Home Audio Fidelity - Room Shaper Review

Home Audio Fidelity’s “Room Shaper” is an innovative digital signal processing (DSP) software product designed to even out low frequency room modes in your listening environment.

Low frequency room modes that have uneven decay times can have a negative impact on one’s listening experience. This can be heard when certain bass notes (i.e. frequencies) take longer to decay than other bass notes. Often called room resonances.

In this review, I show how to setup and configure Room Shaper, objectively compare the before and after decay times and provide a subjective listening experience using music to hear what was removed from the room. I must say upfront that I am impressed with this innovative DSP software product that lives up to its claim of “as if the room disappeared.”

Preamble

Some technical info to help folks understand what problem this product is trying to solve. It involves some physics and how a room can impact the sound quality, especially the low frequency response of loudspeakers in a room. If you prefer, one can skip to the objective measurements or subjective listening sections.

Typical sized living rooms and home theaters are dominated by modal resonances in the low frequency region. Unless one has acoustically designed and constructed a room using proper room ratio’s to distribute the room modes evenly, virtually every listening room has uneven bass response. From the linked article:

The key phrase is, “it is the excessively long sound decays of the modes that make them stand out and more audible.” It is akin to the resonance one hears when blowing air across a Coke bottle for example, except at a much lower frequency. Technically, one can use Digital Room Correction (DRC) products to equalize the minimum phase response at the listening position. Further, the DRC products I have reviewed provide time domain correction by time aligning speaker drivers and applying excess phase correction.

Room Shaper’s algorithm is different than DRC as it targets low frequency decay times that are longer than others. By using time domain correction, shortening the long decay frequencies to be the same as adjacent frequencies results in an even decay time over frequency in the low end. Much like changing the shape of ones room to a preferred room ratio. Room Shaper also assists in taking out the “boxy” sound of a room up to 600 Hz. What does “boxy” sound like? You will be able to hear it on the recording I made later in the review.

It should be noted that Room Shaper does not produce a digital FIR filter like DRC products where filtering is a linear transformation applied continuously to the whole signal. Room Shaper is based on events detection and modifications of only some portions of the input signal.

Room Shaper can complement any DRC product as it is targeting a different issue (i.e. reducing low frequency decay time) than DRC addresses (i.e. frequency and time domain correction). In my case, I use Audiolense and Acourate. Of course, one can simply use Room Shaper as a standalone VST plugin as DRC is not a requirement. I am using JRiver MC25 as the host for the plugin.

To further illustrate the point, our listening rooms have a transition frequency where room resonances dominate the frequency response and the speakers are no longer in control. Here is a graph similar to the one linked above but showing the transition or Schroeder frequency:

From Floyd Toole’s Audio Science article.

It is calculated based on one’s room dimensions where room resonances take control of the low frequency response regardless of the speakers being used. I like this Room Mode calculator as you can move the cursor along the frequency scale and it will output a tone at that frequency. If your computer is hooked up to your speakers (careful with the volume!), you can hear the resonances in your room by hovering the cursor over the modes in the graph. It is an ear opening experience and great for training ones ears to know what to listen for.

Good digital room correction systems can even out the low frequency response at multiple listening positions below a room’s transition frequency. Unless one has an acoustically designed room, with good room ratios, DRC is almost mandatory as one can’t (easily) change the physical dimensions of the room.

What about bass traps? While bass traps do absorb low frequencies the issue is below Schroeder frequency one needs to literally stuff the room with bass traps in order to have any significant absorbent impact below 100 Hz. The downside is, aside from the dollars spent and the number of traps in one’s room, bass traps are not “surgical” in nature and also absorb frequencies above the affected region (i.e. above the rooms transition frequency) to the point of having a near anechoic chamber for a range of frequencies. Usually the upper bass and lower mids are too absorbed. Having worked in some really absorbent rooms like studio control rooms and critical listening environments in the past, too much absorption really sucks the life out of the music. There are a few industry guidelines that specify how lively a listening room should be based on room size for listening conditions for the assessment of sound program material and methods for the subjective assessment of small impairments in audio systems.

OK enough tech talk. Hopefully this illustrates the problem well enough to understand how Room Shaper solves a particular acoustic problem that the majority of us suffer from. From Floyd Toole’s research, bass subjectively accounts for 30% of how we judge speakers sound quality.

Setup, Measurement and Configuration

After downloading Room Shaper, the plugin can be installed in any software program that supports VST plugins. I am going to install it in JRiver Media Center 25.

While one can place the VST anywhere on the hard drive, I copied Room Shaper to C:\Program Files\Steinberg\VstPlugins.

In JRiver, click on Tools and select Options. In Settings, select DSP and output format. At the bottom left, click on Manage Plugin-ins. Navigate to the location where Room Shaper VST was copied to. Here are a few screen shots from JRiver to help with the procedure:

Once installed, it should look like this:

Room Shaper should be moved up as far as possible in the DSP ordered list. One can simply drag Room Shaper to move it up the list so that after the default JRiver processing, Room Shaper is next to process. We also want Room Shaper to process the full range signal, so click on Options to the right of the plugin and select, “Process independently of internal volume:”

Since I have been using Room Shaper for a while, we can see mine is already configured. Let’s reconfigure so folks can see the steps of what needs to be done.

A calibrated measurement microphone, like the UMIK-1 is required as we are going to take left and right speaker measurements using the acoustic measurement software package REW with the measurement mic at the listening position, at ear height, where we would typically listen.

There are several guides for taking acoustic measurements. In this article, I wrote a simple section on “set up to take measurements” (scroll down a bit) is a quick primer. REW also has a few guides, including using UMIK-1 for folks that are new to REW.

From Home Audio Fidelity’s manual:

This procedure describes how to perform room impulse measurements by using REW and an external player to play the measurement (sweep) signal. By using this procedure, it is possible to include a digital correction while performing the room measurement:

Download the sweep signals

Add them to your favorite player

Activate or not digital correction in your player (convolution for instance)

Start REW and configure your microphone

Select "Measure" option and configure the panel with following options SPL start Freq: 20 Hz end freq: 20 000 Hz length: 256k "use acoustic timing reference" "wait for timing reference" the other parameters can be left as default



Press "Start measuring": REW will wait for a sync signal that is embedded in the downloaded sweep signal. As REW will play its own test signal when you press "Start measuring", be sure REW’s own test signal is not audible. The easiest way is to choose the internal sound card of your computer as an output device (via REW Preferences menu) and put your computer volume at zero.

Play the left channel sweep signal (_L_refL) from your player and check that the level measured by REW is in the acceptable range (make sure to stop the player after the file plays).

Rename the measurement (Left for instance) and export it as a WAV file. See screen shot below.

Repeat the procedure for the right channel by playing the right sweep signal ( _R_refR)

Rename the measurement (Right for instance) and export it as a WAV file

After you have measured both channels, the REW screen should look similar to mine:

The two measurements are now ready to be exported. To Export the impulse responses:

The following dialog appears:

Use the same settings you see above. Export both left and right channels to a project folder you can create on your hard drive at whatever location to contain the impulse responses.

In my case, since I loaded Room Shaper VST into JRiver, this is where I will configure the plugin by importing the exported room impulses by clicking on “IR Left” button on Room Shaper. A file dialog will open and select your left impulse response:

IR Left is now loaded. Import IR Right. Then click on Configure:

The processing may take a minute or so. Once completed, we are ready to listen to some music. But first, let’s take some objective measurements so we can understand the impact of Room Shaper.

Objective Measurements

This is a unique DSP software product and I was unsure of what would be the best way to objectively measure the impact. I did use REW’s waterfall graph and it indeed shows a measureable difference in reducing certain frequencies, but does not really relate the musical impact of what the processing is doing in the time domain.

Another approach is comparing music waveforms over time. Audibly, it allows one to hear the impact using music. It is simple procedure to perform as one can record the digital output of a music player, once with Room Shaper in the signal path and another recording without. Here I am using JRiver to play music and using Audacity to record the digital output:

I recorded some samples from Madonna’s Ray of Light album, “The Power of Good-Bye” as an example since it has sustained bass notes that allows one to hear what is being removed from the room. I recorded about 90 seconds and is used on the basis of fair use for the purpose of evaluation and research. I am not doing this for financial gain. Please delete these music samples once you are done with the evaluation. Note my Lynx Hilo uses a multi-client ASIO driver, which allows me to use multiple client applications so one app can play music and the other recording the output.

The next step is to load the two recorded stereo tracks into one’s favorite audio editor to perform some basic digital audio editing. The idea is to line up each stereo track so that they are in perfect sync. Then invert one stereo track and mix down all tracks to a summed stereo track. Whatever is left over, is what is being removed by Room Shaper. This procedure is often referred to as differencing. One can review the detailed procedure in this article if you are interested.

Here is the difference file so you can hear what is being removed in my room. The level has been normalized so you don’t have to turn it up super loud to hear. Of course, in the room, it is at a lower level relative to the direct sound as can be seen later with the dB scale spectrograms:

Madonna delta Room Shaper (15 MB wav)

Madonna delta Room Shaper (13 MB zip)

Here is the frequency spectrum of the difference file:

Only frequencies below 600 Hz are being processed (i.e. the ones with the long decay times) and is reduced in level at the output. One can see the low frequency peaks that are being removed, along with the “boxy” room peaks between 300 to 500 Hz.

It helps to listen over headphones (i.e. to remove your room) and ideally one has headphones that go deep enough in bass response to hear what is being removed from the room. If you listen closely you can hear consistent bass resonances being removed and on certain bass notes quite a bit of resonance is being removed, especially the longer the bass note sustains, the more is removed. Another aspect one can hear is the “boxy” sound of the room being removed. Remember, what you are listening to are room resonances and no direct sound. It may take a moment or two to tune into what one is hearing.

To help visualize this, here are a couple of charts that illustrate the acoustic issue and what exactly is being reduced in level.

The top chart shows the spectrogram (i.e. decay time) of my room (in milliseconds) over frequency and the dB level is in color. The bottom chart is the corresponding frequency response measured at the listening position. Left speaker:

Right speaker:

Even with a smooth frequency response at the listening position, one can see the long decay times in my room below 100 Hz in the spectrograms. If you look closely, you can see there is longer decay times in the 300 to 500 Hz range as well. That frequency range is what gives a room a “boxy” sound quality to it. It is the combination of room ratios and how lively the room is, which in my case is pretty lively as there is little absorption in my room. Other than a couple of bass traps, a half dozen broadband absorbers, quiet curtains, and a throw carpet (with double underlay) between the speakers and leather couch, everything else is drywall, glass and hardwood floor which dominates my room.

So what does Room Shaper do to the long decay times below 100 Hz? Here is the left channel spectrogram where on top is the room and the bottom is with Room Shaper on. I have put a red square around the area to focus on when you compare the top to bottom:

The red block encompasses frequencies from 10 Hz to 1 kHz and time frame from 250 to 500ms. Note in the top diagram that resonance at around 70 Hz is a solid greenish blue color (i.e. about -20 dB in level) and does not diminish in level, well past 500ms. In the bottom graph we can see that has been reduced to be in line with adjacent frequencies plus all the way down to 10 Hz has been significantly reduced (i.e. -20 dB of reduction).

In the top room spectrogram, you can also see several solid darker blue lines from over 100 Hz to about 300 Hz stretching from 250 to past 500ms. Again, in the bottom pic using Room Shaper, we can see that area has been reduced in level to be at similar levels to adjacent frequencies that are not long decay times.

The right channel is more of the same:

If you look at 10 Hz in the top spectrogram and out to just before 400ms, one can see a pretty high level resonance (about -15 dB in level at 400ms with a twinge of green). In the Room Shaper bottom chart, we can see that has been reduced by about -20 dB, so perceptually to ones ears, about one quarter as loud as it once was, at 10 Hz! I know of no other technology that can do this.

Now that we have some objective proof that Room Shaper’s algorithm processing can be measured and audibly heard, what does it subjectively sound like on a variety of music?

Subjective Listening

The measurements and difference file above is with Room Shaper’s logarithmic Effect and Sense control set to maximum (i.e. default position). To my ears, it takes a little too much of the room resonances out of my living room. In my room the music sounds overly damped in the low end with the Effect/Sense controls set to maximum. With careful listening (at reference level 77 to 83 dB SPL) I found a balance of about halfway or 50% rotation of the Effect and Sense controls to provide the best balance. While adjusting the Effect control, I am listening for solid low frequency bass that did not activate the room, yet not sound overdamped. Then I adjusted the Sense control threshold to a level between being on all the time and just the peaks, while listening to music. Like the Effect control, there appears to be a sweet spot where the bass and lower mids sound crystal clear.

Note there can be up to 1.5 seconds of delay between adjusting the Effect/Sense controls before hearing a change, including the bypass control. Remember this DSP software product works in the time domain.

While I have posted this before, I use this list of tunes to evaluate gear as it has some decent dynamic range and I have heard most of this music over and over again for a dozen or so years on a wide range of audio gear. Sure, it is Dad rock 😉

To get into specific examples with some not from the list above:

Excellent pop recording that is well produced/mixed. On the Power of Good-Bye, there are sustained low frequency bass notes that on my dual Rythmik 18” subs can pressurize my living room. With Room Shaper the bass notes are clear, articulate and deep with no overhang or room resonance. It is interesting to play with the effect control while listening in real time. It is almost like a focus control where the bass becomes the clearest sounding. Too little effect and the bass sounds resonant, too much sounds overdamped and losing bass. It takes a bit of time to train one’s ears to know what to listen for. The Room Mode calculator I mentioned in the preamble can assist in training ones ears.

Remember this has little impact on the direct sound and is targeting beyond 250ms of room decay. As mentioned before, it is like blowing across a Coke bottle resonance where a particular tone or frequency takes a lot longer to decay than adjacent frequencies. This is what to listen for, but at low frequencies. And in ones listening environment, it is not just one frequency, but several frequencies (i.e. room modes), and each can potentially have its own decay time.

Another difference I hear is the synth lower mids are much clearer. If you listen to the difference recording, one can hear a lower mid “peaky” resonant sound in my room. With that removed, one can hear the nice stereo effect of the keyboards with proper tone. The clarity is outstanding.

One of my all-time favorite performances/recordings that I find really enjoyable to listen to is SRV’s Tin Pan Alley. I never get tired of hearing it and the fantastic use of dynamic range driven by Stevie and Double Trouble. The emotion of this blues tune goes up and down in volume over the course of the song to make one feel like you are there with the band, live at the venue. It is a crying shame there are so few “modern” rock, blues, pop, alt, recordings with this type of dynamic range that moves with the mood of the music. Unfortunately, extreme dynamic range compression has all but killed the musical life out of most recordings.

In my room, Tin Pan Alley without Room Shaper has several bass guitar notes that resonate in my room. Switching in Room Shaper, not only tames those resonant bass notes, but provides a clearer picture of the lower mids, so that SRV’s guitar work sounds more articulate, as does the lower register of his voice in my room. I also notice the tone of the drums are clearer sounding without the room resonance masking the tone of the drums decay, especially the toms. I used this song to dial in Room Shaper’s Effect control. There is a sweet spot where the bottom end sounds tuned in, clear sounding with no overhang. It is like a focus control. Too little sounds muddy, too much sounds overdamped. I must say SRV has never sounded better on my system.

As a guitar player, I am a fan of Eric Clapton. Learned to play some of his tunes. I like this particular live version of Badge. Excellent “live” recording. The bass guitar is turned up in the mix as is the kick drum and drums overall. Turning the volume up, the bass really pounds and one can feel the punch of the kick drum. For me, that’s the dream. I want to feel like I am at the concert or club listening to whatever band I feel like at the time with the punch and kick of a good live sound system. With dual 18” subs with 1800 watts and 4 x 15” woofers with 1000 watts covering 6 Hz to 630 Hz, I am getting there ☺

This song has great energy and just plain rocks out at the end with the bass thumping and drums pounding. You can feel the energy from the band and audience. For a stereo illusion, it is pretty convincing to close ones eyes and imagine being there. Lots of fun! And if you are a Cream fan, I can also recommend the Live at Royal Albert Hall 2005 video as well. Excellent recording/mix with a sense of being there.

Looking at my listening notes, the dropping bass drum sound on Patricia Barber’s Regular Pleasures is a real treat as not only the impact of the drum sounds sharper, more impactful, it is being able to hear the decay of the drum sound clearer with Room Shaper on. Dire Straits, Six Blade Knife has the bass guitar level up in the mix and always sounded a bit “tubby” in my room, even with a flat frequency response in the low end. Room Shaper cleaned that right up being able to clearly distinguish between each note on the bass guitar with no room resonances.

Stewart Copeland’s drums on Murder by Numbers by the Police sound like I am right in the drum room standing in front of the drums. The crack of the snare and punch of the kick drum sound incredibly tight and carrying through Stewart’s trademark articulation on each hit. The outro has the drum group cranked right up in the mix and bashes away. Love it. “Chaiyyaa Chaiyyaa” by Sukhwinder Singh & Sapna Awasthi has a variety of stereo effects that come through more clearly as does the drums and the drop bass as one goes further in the tune. Makes my wood house shake on its foundation, but in line with the rest of the decay times. Impressive!

I could go on, but I think that by now one can see a consistent theme. Much clearer, non-resonant sounding bass and removal of “boxy” room sound. It becomes a new listening experience that was once only reserved for acoustically designed and constructed critical listening environments. Quite the innovation.

Conclusion

Indeed a new listening experience with Thierry’s Room Shaper product. Room resonances are real and measureable and to my ears, I can hear the difference readily with the addition of Room Shaper in the signal path in a positive way. A quick AB test with my lovely assistant switching Room Shaper on and off with my eyes closed, I could pick Room Shaper out 10/10 times. Once you hear resonant free low frequency sound reproduction and the “boxiness” of one’s room removed, it is hard to go back ☺

I am simply amazed that this can be accomplished using a software DSP VST plugin (Room Shaper plugin: 129€, 69€ for HAF service customers). Usually one needs to spend a small fortune on an acoustically designed and constructed critical listening environment. I say this as the last time I heard non-resonant low frequencies and an unboxy room was in an LEDE studio control room in Vancouver, Canada many years ago.

Listening to the effect is like the room has disappeared. Or simply, the decay times across lower mid and bass frequencies are now similar in length. I find I can hear more into the music and less of my room. It is an audible, but subtle positive effect of making the low frequency sound clearer with no resonances and the added bonus of taking out the lower mid “boxy” sound of the room. One can hear the “boxy” sound on the keyboard synthesizers on the Madonna difference file. Very peaky buildup of lower mid sound being removed from my room. Closing my eyes, the sound field image is the size of the front wall. Not only do my fugly fridge size industrial speakers disappear (they did before with DRC), but the room is gone as well. No muddy resonant bass sound or room boxiness. Again, I am impressed the more I listen. Works a treat.

A couple of operational notes. The plugin crashed (and JRiver exited) once while listening to music over an extended period (several hours). While the plugin works with video in JRiver, unlike convolution where the delay is known, there is no delay compensation with Room Shaper, so no lipsync. One may also need to increase audio driver and/or music player buffer sizes as lower millisecond values will have a tendency to stutter with drop outs. I did not hear any digital processing artefacts with Room Shaper engaged and as can be seen, it is limited to below 600 Hz frequency processing.

For me, Room Shaper is the icing on the cake as I am already using SOTA DSP DRC tech for 3 way linear phase digital crossovers, driver time alignment, room frequency correction and excess phase correction. The ability to control low frequency room resonances and lower mid room characteristics is a new innovation. The ability to control how much is sensed and how much effect is applied (i.e. resonances removed) allows one to fine tune to personal preference. Once I found the sweet spot where the low end sounds focused with no resonances and the lower mids sound crystal clear, no further adjustments were required, no matter what music material was played. So it is set it and forget it.

Very cool DSP innovation Thierry, congrats! Highly recommended.

I hope you are enjoying the music!

I wrote this book to provide the audio enthusiast with an easy-to-follow step-by-step guide for designing a custom digital filter that corrects the frequency and timing response of your loudspeakers in your listening environment, so that the music arriving at your ears matches as closely as possible to the content on the recording. Accurate Sound Reproduction using DSP. Click on Look Inside to review the table of contents and read the first few chapters for free.

Mitch “Mitchco” Barnett.

I love music and audio. I grew up with music around me, as my mom was a piano player (swing) and my dad was an audiophile (jazz). My hobby is building speakers, amps, preamps, etc., and I still DIY today.

I mixed live sound for a variety of bands, which led to an opportunity to work full-time in a 24-track recording studio. Over 10 years, I recorded, mixed, and sometimes produced over 30 albums, plus numerous audio for video post productions in several recording studios in Western Canada.