Use Har-Bal to tune your playback equalization

There are many features of Har-Bal we still haven't discussed in this forum. Below we will start sharing a few items. Please feel free to add yours.
Gordon Gidluck
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Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

I'm taking part in some mastering over on another website where different ME's take a single track and work on it independently. Then they all post their results and the results are critiqued by your peers.

I have done this twice and both of my tracks have have been lacking in bass compared to other entries. I have always thought that the EV MS-802's that I use were fairly accurate in terms of frequency response. However, in reviewing the spec sheet there is a bump at 80-100Hz which I didn;t know about.
http://www.eviaudio.co.jp/download/pdf/ev/ms802.pdf

So I used Har-Bal recently to try to adjust the playback equalization. Note that my focus here was to get a flat frequency response. My opinion on equalizing is that what is coming out of the speakers should be ruler-flat (for mastering applications). Room treatments should be used to resolved frequency problems with the room. But I don't try to eq my speakers to compensate for anomalies with the room. Paavo has posted a method for analyzing and correcting your room.

Since I knew I had a problem with the speaker's bass response, I recorded pink noise using an omnidirectional mic placed about 1 foot from the speaker. This minimized the effect of the room and gave me direct sound from the speaker in question. The recording was loaded into Har-Bal and I viewed the resulting frequency trace. I used this trace as my reference. Once a file has been opened with Har-Bal it creates an .anl file which can be used as a reference. To do this go to File->Reference->Open and browse to the location of your .wav file. The .anl file will be there.

Once I had a reference file for the uncorrected response, then I adjusted the playback eq using a 30-band equalizer which I will be keeping on the playback system at all times. I made adjustment (guesses) to the lows and then re-recorded pink noise through the speakers. Each time Har-Bal was used to view the resulting graph. The new wav file was compared to the reference. The process was repeated until I got a fairly flat result on the low end.

A listening test confirmed the difference. The low end was much smoother. Now that the change was made, I listened to see if I could tell the bump in the 5K region as indicated by the reference trace. Dominant frequencies can impair our ability to properly judge other frequencies. Sure enough the music sounded a bit bright to me. So the process was repeated and I adjusted the 4k-6k region down. After repeating the process a few times it still showed to be a bit low on the 2.5-3k region. I adjusted this up just a small amount.

I have made a screenshot of the frequency traces both before and after eq treatment (see below). The lighter line is the reference which shows peaks at 90hz and also around 5-6kHz. The lighter trace is the corrected response from the last wav file I recorded. Notice that the response is now fairly flat.

http://live2496.com/jpeg/ms-802-corrected.jpg

Gordon Gidluck
http://live2496.com
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

Here is a picture of the eq settings after the adjustments were made.
http://live2496.com/jpeg/rane-eq-settings.jpg
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Re: Use Har-Bal to tune your playback equalization

Post by HarBal »

Hi Gordon,

It's not a bad idea to EQ out bass problems electronically but given the nature of the problem I'd suggest the best place to monitor the response is at the listening position and not in close proximity to the speaker. It is true that close proximity measurements may give you a truer measure of how the speaker is performing but what you actually hear at your listening position will be heavily influenced by the room. By not measuring the response their you may not be getting the bass uniformity you are looking for.

Interesting to note the big peak in hf output. Is that a close proximity measurement too? If it is I'd be a little wary of it as very near field measurements can give misleading results as you may be picking up on a reactive component of the sound pressure that doesn't actually get effectively radiated beyond the near field. Again, doing the measurement at your listening position is likely to be more informative, if not a little more clouded by complexity given to the response by the room. On the other hand, sounds like you've sorted out some improvement by your method.

On the subject of ideal responses, my bent is toward a flat nominal response up to 1kHz and beyond that sloping down at about 8dB per decade. Flat sounds too bright for my ears.

On those mastering exercises, another forum member (hitmaker) has participated in those and from his assessment you tend to get a wild range of opinion and recommendation. Probably hardly surprising in my opinion, because although they may all have systems with uniform responses, their perception of the track will be heavily influenced by the level of ambiance in their rooms. I would think it would be remarkable if they all happened to have the same level of ambiance and the same ambiance colour, and as there is no standard for ambiance level and colour for mastering houses then consistency is highly unlikely. For consistency you'd need something like the THX standard for cinema sound but instead applied to mastering studios. Probably not likely to happen in my lifetime, but then again.

Cheers,


Paavo.
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

Hello Paavo,
Thank you for your insights. Definitely the next thing I should do is check the response at the mix position.
I also intend to do the "balloon test" to check to see what might be going on with the room itself.

Gordon
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Re: Use Har-Bal to tune your playback equalization

Post by Hitmaker »

Hi ,

I'd encourage you to follow Paavo's advice , and calibrate your system ( which includes speakers/room acoustics/ears ) from your monitoring/working position ...
The proportion you may be hearing 'room' ( for an audiophile ... read acoustic distortion ) , compared to total sound energy , may be as high as 60 % .... and who knows what nulls/exuberances might exist ( in the bass frequencies they are static in location ) at your listening spot ...

As Paavo's brought it up , I'd like to expand on my Prosound Web WUMP experience ...
I approached it in order to assess my techniques compared to what I thought would be a fairly standardised sample of more generously equipped rooms than my own . I had noted that many mastering houses talk of their 'objectivity' ... which would involve measurement ... and presumably the ability to adjust to a standard ...
Disappointingly , I found this not to be .... The range of comments made any consistent assessment of my system impossible .... which surprised me at the time ...

'In-box' solutions are available for eq correction , though they usually tackle phase coherency as well . To tie it in with Paavo's dreams .... the designer of the THX standard let two PhDs loose on the problem of achieving even frequency response thoughout a room ... The result was the Audyssey line of products .... These techniques have recently been made available in plug-in form ( by IKMultimedia , under Audessey licence ) .. and come with a calibrated mic to do the measurement ...

Cheers ,

Evan .
" I hate compression with a vengeance . I avoid it . I'm a great believer in the dynamic range being preserved " Alan Parsons
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

Evan,
Thanks for the advice. I appreciate you bringing this to my attention. I was quite unaware of the equalization plugin option. I would like the consistency that a system like that has to offer. After researching this a bit it seems that you have to use the VST plugin for the playback. Not all of my applications support VST, so I would ideally like to use such a system to design an eq curve that I could implement with an outboard eq. That way anything that I play back through my mixer to the speakers will have the correct treatment.

As it turns out, I also need a home receiver/tuner for the home. It seems that the most cost effective/smart option (for me) would be to get a receiver that has the Audessey system built in. Use that to program the eq and then play pink noise through it and Har-Bal it to determine the ideal eq settings. That way I would have a home receiver to use with a digital tv setup that could double as an eq'ing tool. A little bit inconvenient, but how often do I have to eq the room ? (not very). The cost of the plug-in and mic are going to be 600-700 $US vs probably 250-350 $US for a decent home receiver.

Of course a laptop computer equipped with the plugin is going to be a nice portable system for setting eq'ing rooms anywhere.

RE: ProSound WUMP
There is a variation of opinion on the tracks but if you take the average or most common opinions regarding a track I think they are pretty much on the mark. I find that the participation in this still has value for me. The amount of time involved is a bit much, but it's probably a good exercise for me every so often.

Gordon
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Re: Use Har-Bal to tune your playback equalization

Post by Hitmaker »

Hi Gordon ,

I like your cunning plan to use the resources of an Audessey-equipped AV receiver ... but there may be a little gotcha ... Do check that you don't need an Audessey installer to visit with his mic/preamp and laptop with program to dump the appropriate filter to the receiver ... If that's so ... it'll inflate your budget a bit ...

Cheers ,

Evan .
" I hate compression with a vengeance . I avoid it . I'm a great believer in the dynamic range being preserved " Alan Parsons
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

I like the idea of the plugin. However, I have to convince myself that this is better than trying to eq the room using what tools that I have already.

I have access to a pink noise generator. I have an omnidirectional mic. I could record the audio and analyze it with Harbal for longer period measurements or use the visualization meter in Samplitude for realtime.

What the plugin does easily is to take measurements at multiple listening positions and then (I suppose) average or weight the results to come up with a compromised curve that works best. I suppose that I could do something similar by mixing together separate recordings made at different listening positions. Then use Har-Bal to show me the result, which should be an averaged curve which I could inversely apply to an outboard eq.

Is there some fallacy to this line of thinking? Or will the plugin do much more?
Hitmaker
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Re: Use Har-Bal to tune your playback equalization

Post by Hitmaker »

Hi Gordon ,

Some things the IKMutlimedia plug will do 'more' ( whether this amounts to 'much' more is your judgement ) is use a calibrated mic ( i.e. with preamp tailored to ensure a flat output from the mic ) .. This eliminates the effect of any colouration from the mic ...
In addition to spectral correction ... it'll also look at timing delays between frequencies ..i.e. phase cohesion ...
And I suspect would allow much more precise frequency adjustment , particurly in the bass where the critical bands are small , compared to a graphic equaliser ..

IIRC , you had a 30-band device ... which I'd guess gives 1/3 octave bands ... If you'd like to see how much more could be done ... compare the view of any file you like in Har-Bal at 1/3 octave resolution , then at 1/12 th .... The plug uses a high resolution FIR filter ... just like Har-Bal ...

Cheers ,

Evan .
" I hate compression with a vengeance . I avoid it . I'm a great believer in the dynamic range being preserved " Alan Parsons
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

Very good point about the resolution. It sounds like I need to give this plugin a try.

Thanks again.
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

The ARC system is really good at tuning up your playback. I was blown away. The sound is so much smoother.

This thread is not so much about Har-Bal anymore, but the ARC system. ---Sorry about that. I will still use Har-Bal to do acoustic measurements. :-)

I pulled my speakers away from the wall. This should help with the bass a bit. I hope to use some acoustic treatments eventually to smooth out the low frequencies.

Just to give you some idea of the curve that the ARC system designed for the room, I have put together the following frequency traces. Keep in mind that this is the pink noise vs corrected curve. It has no sound coming from the room or speakers captured. The intention here is to just give you some idea of the correction applied. I hope to post some speaker/room traces also.

Image

The flat curve is the pink noise itself. One minute was analyzed by Har-Bal. The other curve is the shape of the filter applied by ARC. IT seems that I have an issue at 137 Hz, and also at 5.6KHz to 8kHz noted by the dips in the graph.
Hitmaker
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Re: Use Har-Bal to tune your playback equalization

Post by Hitmaker »

Hi Gordon ,

I'm glad you found that useful .... :D ...

My interpretations of the corrections applied , are of some exuberances in the areas you mention .... The 137 Hz one is likely easiest approached by trying slightly different listening/calibration positions ... ( of course , changing speaker position as well ) . I'd imagine it relates to a standing wave , determined by one , or an unfortunate combination of , room dimension(s) ... I suggest try that first , as bass traps are typically large , heavy , and expensive ... and velocity-based ( foam , fibreglass ) devices are not as suited as a pressure-based design ( heavy boxes ) , in the bass/low mids spectrum ...
Your high mids 'hump' may be efficiently controlled by a porous absorber at those positions where a mirror on the wall would reveal a speaker , viewed from your monitoring position ... both behind .. and to the sides ...

Cheers ,

Evan .
" I hate compression with a vengeance . I avoid it . I'm a great believer in the dynamic range being preserved " Alan Parsons
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Re: Use Har-Bal to tune your playback equalization

Post by HarBal »

No need to apologise for endorsing another product, Gordon! I've seen the technical literature to do with the Audyssey system (courtesy of Hitmaker) and it is entirely logical as to what they do and why. If I had the money to spare I'd buy one myself but on the other hand, I enjoy the challenge of rolling my own take on the problem and at some point in time that is what I'm intent on doing.

The frequency correction it is applying is not at all surprising and the complexity of the correction required is the main reason that graphic or parametric EQ approaches to room EQ don't work. It is a little more complex than just what you see in the frequency domain as well, since they also treat early reflects by applying echo cancellation techniques. The hardware version of Audyssey allows you to interface with a PC and get graphical views of the measure room impulse and frequency responses before and after correction. I don't know if the ARC product gives you that option.

The 120Hz correction is obviously a room mode and quite possibly the floor to ceiling mode. Given the extent of the correction, I'm guessing your system must sound a bit wooly and muffled without correction. Are your walls solid (brick / concrete) or cavity? My guess is solid going on the Q of that resonance and the degree of cut ARC has chosen to use for that mode. Given the relative strength of that mode it is probably wise to experiment with different room placement of your speakers to see if you can find a place where the speakers don't couple to that mode as well as it currently seems to do. That way when you apply ARC it won't need to work as hard to compensate and your overall sound should be better.

The high output at 5kHz is interesting. Curiously, my untreated room suffered much the same problem, though I fixed it with absorptive acoustic treatment rather than electronically. For your reference I've attached some measurements of my room response. The only real issue I have with my room is the low frequency mode at 60Hz. That stems from the size of my room but I intend coming up with a time domain equalisation solution to that problem when I have the time to implement it. The drooping top end and the bold mid range is the acoustic balance I like in a listening environment (corresponding to shorter reverb time for HF than for LF giving a warmer, mellower sound).

Cheers,


Paavo.

Frequency response
Image

Full Impulse response with diffusion treatment
Image

Full Impulse response with diffusion treatment zoomed in
Image

Full Impulse response without diffusion treatment zoomed in
Image
Gordon Gidluck
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Re: Use Har-Bal to tune your playback equalization

Post by Gordon Gidluck »

Evan and Paavo,
Thanks again for your advice and help. Distance from the speakers to the back wall is 16-17ft. Also the width of the room is 18ft at the end of the room where the speakers are and 14ft at the back of the room. A calculator application (www.mhsoft.nl) shows the wavelength of 137Hz to be 8.2 ft. That kind of makes sense.

Here are traces of the the actual room captured with the omni mic (provided in the ARC package) with and without the correction on. Look how flat the adjusted curve is even at 1/12 octave resolution. It put a smile on my face when I heard the playback. I plan to take the plugin and laptop with me to places where I work on audio projects.

Image
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Re: Use Har-Bal to tune your playback equalization

Post by Hitmaker »

Hi Gordon ,

I'm rather interested .... is there any reason you're that way on in the room .... lengthwise ???? The usual positioning would be to have your speakers backed by the smaller end .... to avoid flutter echoes , by 'pushing' your sound from speakers to behind you .... I'm imaging you'd have a slightly tighter reverb with the standard configuration as well ....

For more precision in estimating where your modes are , punch your room dimensions into here ....http://www.hunecke.de/en/calculators/room-eigenmodes.html , and select various frequencies to see where they are ... I'd use 16 ' as your width ...

Another approach you be to download/install a real-time RTA ( there's freebies about ... ??? AtSpec ) , use your calibrated mic , pump in pink noise , and wander about seeing how the curve changes ...

Great plan to be able to tune your playback to whatever room you're using .....

Cheers ,

Evan .
" I hate compression with a vengeance . I avoid it . I'm a great believer in the dynamic range being preserved " Alan Parsons
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