Fitting Procedures

A Solution to Challenges Faced by Hearing-impaired Musicians Performing on Loud Amplified Stages

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Advancements in IEM technology lead to improved onstage hearing for musicians | Hearing Review August 2014

For many years, the author—who is a performing musician, sound engineer, and audiologist—has been on a quest for a “personal sound system” that can help him hear well on a music stage featuring amplified instruments.  In this article, he reports on such a system built around a unique wide-band, high-fidelity in-ear-monitor (IEM) system that has binaural microphones imbedded in the earpieces, and that offers a means of inserting audio signal processing into the mix of sounds delivered to the user’s ears.

By Larry Revit, MA

The February 2009 edition of The Hearing Review discussed at length the many special challenges that hearing-impaired musicians encounter when performing on a loud amplified stage. The article1 I contributed for that edition described a “Personal Sound System” (PSS), which has been used, with limitations, to hear well during onstage performances—effective despite the author’s severe hearing loss.

Fig. 1

Figure 1. Original Personal Sound System, detailed in Revit (2009),1 mixes equalized signals in “stereo” from floor-standing stage microphones and the venue public address (PA) system, processes them with a stereo compressor/limiter, and delivers them to binaural in-ear monitor earphones via a second mixer/equalizer/earphone amplifier.

A block diagram of the original PSS is shown in Figure 1. With that system, a complement of floor-standing microphones transmit acoustic signals from three areas on the stage (left, center, and right), which are combined with a sound mix signal from the venue’s sound mixing board. These signals are “mixed-to-taste” by the user in stereo and are enhanced by signal-processing devices (eg, equalization [EQ] and compression/limiting) before being fed to binaural in-ear-monitor (IEM) earphones worn by the user. Among this system’s limitations are:

1) Three onstage microphones take up valuable “real estate” on stage;

2) The system is somewhat complicated and time-consuming to set up; and

3) It provides no solution for musician-to-musician communication (between songs).

A proposed “advanced PSS” in the 2009 article called for a modified version of the 3D Active Ambient™ (3DAA) IEM system from Sensaphonics.2,3 Paraphrasing from the 2009 article: The 3D Active Ambient IEM System is designed not only to deliver high-fidelity signals directly from sound systems via custom-fitted, binaural, sound-isolating insert earpieces, but it is the only IEM system that provides high-fidelity, spatially accurate ambient sound via binaural, field-corrected microphones imbedded in the full-concha earpieces (Figure 2a). The earpieces provide up to 37 dB of acoustic sound isolation, and the belt-pack circuitry offers selectable output limiting, to protect users from overly loud sounds. Because the left and right output limiters are electrically linked, accurate lateral sound localization is maintained even when output limiting is active.

The binaural ambient microphones of the 3DAA system address at least the first and third of the limitations of the original PSS, often eliminating the need for stage microphones, and providing a means of communication with other musicians on stage. The necessary modification to the original 3DAA system would include a means of inserting signal-processing devices to accommodate the auditory needs of the hearing-impaired listener. However, at that time, there was no protocol to access the ambient microphone signal path for such customized processing.

Figure 2a-b. 2A: 3DAA IEM earpiece in situ with built-in ambient microphone. 2B) Sensaphonics 3D-AARO in-ear-monitor (IEM) belt pack and earpieces, depicted with “microphone outputs” (new) and “monitor input” ports. Operating mode switch is set to “performance” position. Internal ambient gain switch (not shown) set to “off.” (Photos provided by Sensaphonics.)

Figure 2a-b. 2A: 3DAA IEM earpiece in situ with built-in ambient microphone. 2B) Sensaphonics 3D-AARO in-ear-monitor (IEM) belt pack and earpieces, depicted with “microphone outputs” (new) and “monitor input” ports. Operating mode switch is set to “performance” position. Internal ambient gain switch (not shown) set to “off.” (Photos provided by Sensaphonics.)

Since the time of the 2009 article, Sensaphonics has introduced a new model, the 3D-AARO (Figure 2b), which adds a user-accessible, 2-channel output from the ambient microphone signals. Normally intended for making live binaural recordings, the microphone outputs port also enables the insertion of external signal processing between it and the monitor input port.

Fig. 3

Figure 3. Block diagram of the PSS-3D system. All signals are two-channel, left and right. [Note: The “Mode” switch on the belt pack (see Figure 2B) is set to the position used for normal performance. An internal, multi-position 3D ambient gain switch (not shown) is set to the off position.] The superscript numbers correspond to the numbered descriptions in the text.

This article introduces a new version of the PSS—built around the 3D-AARO—the “Personal Sound System-3D” (PSS-3D, Figure 3). The author has used the PSS-3D on stage in small venues on several occasions, with great success, playing both electric guitar and electric bass. The author enthusiastically reports that using the PSS-3D system on stage while performing music with amplified instruments and a PA system has enabled the author (with severe hearing loss) to hear an amplified and complete balanced sound without audible distortion, while enabling musician-to-musician communication between songs. He therefore could perform amplified music comfortably and effectively, despite his severe hearing loss.

System Components

Essentially, the PSS–3D works much like a very-high-fidelity master binaural hearing instrument that is capable of mixing and processing multiple sound sources. The user wears custom-made, soft silicone, full-concha earpieces that contain microphone transducers, preamps, and receiver transducers. The earpieces connect to a 9V-battery-powered belt pack (Figure 2b).

The binaural microphone signals from the belt pack feed a mixer that adds signals from the house or monitor sound system and, optionally, floor-standing area microphones on the stage. Each sound source can be equalized separately. The mix of signals feeds a multifunction, user-programmable digital signal processor (DSP) before returning to the belt pack and then the earpieces, via a second mixer that provides final EQ and gain adjustments.

Details of the system components are described here, and each numbered section below corresponds to the superscript-numbered elements in Figure 3.

1) Binaural ambient microphone signals from the earpieces. Signals from the microphones and their preamps in the IEM earpieces connect to the 3D-AARO belt pack via a lightweight, flexible but sturdy, strain-relieved cable. This cable also provides operating power to the microphones and preamps in the earpieces.

The microphones used in the 3D-AARO, along with associated circuit components, are capable of operating with inputs as high as 140 dB SPL without distorting. Of note, although this may appear to be “overkill,” it is important to understand that, for drummers (and others), the peak ear level SPL during performance may reach 140 dB SPL.3

Fig. 4

Figure 4. PSS-3D outboard equipment array.

The output level in the user’s ear, of course, must be, and is, controlled for safety (especially important with added gain [see item #8 below]). In a smaller venue, binaural ambient signals with appropriate enhancement are often all that is required for an excellent listening experience. The binaural ambient part of the PSS-3D system performs much like an ultra-flexible, ultra-hi-fidelity master hearing instrument—albeit one that is connected by cables to the outboard equipment of Figure 4.

2a) Microphone outputs port. During “normal use” conditions, the ambient microphones and internal circuitry of the 3D-AARO provide a maximum of 0 dB (unity) insertion gain, tuned for transparent ambient communication among normal-hearing users. In the current application, the addition of gain and signal processing to the ambient signals becomes possible via the “microphone outputs” port on the 3D-AARO belt pack. The microphone output port uses a stereo mini-jack (3.5 mm), as is commonly used with many small audio products. It lets the user access the ambient microphone signals by connecting a stereo cable between the belt pack and two inputs of the pre-DSP mixer (see item #3 below).

2b) House PA or monitor mix. Most PA systems provide an auxiliary output port, allowing the PSS-3D user to access a mix of signals from the PA system by connecting an audio cable from the PA system to a third (and fourth, in a stereo feed) input of the pre-DSP Mixer (see item #3 below).

In small venues, the house PA and/or monitor mixes that are normally directed to the audience area or to the stage, respectively, provide amplification for acoustic (unamplified) elements of an onstage ensemble (eg, vocals, acoustic guitars, horns, etc). Electric instruments (such as electric guitars and basses) generally are amplified by onstage instrument amplifiers, and typically are not part of the PA or monitor mixes in small venues.

In large venues, typically all instruments and vocals are fed to the PA and monitor sound boards, and are mixed and processed by sound engineers in the house and onstage.

2c) Optional stage microphones. An essential sound source with the original PSS, the three area microphones on stage now become “as needed” with the PSS-3D. Their function is at least partially replaced by the built-in, in-ear binaural microphones worn by the user. On small stages, where all the instrument amplifiers are nearby, there may be no need for additional area microphones. On large spread-out stages, floor-standing microphones may be needed (eg, stage left, center, and right) for enhanced pickup of distant amplifiers and instruments not fed to the PA system. These microphones would be connected, along with the ambient microphone and PA signals, to separate channels of the Pre-DSP mixer (see item #3).

3) Pre-DSP mixer. The pre-DSP mixer fulfills four purposes:

  • It provides supplemental preamplification of the binaural ambient microphone signals for matching the mic-level signals to the line-level input range of the DSP unit. The binaural microphone channels are panned left and right, while the PA/monitor-mix signal, if mono, is panned center.
  • It allows the mixing and balancing of the house or monitor feed (see #2b above) with the binaural signals, before DSP.
  • It allows pre-DSP tonal adjustments (EQ) of each sound source, independently.
  • It delivers an electrically balanced, line-level signal to the DSP inputs. A master stereo gain control adjusts the mixer output to accommodate the operating range of the DSP unit (see #4 below).

4) Digital Signal Processor (DSP). Shown in Figure 4, the Behringer DEQ2496 is a good example of a relatively inexpensive 2-channel digital signal processor that provides several very useful functions, including many that are found in programmable hearing aids, and then some. The functions of the DEQ2496 include (but are not limited to):

Fig. 5

Figure 5. DSP Graphic Equalizer. Used with the current “modified” application of the 3D-AARO to defeat the internal monitor EQ, thus restoring the transparent tonal character of the internal signal path of the ambient microphones experienced in the “normal” operation of the 3D-AARO. When appropriate, the high-frequency boost of 2 dB at 10 kHz could extend to 5 dB at 20 kHz, but no extended boost was used in these trials, as the user’s residual hearing (ie, the author’s hearing) does not extend to that range.

 (see Figure 5), one of two broadband equalization devices available in the DEQ2496 that are capable of extensive frequency shaping. In normal live-music performance uses (ie, no external DSP path), the 3DAA system has separate internal equalization circuits for ambient and monitor signals. In the PSS-3D configuration described here, the ambient signals pass through both internal equalizers.

The best starting point for overall frequency shaping is to make use of only the ambient EQ, which provides a transparent tonal character to the ambient sound, as is the case for the “normal use” condition of the 3DAA. Therefore, the graphic EQ settings shown in Figure 5 are used to defeat the internal monitor EQ (R. Schulein and S. Julstrom, personal communication), before adding other tonal adjustments elsewhere in the signal path, such as adjustments that compensate for the user’s hearing loss. The user’s final choice of equalized sound quality is entirely determined by the user.

Figure 6. DSP Parametric Equalizer. In this case, set for a broad, shelving high-frequency boost, with notch filters set to reduce feedback at two frequencies.

Figure 6. DSP Parametric Equalizer. In this case, set for a broad, shelving high-frequency boost, with notch filters set to reduce feedback at two frequencies.

Parametric Equalization or PEQ (Figure 6). Allows definition and control of up to 5 separate frequency bands and provides independent adjustment of EQ bandwidth for each band. This example used a broad high-frequency boost, such as to compensate for comparatively poorer hearing at high frequencies, and two narrow notches at frequencies that were prone to feeding back with an earlier version of earpieces the author had been trying.

A later, better-fitting set of earpieces allowed elimination of the anti-feedback notch attenuators. The PEQ was not used at all in the final trial, as sufficient high-frequency boost was obtained with the EQs of the pre- and post-DSP mixers (see Figure 4).

Fig. 7

Figure 7. DSP Compressor. Set, in this case, to provide gentle, broadband, wide-dynamic-range compression. In this example, the gain was set to -8.5 dB to help keep the DSP output level within a convenient operating range; the threshold (kneepoint) was set low, with a gentle compression ratio (1.4:1); the attack was set to a fast 2.3 msec; the knee shape was set for a sharp break (as opposed to curving); and the release time was moderate at 304 msec.

Dynamic-range Compression  or DYN (Figure 7). The DYN feature offers fully adjustable control of compression parameters:

  • Gain (not shown in Figure 7);
  • Threshold or kneepoint (not shown);
  • Knee shape (sharp to gradual);
  • Compression ratio (not shown);
  • Attack time; and
  • Release time.

Peak Limiting. This feature controls maximum output without clipping (Figure 8). This fast-acting peak limiter can be used to supplement the slower-acting internal output limiting built into the 3D-AARO circuitry (see item #8, below). For the current onstage trials, it was set by ear to allow a maximum audible dynamic range without exceeding comfort for high peak levels.

RevitRevised_Fig._9

Figure 9. DSP Dynamic Equalizer. Set for reduced gain below ~500 Hz for high-amplitude signals.

Dynamic Equalization (DEQ). As shown in Figure 9, this feature allows band-specific automatic gain control, in low-, middle-, or high-frequency bands. This example was set for reduced low-frequency gain at high levels (commonly called “BILL,” for “bass increase at low levels”). The intended purpose was this: In loud, “bass-heavy” environments, low-frequency sound passing into the ear canals through or around the earpieces can artificially enhance the relative bass content of the perceived sound mix. BILL processing can potentially reduce low-frequency gain for increased input levels, and therefore reduce the effect of this artifact when the ambient sound reaches a chosen threshold.

Memory Storage and Recall (not shown). Allows storage of several setups for differing onstage conditions.

5) Post-DSP mixer. This small mixer provides overall gain, EQ, and easy final balancing of left and right signals before returning the signal to the 3D unit via unbalanced lines.

6) Monitor input port. This is the signal received by the 3D belt-pack unit before delivery to the IEM earphones via its internal limiter.

7) IEM earpiece receivers. Sensaphonics offers single- and dual-receiver earpiece models, which are capable of outputting 124 or 130 dB SPL, respectively, in an average ear canal (measured at 500 Hz). Ideally, the custom-made, soft silicone earpieces must be made from near-flawless earmold impressions; otherwise, feedback may be a problem at high frequencies, especially when considerable high-frequency gain is needed. Sensaphonics has a nationwide network of specially skilled “Golden Circle” audiologists who offer high quality impressions (http://www.sensaphonics.com/sensaphonics-audiologist-network).

Fig. 8

Figure 8. DSP Limiter. In “normal” unity-gain ambient operation, the 3D-AARO provides an optional internal limiter set to 105 dB SPL, with a comparatively slow attack to pass natural peaks while controlling long-term output levels. In the current application, with added gain, it was determined that a supplemental, fast-acting peak limiter was useful for controlling the level of transient peaks.

8) Built-in output limiter (AGC-O). This feature limits maximum output at 105 dBA SPL. Attack time is slow enough to let musical peaks pass naturally. In the current application—which adds remedial high-frequency gain to the delivered sound—a supplementary peak limiter (part of the DSP, see above and Figure 8) was used to reduce transient peak levels. The built-in limiter can be switched off when desired.

Caveats and Comments

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Table 1. Approximate cost of the Personal Sound System-3D proposed here.

Price. The PSS-3D system is somewhat expensive, depending on the importance to you of good onstage hearing. Currently, the PSS-3D system described here will cost about $3,000 (see Table 1).

Setup. Setting up the PSS-3D system will add about 10 minutes to your setup time. Currently, you’ll have to remain tethered to the external processing equipment (I use 10-ft cables). This is certainly less convenient than popping in a couple of hearing aids. However, considering what you get for your trouble, it’s arguably worth the extra effort.

Pre- vs post-DSP equalization. Pre-DSP equalization lets you control the spectrum of the signal that drives the DSP devices—similar to the way a “side-chain” compressor input would allow tuning of the control signal.

For example, when I am playing electric bass, I find it helpful to roll-off the bass frequencies a bit, before the DSP, because from where I stand onstage (near the bass amp), the bass is predominant in the ambient sound and would otherwise exert a disproportionate amount of control of the DSP. If needed, restorative bass boost can be added after the DSP, using the EQ of the post-DSP mixer.

High frequencies are another story. Most of the high-frequency boost I use (about 15+ dB) is done by the easily accessible post-DSP mixer. That choice provides linear high-frequency gain; I find that unprocessed (post-DSP) supplemental high-frequency gain results in better high-frequency clarity.

Importance of full audio band frequency response. The frequency-response range of this system is 20 Hz to 16 kHz. To the author’s knowledge, no hearing aid can match that range. Indeed, it would be somewhat impractical to use a significant portion of the power from the 1.4-V battery of a hearing aid to process frequencies that are rarely used, in general, and never used for speech. There are currently hearing aids that extend to about 10 kHz (or more) at the high-frequency end, but still roll off below 150 or 200 Hz.

The low-frequency end of the tonal spectrum is important for musical high-fidelity. For example, the fundamental frequency of the lowest note of a double bass is about 41 Hz; the low B of a 5-string electric bass is about 31 Hz; a standard piano’s lowest pitch fundamental is at 27.5 Hz. Also, tonal and non-periodic elements of at least a handful of other instruments reach below 60 Hz.4

Arguably, music can sound more balanced and natural when all its elements are audible, without audible distortion. These qualities can be important to the listening experience of a performing musician, and therefore can be important to the musician’s performance.

Different hearing losses mean different needs. Musicians with mild-to-moderate hearing loss may require less in the way of processing than provided by the equipment described here. For a moderate hearing loss, the DSP device may be amply replaced by a simple compressor/limiter, as was used with the original PSS (Figure 1), while sufficient equalization may be provided by the mixers. For mild hearing losses, even compression and supplemental limiting may be unnecessary, and the equalization provided by a single mixer may suffice. Editor’s note: See Marshall Chasin’s article on page 26 of this special edition for more discussion on this topic.

Earpiece seal is paramount. The importance of “earpiece seal” cannot be overemphasized, especially when severe hearing losses call for substantial high-frequency gain. To minimize the chance for feedback in high-gain situations, the author recommends having a highly skilled and experienced hearing care professional make the impressions for the soft silicone earpieces. In some cases, the best seal may be obtained when the smallest flat-surface dimension of a foam bite block holds the mouth slightly open during the impression-taking process, although Sensaphonics reports a good seal is usually obtained without using a bite block (Michael Santucci, personal communication).

The importance of good hearing with reduced overall sound levels. Case in point: Upon completion of the last trial of the PSS-3D system, I turned off the system and removed the earpieces while the rest of the band then resumed playing. To my surprise, the ambient sound onstage was considerably louder to me when I removed the earpieces. In other words, with the PSS-3D, I had chosen to use listening levels for which musical intelligibility and performance were comfortable and clear, yet those levels (thanks to the seal of the earpieces) turned out to be lower in loudness than were the ambient onstage levels.

I can also report that the entire time I was playing onstage, I was smiling—experiencing comfort and good hearing—released from the pressure of having to “try” to hear well while performing.

A Wish List

Wireless. A wireless version of the PSS-3D system would be welcomed. It would require four channels to transmit and receive, for sending the ambient microphone signals from the belt pack to the PSS mixer, and then sending the processed signals back to the belt pack (left and right, in each case).

Self-contained system. A self-contained DSP unit (such as could be built into the IEM belt back) would add considerable convenience.

Generic earpieces. The availability of earpieces that seal the ear with generic tips (such as made of compressible closed-cell foam) would help to bring down the cost of a PSS-3D system, as well as allowing sound-system providers to offer IEM systems (including the PSS-3D) for temporary use to band members who don’t have their own units.

Conclusion

The Personal Sound System-3D represents an effective solution for musicians with hearing loss who seek an excellent onstage sound system. The author’s severe sensorineural hearing impairment can be presumed to present a near-worst-case scenario for any such system to serve well. The enthusiasm he reports for how well the system works for him suggests that the PSS-3D, or distillations of it, will be useful for a wide range of hearing loss configurations. With the versatile, professional-audio-quality components of the PSS-3D, musicians with hearing loss should achieve good hearing while performing on stage.

Acknowledgements

revit author boxThe author conceived, designed, and field-tested the PSS-3D system. Sensaphonics supported the evaluation of the PSS-3D system by providing the test 3D-AARO belt pack and custom, dual-transducer earpieces, as well as providing substantial consultation regarding details of the workings of the 3D-AARO system. Special thanks are due to Robert Schulein, MSEE, for his support throughout this project.

References

1. Revit LJ. What’s so special about music? Hearing Review. 2009;16(2):12-19.

2. Santucci M. Please welcome onstage…personal in-the-ear monitoring. Hearing Review. 2006;13(3):60-67.

3. Schulein B, Julstrom S. Sensaphonics 3D active ambient IEM system. Live Sound International. 2007;16(1):72-75.

4. Everest AF, Pohlmann KC. Master Handbook of Acoustics. 5th ed. Columbus, Ohio: McGraw-Hill;  2009:81.

Original citation for this article: Revit L. A solution to challenges faced by hearing-impaired musicians performing on loud amplified stages. Hearing Review. 2014;21(8):34-38.