalization
JAES Volume 58 Issue 12 pp. 1064-1082; December 2010
Comment by: Itai Neoran

After checking the Matlab code supplemented in this article, I found an error in the implementation of the MZTi, which is used as a reference in the article.

After fixing the error, I found, in the Matlab code example, that the MZTi method worked better then the article method

Comparing to the simple MZT method (Matched Z Transform), I found that the
article method, gave the same result as the MZT method

I checked it for the bell filter given in the Matlab example code, I can send the corrected Matlab code, for further investigation

AES Journal Forum: Comment by Nay Oo on "Perceptually-Motivated Objective Grading of Nonlinear Processing in Virtual-Bass Systems"

Sun, 29 Jan 2012 09:30:48 -0700

Title: Perceptually-Motivated Objective Grading of Nonlinear Processing in Virtual-Bass Systems
JAES Volume 59 Issue 11 pp. 804-824; November 2011
Comment by: Nay Oo

Thank you for your interest and questions.

Question 1: One question regarding to the bass-intensity listening test: the results in Table 11 show that the equalized track (EQ) scores marginally better than the reference (REF). Can you comment on this?

Answer 1: In the bass-intensity listening test, we use high-pass filter 2 (HPF2) (see Fig. 1). For HPF2, the cut-off is 100 Hz (see Section 4.2) to evaluate the virtual-bass effect generated by different NLDs. Equalization was performed off-line using Adobe Audition 2.0 software. The settings are as follows: Effects > Filters > Graphic Equalizer > 20 Bands> 12 dB for {-31, 44, 63, 88, 125, 180, 250} and 0 dB for the rest. The purpose of inclusion of EQ is to show that simply equalizing the low-frequencies does not work when low-frequencies cannot be reproduced due to the physical limitations of transducers (here we use HPF2 to simulate this effect). The listening test results in Table 11 shows the fact that is your question. EQ does not improve bass perception when some physical bass components are removed. Some NLDs due to its harmonic generation and missing fundamental effect can create virtual bass perception on the contrary and can enhance better bass intensity perception than simply equalization.

Question 2: Can the authors also provide more details on the exact filter specifications (LPF, HPF1, HPF2 and EQ) and the rationale behind those choices?

Answer 2: The rationale for including EQ in the experiment has been explained above. We followed Lasen and Aarts structure (Fig. 1 of [1]) to evaluate different NLDs on bass perception and distortion perception. One main difference is that we do not use band-pass filter (BPF) in both experiments but instead included HPF2 separately in the second experiment, bass intensity listening test. The rationale is to evaluate the distortion artifacts caused by these NLDs in the first experiment without including BPF. The filter specifications of LPF and HPF1 are described in Section 3.3 and 4.2 of our paper.

Reference:
[1] E. Larsen and R. M. Aarts, "Reproducing low-pitched signals through small loudspeakers," J. Audio Eng. Soc., vol. 50, pp. 147-164, 2002.