Yamaha YPAO R.S.C – Take Two

Introduction

In a previous blog post, I introduced YPAO R.S.C. (Reflection Sound Control), which is Yamaha’s room equalisation system. If you’re new to room equalisation, please read this post first. I will present some measurements below to show what R.S.C. is doing exactly.

Function of R.S.C.

According to Yamaha, the pure function of R.S.C. is to remove unwanted first order reflections from the sound. This should improve stereo imaging and intelligibility. As we will see there are other added benefits.

R.S.C. filters are applied before any Parametric Equalisation. In fact, all further measurements were taken using the following method on an RX-V3073 (the equivalent of the RX-A3020.

Running a multi-position YPAO with all 8 speaker positions.
Copying the flat curve over to the manual curve. This also copies the R.S.C filters as we will later see.
Zeroing out the PEQ filters manually (to 0dB on all) as this will keep the R.S.C. filters but remove any parametric equalisation. This has also been confirmed by Yamaha Japan – and the measurements that follow.

Measurements

YPAO succeeds in its goals – with some speakers and seating positions better than with others. I will show an example below with a centre speaker measurement. The centre speaker is located underneath a tensioned screen. The speaker is tilted upwards towards the listening positions. However, because of the room dimensions and multiple hard surfaces between the speaker and the listening positions on the sofa, the 70Hz to 250Hz region is a real issue with room modes – peaks and dips galore – that reduce intelligibility and are hard to deal with using PEQ alone.

Frequency Sweep

The below frequency sweep has 1/6 octave smoothing so all that is visible that R.S.C. cut some reflections in the 60Hz to 200Hz region. The green line was measured in the “through” position, while the pink line in the manual setting with no PEQs applied. Please note that R.S.C. is applying some attenuation to the signal output. The attenuation is dependent on the filters applied by the system, so it varies from channel to channel. The graph below has been adjusted to take this into consideration.

It is interesting to note that there is some activity going on above the modal region (above 250Hz). This isn’t necessarily bad as long as the robustness of the correction is taken into consideration. For example, Dirac Live does this across the whole spectrum also, but the higher frequencies are corrected, the more correlation needs to be between samples.

Now let’s have a look at the modal region with less smoothing to see what’s really going on there. Now this is more interesting. R.S.C. actually dealt with a dip in the 70Hz to 80Hz region, where the subwoofer crosses over to the centre speaker and removed some frequency build-up because of the back and side walls between the 80Hz to 200Hz.

So what is actually going on in the 70Hz to 80Hz region? Obviously no PEQ filter would be able to fill that region in since waves are cancelling each other out – as that has been tried before on this set-up. Let’s have a look at what is going on in the phase of the signal to answer that question.

Phase Measurements

As can be seen in the below measurement without any R.S.C. filters applied, there is a phase shift in the crossover region. This is quite common.

As can be seen in the below measurement with R.S.C. applied, the subwoofer and centre speaker phase are better aligned in the crossover region, therefore removing the dip in the frequency measurement. So far so good.

Ringing

Finally, let’s look at the spectrogram to see whether ringing has been improved. To be honest, ringing wasn’t much of an issue for this speaker / seating position. But as we can see in the after diagram, the crossover region looks a lot smoother and overall sound pressure levels have been better equalised in the modal region.

Subjective Listening Tests

After the above measurements were made, the PEQ filters got re-applied that smoothed the frequency response out, now having a much easier job of doing so.

Having the same PEQ applied over R.S.C. and no R.S.C. filters, though not a perfect test, the sound with R.S.C. filters applied just seemed more 3 dimensional with a better stereo image from the front and surround channel pairs. The sound of the centre channel is also improved in terms of smoothness.

What’s also clear is that the bass region is improved in terms of tightness. Even though amplitude was corrected with PEQ filters, the bass still sounded boomy in some listening positions without R.S.C. applied.

Tips and Tricks

The above does pose a challenge for those that like to have the Yamaha presence channels going along with the base 5.1 or 7.1 set-up and want to do a “full manual” configuration with R.S.C. applied. How do you measure the frequency response of these speakers after R.S.C. has been applied? Here’s a neat trick:

The easiest is to feed the left, right or surround left and right speakers with the frequency sweep signal while having the receiver in 9 channel / 11 channel stereo mode.

To hear the signal only come through the corresponding presence speaker, configure the 9 channel stereo to maximum high balance, maximum strength and maximum front / rare – left / right balance as needed. This will channel around 80% of the energy through the measured speaker, which is good enough to get an accurate measurement.

Happy Listening!

What is Room Equalisation (EQ) and why should you care?

The Perfect Loudspeaker

Loudspeaker design nowadays is advanced to a point where loudspeakers have a pretty much flat frequency response between 20Hz to 20Khz, which are the lower and upper boundary of human hearing. In an ideal home cinema, the main speakers reproduce frequencies from 80Hz up while the subwoofer is reproducing frequencies from 80Hz down (in simplified terms). Sounds below 80Hz cannot be localised by human hearing (that is you cannot tell where the sound originated from) and because of the complexities of sound waves interacting below 80Hz in small rooms, it is best to have only one (or more) carefully placed subwoofers reproducing these lower frequencies.

Here Comes the Room

It’s great we have such advanced loudspeaker design, but once you put the speakers into a room, things get messy. The sound waves will reflect off the surfaces of the walls and furnishings and interact to create drips and peaks in the frequency response, making some frequencies louder, others quieter and yet others to echo and ring as they decay.

Example of frequency response of a loudspeaker in a room

What is even more upsetting is that this is not uniform in the room. As you move your head, sit somewhere else or walk around, the dips and peaks change. If you have just spent 100’s or 1000’s on speakers, the situation is rather unacceptable. You obviously want to get the most out of your equipment.

EQ to the Rescue

There are two main ways to combat the above: digitally using equalisation and with acoustic treatments. The former is somewhat easier to implement and a lot more wife (or for our lady enthusiasts, husband) friendly.

Digital Room Equalisation is built into most receivers nowadays. Some are more effective than others. Let’s have a look at some of what is currently on the market:

Audyssey MultiEQ XT and MultiEQ XT32: Audyssey’s technology deals with the most problematic frequencies below 200Hz very well, especially when it comes to MultiEQ XT32. At the same time, higher frequencies may not sound natural to some listeners. Some manufacturers (such as Denon) allow you to apply it to only the bass frequencies for this reason. MultiEQ XT32 was also available in standalone products as SVS AS-EQ1 and Audyssey’s own branded subwoofer equalisers. They have been discontinued, however. It’s worth picking up a used one if you have a receiver that lacks a good subwoofer equaliser.

Yamaha YPAO and YPAO R.S.C: Yamaha YPAO and YPAO R.S.C are discussed in detail here. They both do a great job with frequencies above 80Hz. Fortunately, the implementation in most recent Yamaha receivers is fully editable using Parametric EQ, which gives you enough resolution to tackle most issues. The only exception to this is ringing of the modal frequencies (see below), which is important for subjective sound quality.

Parametric EQ solutions: a fully parametric EQ solution, such as the ones from MiniDSP, allow you to target the modal frequencies in the room precisely, therefore allowing the reduction of ringing / echoing of sound in the lower frequencies. A good parametric EQ is therefore essential for frequencies below 80Hz and good to have below 200Hz. Neither Audyssey or YPAO tackle ringing at these problematic frequencies.

Dirac Live: Dirac is at the forefront of audio equalisation research and seem to be overtaking even Audyssey. Their impulse response correction algorithms seem to be gathering great reviews. More recently, they are also available in MiniDSP NanoAVR DL product, which makes it affordable. It is also very easy to use for those with not a lot of experience in equalisation, but who want to get the most out of their equipment. The highest end home cinema kits feature Dirac Live.

How to EQ?

If you’re new to home cinema, at the very least read your receiver’s manual and run the automatic calibration routine with all its feature set. If you’re more adventurous, you can supplement your system with a fully configurable parametric EQ for your subwoofer to tackle the modal frequencies in your room. For this, you will need:

A parametric EQ connected between your receiver and your subwoofer
The free Room EQ Wizard (REW) software from HomeTheatreShack.com.
A compatible USB microphone.

To know more about how to measure your room and configure a Parametric EQ, the MiniDSP or HomeTheatreShack websites offers some good guides, but in essence you will have to:

Install all the software
Measure the room response (in this case for the subwoofer)
Calculate the EQ filters automatically or manually in REW
Input the filters into your choice of EQ
Re-measure the altered frequency response
Repeat until you get satisfactory results

Modal Frequencies and What to Do with Them

Modal frequencies in effect are frequencies excited or affected by the size of a room. The modal region is the region below which modal excitation happens. This is normally somewhere below 250Hz for medium to large home cinema rooms. What happens in the modal region is that certain frequencies – very accurately predicted by room dimensions – will combine and re-enforce each other or cancel each other out in a way that creates big differences in loudness and decay time of the frequency. This will make the rest of the frequency spectrum – especially frequencies close to the mode – smeared, masking detail and transparency of the sound reproduction. To resolve this, the modes need to be calculated and measured using REW using the Room Simulation module, then checked using a frequency sweep and waterfall diagram. Once the offending frequencies are found, Parametric EQ filters need to be designed to EXACTLY match the mode’s frequency and Q to rob the mode of its energy. This will help reduce decay time also and make the waterfall diagram more even.

Waterfall plot showing increased decay time in the modal region. The most offending modal frequencies are clearly visible at 29.6Hz and 71Hz. Interestingly, speech intelligibility is affected by a modal at 83Hz, even though it is not as visible on the diagram.

We have really only touched on some basic concepts when it comes to equalisation. Nevertheless, the topic deserves the attention of anyone serious about home cinema. Learn it or get a friend or consultant who has the knowledge. It makes more of a difference to the perceived sound quality than your choice of speakers or amplifier. This is because the tonal quality that you like in your speakers is a lot to do with the above graphs. Even cheaper speakers can sound fantastic with the right equalisation and a good quality subwoofer.

Yamaha YPAO and YPAO R.S.C.

What is Yamaha YPAO and YPAO R.S.C

If you have a Yamaha Surround Sound Receiver from the last few years, it will most likely have a room calibration system called Yamaha Parametric [Room] Acoustic Optimiser. In simple terms, using a microphone, YPAO will take you through a process to optimise the speakers in your room to ensure you get the best surround sound experience from your receiver. You should use it when you’re setting up your Yamaha receiver for the first time and every time you move your speakers to a new position or new room.

If you’re a beginner to home cinema, you should refer to your receiver’s manual (or read my new article here), go through the YPAO process and stop reading here. At the same time, if you are an advanced reader and want to understand how to get the very best out of your receiver, keep reading. Since there isn’t a lot of information on the internet about YPAO, this article will go into some fairly advanced topics. Please read the basic and intermediate articles on SimpleHomeCinema first if you’re new to home cinema. Our advanced articles will not explain basic terminology.

Please note that not all statements are backed up by measurement graphs, but the article was written after being in email communication with the engineers at Yamaha Japan who designed YPAO (with the help of Yamaha Australia, thank you!) and taking hundreds of measurements and configurations for testing. These may be published at a later time. For the benefit of contributing to the community, the findings are published without wait.

The Difference between YPAO and YPAO R.S.C

Basic YPAO will do the following:

Measure and set speaker delays (called – inaccurately – distance)
Measure and set speaker levels / volume
Measure the frequency response of your speakers and use a parametric equaliser (PEQ) to flatten the frequency response of the speakers/room in the frequency domain only (what it is doing really is match the timbre of the speakers to each other)

YPAO R.S.C (R.S.C. stands for Reflected Sound Control) is more advanced. It actually has TWO sets of filters:

It will measure the impulse response of the main speakers (not the subwoofer even if the model has sub EQ) AND will create filters that will modulate BOTH the phase and the frequency of the response. This is to allow for removing the first reflection of the speakers in the room and it allows YPAO to tackle both the dips and the peaks in the frequency response. YPAO basic will only be able to tackle the peaks effectively and do a hit or miss with the dips. This is true of any type of parametric EQ. These filters are not actually displayed on the screen and are not editable.
The second set of filters are only in the frequency-domain with a minimum phase: these are the PEQ filters that are used in the YPAO basic equalisation. But here, more broad filters can be used since the main / most difficult issues in frequency response have been corrected.

This is why manual editing of filters for YPAO and YPAO R.S.C have to be done differently. Let’s have a look…

How to tweak YPAO and YPAO R.S.C manually

So why would you tweak YPAO and YPAO R.S.C.? There are two reasons:

Even when they have the capability on the higher-end receivers to do subwoofer equalisation, they don’t actually set filters that work in more difficult rooms. Yes, the subwoofer is the most important speaker to equalise.
YPAO and YPAO R.S.C. don’t always get the filters right. Sometimes a manual calibration will get more precision.

What do you need to manually calibrate YPAO and YPAO R.S.C.?

A high-quality USB microphone like the UMIK-1 OR if you have a receiver with YPAO R.S.C. the microphone that came with your receiver and a cheap USB sound-card with microphone line input. Please note that I have tested the YPAO R.S.C. microphone against a calibrated UMIK-1 and the microphone is accurate enough to calibrate to 1/6 octave resolution. You should NOT be working with a higher resolution anyway, especially since YPAO can only do about 1/3 octave resolution accurately, which is plenty to get your speakers sounding fantastic.
REW – Room EQ Wizard. You will need to Google this program and download it from Home Theatre Shack.
An strong will to learn and succeed if you’re new to equalisation.

How to set up the receiver

All Yamaha receivers give you the option to copy one of the equalisation curves to the manual curve for editing. This may be a good starting point for you. To find out if it is, measure your speakers both with the EQ off and on and see which response is flatter / closer to where you want it to be. Start there.

Alternatively, clear the manual PEQ settings and start from scratch by measuring the response.

IMPORTANT POINT!!! With YPAO R.S.C, when you copy one of the YPAO curves (such as Flat or Natural), the Impulse Response Filters (IRF) will also be copied, even though they are not editable. This means that you need to copy the curve and then MANUALLY set all filters to 0 decibels and measure your speakers that way if you want to start from scratch but still keep the IRF filters.

A proof for this is measuring the manual EQ on with all PEQ filters in the 0dB position and EQ off (called YPAO Through) to see what the IRF filters are doing. You will notice a difference and that is the first layer of filters being applied by YPAO R.S.C. The following diagram illustrates the difference. The centre speaker was measured both with no EQ (pink line) and with the manual setting with all EQ filters set to 0dB and only IRF filters active (darker purple line). You can see that the purple line is smoother especially in the 80Hz to 500Hz where YPAO R.S.C. is most active. Ignore the subwoofer measurements (below 80Hz).

How to equalise your speakers

Mathematically, YPAO’s 1/3 octave resolution is enough to get a flat enough frequency response for all your speakers. This is in spite of the fact that people on the forums like to complain about YPAO not giving us a higher resolution.

Adding YPAO R.S.C to the mix and you have way more resolution AND manual control to get excellent sound rivalling equipment costing 10x as much, if you’re willing to do the work. Here are some charts to prove this from a purely mathematics point of view, and then I’ll tackle reality. Darker purple line is the original response. The pink line is the new predicted response with only 6 filters, all configurable in YPAO.

As you can see on the before and after frequency response curves calculated by REW, you can match the response of all speakers within 2db of the desired curve using only the YPAO PEQs. That is not perfect but pretty close.

Ok, so how does this work in reality? REW’s predictions for cutting filters will be 95% spot on regarding how the PEQ filters will behave. The other 5% is slightly different behaviour OR – in the case of YPAO R.S.C. – an interaction with the Impulse filters. So set the filter, and re-measure.

Peaking or boosting filters will almost always not behave how you expect them to and may even cause audible artefacts. This is because dips in frequency response are most often than not will be due to standing waves, which PEQ cannot correct effectively or if it can, it will only do so for certain listening positions, while produce artefacts for others.

This is why you should equalise using only cutting filters if you can or if you cannot, use careful listening and re-measurement of all listening positions to ensure the filter hasn’t caused artefacts. To be perfectly honest, having played with different PEQ filters with or without impulse filters applied, in 99% of cases narrow Q boosting filters used to tackle sharp dips will produce some kind of artefact that is audible to trained ears. For untrained ears, this may not be so, but it is best to leave them be or lower the rest of the frequency spectrum instead.

There is a lot more to say about YPAO, but this is the take-away:

YPAO’s resolution is enough to correct frequency response to 2dB to the desired target. It will take time to experiment with the filters, though, to get this right.
YPAO R.S.C. applies impulse response filters that are not editable but will copy over to the manual setting.
Use cutting filters only to avoid audible artefacts, especially if you have any critical listeners in the audience. Otherwise re-measure all listening positions.
Use the subwoofer EQ on the higher-end models to equalise your subwoofer. Again, use only cutting filters here and tackle dips in the response by moving the subwoofer to a more ideal location in the room. PEQ is not there to do that.

Should you have any questions regarding more advanced set-up of your Yamaha receiver, please contact us at Simple Home Cinema. Happy listening!

Please note that a follow-up to this article has been posted here.