# How to measure a room's accoustics



## ledgerdc (Aug 4, 2011)

I tried to find something on this, but am apparently being search challenged.

I have recently done some major overhaul to my HT and would like to measure the new acoustic properties. I don't really have a clue as to what is needed to do this. I'd like to explore the DIY track before trying to hire someone to come in and do the measurements.

Any advice / direction on what I should be doing (equipment, method, reference links, etc.) would be greatly appreciated.


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## Andre (Feb 15, 2010)

I too would like to know if there is an "on the cheap" way of doing this.


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## bpape (Sep 14, 2006)

Download Room EQ Wizard. It's on this site in the REW forum. All you need is a computer and a Radio Shack SPL meter and a way to hold the meter steady where your head is when seated.

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> Download Room EQ Wizard. It's on this site in the REW forum. All you need is a computer and a Radio Shack SPL meter and a way to hold the meter steady where your head is when seated.
> 
> Bryan


Is the soundcard with line-level inputs and outputs on the REW Getting Started page a recommendation then, not a rule?


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## bpape (Sep 14, 2006)

I believe it is a requirement (can't use a mic input) but most laptops have that and the vast majority of PCs made within the last few years will also have them.

Bryan


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## Tooley (Jan 2, 2011)

bpape said:


> I believe it is a requirement (can't use a mic input) but most laptops have that and the vast majority of PCs made within the last few years will also have them.
> 
> Bryan


My laptop only has mic jack is there any other way to use my RS SPL meter with my laptop


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## bpape (Sep 14, 2006)

You can use an external USB soundcard such as the Sound Blaster models. They will give you the required ins and outs converting to USB for laptop interface.


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## SAC (Dec 3, 2009)

Asking what is necessary to measure room acoustics is a rather vague question.

And from the remaining responses, it seems that most consider only the ability to measure frequency response and SPL levels to be sufficient.

I guess that depends upon what one considers to be "room acoustics".

The fact is, such an approach is ONLY sufficient to generate frequency response waterfalls for observing modal behavior below ~250 Hz.

If that is your world of acoustics, then that is fine.

But there is a MUCH LARGER critical world of behavior that occurs above the modal region what is called the specular region, where sound ceases to behave as standing waves and acts instead as focused rays (specularly). It is in this region that localization, imaging, tonality and intelligibility is determined. In fact, for this region you will not use the frequency response at all - as it merely shows the results of the interaction of many variables without affording you any insight into what any of those various signals are or what they are doing.

In order to gain such insight, you are going to need to use time domain measurements - in particular the Envelope Time Curve or ETC. This measurement will allow one to see and identify EACH individual energy arrival in terms of arrival time and gain, and from this determine the precise direction of travel and temporal and spatial characteristic (sparse, diffuse, etc.) of the energy arrivals. And from this information, dependent upon the desires acoustical room response model desired, one will them surgically select and apply the appropriate treatment materials (absorption, reflection/redirection, diffusion) to specific locations sufficient to achieve the desires acoustical room response.

And for that, you are going to need more than a large capsule SPL meter as an input.

For that you are going to need an small capsule omni microphone. 

And if I might make a wry observation, too often this becomes for many "the cheapest mic they can buy", which generally means the Behringer CM8000 or a Dayton EMM6. These can work just fine. Just realize that you get what you pay for in terms of unit to unit variability and the lack of included calibration curves.

Additionally, it would make sense to obtain an inexpensive GOOD EQUALITY mic pre-amp that exhibits some semblance of linear phase and amplitude response! It amazes me that folks resist doing this, demand flat measured responses from said equipment, scrimp at this stage, and then have no problem spending $150-$750 for a magic EQ unit thinking that will solve all of the room problems - which it most definitely will NOT. Common inexpensive entry units are the ART Dual USB Pre and the M Audio MobilePre USB - both of which feature phantom power! Additional units that can work range from the PreSonus FireStudio Mobile up to the much higher end Axys D-Audio USB Pre, etc.

The real irony to objections to spending a few bucks more, that will be returned in capabilities, is that one can, if they decide they are finished measuring and treating their room, resell the equipment to others and recoup their costs.

{Or you can spend $300+ for an Omnimic or XTZ setup totally incapable of doing more than frequency domain measurements (meaning you are limited to modal analysis) all because some folks are apparently incapable of determining interconnect jack types, yet upon having someone else do that for them at a cost of ~$150+, they will suddenly experience an epiphany and suddenly study and understand measurement and analysis concepts MUCH that more complex than interconnect types - and amazing personal transformation indeed! The shame is, that after such a miraculous epiphany occurs, they are stuck with a test platform too severely crippled to accomplish what it is they need it to do! What a DEAL! :rofl2:}

So, it all depends upon what one's goals are. 

If all you are concerned about is LF room modes, you can get by with the current orientation. 

If, however, your sights are a bit higher, and you wish to avail yourself of the abilities and insights that have resulted in a literal quantum leap in acoustics reflecting what has been learned in acoustics over the past 40 years, you will want a more capable front end preamp and mic capable of taking advantage of all of the tools REW affords you. And if you take a small amount of time to learn what the various behaviors are that they can illuminate, and how this behavior effects the perception of sound within the space, and then, based upon that, learn how various acoustical room response models can be used to optimize the choice and placement of various room treatments in order to achieve the precise response you desire.

Thus, I would encourage you to set your sights a bit higher, and to rearrange your priorities a bit , as a small investment here will provide a *much* greater return than will additional money spent on any particular piece(s) of electronic gear; and the substantial rewards are achievable with only slightly more effort.


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## bpape (Sep 14, 2006)

Agreed. That said, 'on the cheap' and getting a general feel for what is happening both in time and frequency domains can be had with REW. The RS meter mic, while certainly not 100% accurate, does at least have a correction plug-in available for REW to at least mostly compensate for the frequency response problems. Those remaining inadequacies will at least be consistent among measurements - and that's what we're trying to do is measure relative change - not absolute response.

For most home users, this is a 90% solution that will at least allow tweaking of relative gains and losses in terms of seating, speaker, and sub position along with identifying reflections, modal problems, etc.

Sure - there's a lot more to it but this is not about a professional studio setup. This is about home theater and getting it the best you can given budget and existing room room restrictions.


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## SAC (Dec 3, 2009)

I am not sure why this needs to be debated.

Modal response is NOT "90%" of a room's response unless one willfully and myopically wants to focus only on LF modal response!

As I said, it all depends upon what one's goals are. But I think it is VERY important that one be made aware of the significant trade-offs involved in choosing the path, as that chosen hardware configuration - not one's choice - will definitely impose hard limits upon what one can do. 

If one knows that that is ALL they want to do - and that moving beyond that point will require a return and a complete re-investment in a mic pre-amp and a microphone that can be had for not much more than what they are buying now (note, you will NOT need to buy a separate SPL meter who functionality is included in REW!), then fine. 

But they do it with an awareness of the trade-offs they are making. It will not be because someone else has arbitrarily decided for them that 'what they are getting is sufficient for _their_ needs'. 

And if one will recall, the original question was NOT "what is the minimum amount of gear that is required to measure* only *the modal response below ~250 Hz in a room."

This is rather ironic as the treatment of modal issues is considered a necessary pre-requisite to addressing "room acoustics" in many circles.

Thus ALL of the options should be presented without others determining what is sufficient for 'them'. And then based upon what THEY decide they are interested, THEY can determine what path THEY want to pursue based upon a complete presentation of the options and capabilities of the system. 

And the realm of behavior ABOVE ~250 Hz is a VERY important area that will return significant benefits if one is not scared off by others telling you that you either don't need to worry about it, or that its too kompleekated!

And it grows a bit old that so many (in so many places!) seem to have determined that "common folks" are incapable of learning and using the same tools that the "pros" use, when the availability of tools such as REW, FuzzMeasure (on the Mac), and ARTA have brought the power of most (but no, not all) of the tools the "pros" use to the "common folk". And that their utility is very easily accessed.

If they choose to ignore the_ significant _advances in the behavioral region above the modal region that have revolutionized small room acoustics in the past 40 years, fine. But I would prefer THEY make that decision, and that they do not fore go it simply because we have either simply failed to inform them, or because some have told them and scared them into thinking that "it's too complicated"! Which it is NOT! 

But then, still others are all only too glad to introduce others to the basics and then to sell them the additional functionality per their business model.

And that is fine, provided that people make an informed decision freely, and not because of the omission of pertinent information that would enable them to pursue it themselves if they so choose.

And for those intimidated by the tools, or scared by others dire warnings of disaster, but who are willing to take a few days to familiarize themselves with the concepts and the tools, you can PM me and (provided you set up Yahoo Messenger or Skype for voice communications) I will be glad to help you with the USE of the tools (after you have configured the system and installed the physical loopback connection) and to help you understand basic room response concepts and models that are common to the majority of the accepted acoustical response models, and in particular the use of the ETC response tool, in a manner sufficient to interpret, analyze and to select and precisely place treatments in accordance to a desired and achievable acoustical response model - _without charge_ - based upon 24 years of applied hands on use of the ETC response.


The larger issue is what makes threads like this so fascinating.

It begins with a question asking what is necessary to measure a rooms acoustics. And then instead of accurately presenting an overall explanation of what is necessary to do that, folks systematically dumb the discussion down by assuming they don't need that of which they are not familiar until we reach the point of axing why anyone wants to make measurements at all, as not only do they not understand them, but they are not willing to do any appreciable treatment. Its like the proverbial metaphor of crabs in a bucket... Heaven forbid we should actually try to explain what can be done, how it should be done, and what can be learned and applied from such an explanation. But if we actually did what the question asked initially, folks might not need to continually ask what measurements care good for or how to make and interpret them! After all, how many places can one cite that explain the procedure for interpreting and actually using an ETC response? That question alone should keep you busy for a while!


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## bpape (Sep 14, 2006)

Not a matter of debate - a matter of reality and context.

I never said that modal response was 90% of the room response. I said, if you have REW and can measure what it allows you to measure (even with a RS mic and compensation file) it will give you a 90% solution including impulse response, etc, frequency response, decay times, etc. at a very reasonable cost. You can put as much or little time into learning the tool as you want and dig as deep as you want. Regardless, it's a step in the right direction by knowing what is going on in your room, how various positional changes make relative changes (what is causing the problems you see), etc.

Bryan


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## SAC (Dec 3, 2009)

For anything other than modal response you_ will_ need a small capsule omni mic such as the entry level Behringer or the Dayton mics that require phantom power - which then requires either a separate ~$70 phantom power unit or a mic pre-amp capable of better spec performance and integrated phantom power. 

The fact is, the large capsule SPL meter as mic will not provide very accurate ETC information. I wish it would, as many of us who do this routinely would LOVE to save some money and not worry about encounters with dreaded chair carts and drops involving EXPENSIVE matched mics. It would indeed be nice to be able to use meters that can almost literally be thrown across the room without damage. 

But rather than spending $40+ for a limited SPL meter, put it towards an ~$79 mic pre and the ~$45 mic and have a platform limited by what YOU want to do with it, rather than one fundamentally limited in capabilities by the hardware. 

And when you are finished with it (if ever), you can sell it and recoup your investment.

(Just note, for those curious, this is by NO means a pro configuration where you are looking at a pre with performance (phase linearity) in the region of the Axys D-Audio USB pre and a higher end mic. But it will be_ fine_ for general utility purposes.)


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## Andre (Feb 15, 2010)

I personally don’t want to go that far. I have no acoustic panels, I put my sub “where it fit”, and my seating is couches angled in from the side walls since we like to lie down to watch movies. 

Sure eventually I would like to get real theatre seats…etc But, I consider this a hobby and as a hobby I wouldn’t mind doing a few inexpensive experiments to determine if anything is totally skewed, then make note of it and come back here to ask people like Shirley…ah.. Bryan if there is an easy way to fix it, like add some heavy curtain to this wall, or get this and put it in the corner…etc

Beyond that I would have a pro come in like I did for calibrating my TV


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## SAC (Dec 3, 2009)

What is meant by "you don't want to go that far"?

You don't want to know what is actually going on int he room in terms of modal behavior and of specular reflections in the room? 

One is displayed with waterfalls, and the other with time domain ETC responses.

Knowledge of both is what makes any options possible. 

Then you can decide _precisely_ to what extent you want to 'do something'.

With such basic information you then can determine precisely what behavior has the most detrimental effect and you can simply make the necessary adjustment to make the greatest improvement with the least investment!

But with out such an understanding, you are simply 'doing something' and randomly 'changing something' and moving problems around! And THAT is the REAL waste of time and effort!

Instead we begin with an assumed assessment of what is happening along with treatments (that will only exacerbate the problems) and then consider the possibility to work backwards to discover what is actually happening! 

And example is your suggested placement of curtains that will ONLY mitigate the high frequencies (that we actual do not try to treat as their energy content is so low and they are absorbed so easily anyway!) while doing nothing to mitigate the indirect mid frequency energy that is the real cause of problems - assuming of course that you even place them at significant points of boundary incidence! Curtains will simply deaden the room and they will NOT effectively remove the mid range energy (with the much higher energy content) that still causes the problems. (As many seem to worship Toole, here is his assessment of such treatment "In particular, acoustic absorption, diffusion, and reflection must be broadband, ideally starting below 200Hz. ...Typical 1˝ or 2˝ sound panel most often affixed to walls works only at relatively high frequencies, and acts to effectively turn down the tweeter with no effect on the midrange or up¬per bass, thus unbalancing the sound.")

You don't need ANY measurements to simply guess and to actually make problems worse!

The REAL problem here is that few have taken the time to actually discover what issues are important beyond having heard the cliche that 'reflections are bad', and as a result few know what the measurements can uncover and the utility of such measurements. And without that basic understanding, it makes little sense to determine what use measurements will provide if one so limits their options prior to even taking the time to learn about eh basic behavior in a small acoustical space and what measurements can tell you and also what simple treatments can be made _*IF*_ they are _*properly applied*_.

But as so many have already decided what treatments are, or are not, already appropriate, as well as what are the underlying nature of the Real problems, one might wonder why actual measurements are even worthwhile!? 

And THAT is the REAL reason that measurements are necessary! To discover the REAL issues at hand. And THEN prudent courses of action can be determined. And these actions can be as limited or as extensive as one desires, but any action can be predicated upon addressing the biggest return on expense and effort in relation to having precisely identified REAL issues and thus to solve REAL problems and to make real quantifiable improvements, and not simply to address assumed or imagined issues.


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## Andre (Feb 15, 2010)

Ok..so if I don't have a laptop, or a spl meter (but its on my list if toys) or know the first thing about REW or how or why I want or don't want reflection, diffusion, refraction....etc. 

considering my current seating arrangement (couch, lying down, side wall) I just thought there might perhaps be something cavemanishly simple I could do that might help me adjust my current systems levels, perhaps the eq in the avr..etc that could possibly make the room sound better.


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## SAC (Dec 3, 2009)

Aaaaah....Yeah, there are a few things you could try.

But seeing as this was a thread asking "How to measure a room acoustics" and you are asking everything_ BUT_, it might be prudent to start a separate thread addressing your concern and providing information about your room and system and folks can make appropriate suggestions.


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## Kaisergrendel (Jul 19, 2011)

SAC said:


> For anything other than modal response you_ will_ need a small capsule omni mic such as the entry level Behringer or the Dayton mics that require phantom power - which then requires either a separate ~$70 phantom power unit or a mic pre-amp capable of better spec performance and integrated phantom power.
> 
> The fact is, the large capsule SPL meter as mic will not provide very accurate ETC information. I wish it would, as many of us who do this routinely would LOVE to save some money and not worry about encounters with dreaded chair carts and drops involving EXPENSIVE matched mics. It would indeed be nice to be able to use meters that can almost literally be thrown across the room without damage.
> 
> ...


SAC, I *almost* bought a Galaxy 140 till I read this. I see you're passionate about telling people how to put money where it matters. I am the same when people ask me about photography gear, which is my first interest.

My question to you is, if your suggestion is to get a mic+preamp instead of an SPL meter, how does REW calibrate SPL, and which Behringer or Dayton mic models are you talking about? Could you also point me in the direction of a good preamp to start with?


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## bpape (Sep 14, 2006)

You'll still need some sort of level meter to set your system at the reference level to know how to adjust REW sensitivity.

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> You'll still need some sort of level meter to set your system at the reference level to know how to adjust REW sensitivity.
> 
> Bryan


Ok, I think I get it, I have a cheap SPL meter without inputs, so I plug in the calibration mic and adjust the REW calibration setting till it matches the SPL meter reading. Am I right in thinking this is a popular mic for calibration? 

http://www.amazon.com/Behringer-ECM8000-Condenser-Microphone-Omni/dp/B000HT4RSA


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## bpape (Sep 14, 2006)

While not optimal, the Behringer is usable.

To do the calibration, you use your SPL meter to adjust your system volume to the desired level - 75-80db). Then use your measuring mic to adjust the sensitivity in REW so that it's meters read the same level (without changing your actual system level).

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> While not optimal, the Behringer is usable.
> 
> To do the calibration, you use your SPL meter to adjust your system volume to the desired level - 75-80db). Then use your measuring mic to adjust the sensitivity in REW so that it's meters read the same level (without changing your actual system level).
> 
> Bryan


Thanks, that makes perfect sense.

Yeah I'm not looking for optimal solutions, I'm looking for what I can afford with my disposable income and my free time  That said, I still want to make the right choices within these limits. How's this for a preamp? 

http://www.adorama.com/BE802.html


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## bpape (Sep 14, 2006)

Not familiar with that but you don't need the mixer and all the other stuff. Something like this would work fine and also allows USB connections

http://www.zzounds.com/item--ARTUSBDPPS


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> Not familiar with that but you don't need the mixer and all the other stuff. Something like this would work fine and also allows USB connections
> 
> http://www.zzounds.com/item--ARTUSBDPPS


At $30 more than the mixer, do you think I'd be paying for any additional quality? Is the USB connectivity any use to REW?


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## bpape (Sep 14, 2006)

I think it's a better product overall as it's concentrated on being a mic pre/interface rather than a lot of $ being spent on a mixer, EQ, meters, headphone out, etc. you don't need. $50 for all of that and it's got to be pretty cheaply made.

The USB interface can be quite handy.

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> I think it's a better product overall as it's concentrated on being a mic pre/interface rather than a lot of $ being spent on a mixer, EQ, meters, headphone out, etc. you don't need. $50 for all of that and it's got to be pretty cheaply made.
> 
> The USB interface can be quite handy.
> 
> Bryan


Thanks, does the USB work with REW at all? It's just unlikely I'll use it for anything else. What do you think of this amp? http://www.adorama.com/ROLMP13.html


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## bpape (Sep 14, 2006)

Specs look OK. 

USB is just a handy way to connect if you'd ever have another use for it. If not, then what you just linked to would likely be fine.

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> Specs look OK.
> 
> USB is just a handy way to connect if you'd ever have another use for it. If not, then what you just linked to would likely be fine.
> 
> Bryan


Thanks!


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## SAC (Dec 3, 2009)

Go with the ART Dual Pre. It offers dual channel use which is VERY useful for any time measurements you might need. With only a single channel you WILL be limited in the measurements you can take.

The real additional functionality and quality is well worth ~$20 difference.


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## Kaisergrendel (Jul 19, 2011)

SAC said:


> Go with the ART Dual Pre. It offers dual channel use which is VERY useful for any time measurements you might need. With only a single channel you WILL be limited in the measurements you can take.
> 
> The real additional functionality and quality is well worth ~$20 difference.


Thanks, could you explain briefly how those measurements work with two channels? Will it entail additional costs over a single channel setup like buying two calibration mics?


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## SAC (Dec 3, 2009)

The ability to perform 2 channel FFT is substantial. Without going into lots of detail, dual channel FFT allows one to compare one channel with the other to show the difference. A very useful and powerful capability that significantly extends the functionality of the platform.

Also, if you are going to do time based measurements for specular reflections (above ~250 Hz modal behavior) that directly impact localization, imaging, intelligibility and tonality, you will want the ability to configure a hardware loopback using the additional channel (this is simply a feedback loop provided by a simple jumper connecting the output of the second channel with the input of the same channel, providing a timing reference allowing for the compensation/elimination of the hardware propagation delay/latency - the time it takes the particular hardware setup to 'get its act together'). This is necessary to provide the actual travel time of the signal from source to mic.

Bottomline, you will have a future oriented setup that will allow you to do essentially whatever you want to do as provided by the software platform, be it REW, FuzzMeasure (on the Mac) or with ARTA, without being limited by the hardware and having to replace the unit with a pre-amp such as the Dual Pre later in order to acquire these very useful features. Also, if you decide you are finished and wish to tell it, you can recoup most of your money as a dual channel pre-amp is useful for many purposes from testing to stereo recording. Conversely, I would not generally buy a single channel pre-amp as it is too limited in its applications.


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## Kaisergrendel (Jul 19, 2011)

SAC said:


> The ability to perform 2 channel FFT is substantial. Without going into lots of detail, dual channel FFT allows one to compare compares one channel with the other to show the difference. A very useful and powerful capability that significantly extends the functionality of the platform.
> 
> Also, if you are going to do time based measurements for specular reflections (above ~250 Hz modal behavior) that directly impact localization, imaging, intelligibility and tonality, you will want the ability to configure a hardware loopback using the additional channel (this is simply a feedback loop provided by a simple jumper connecting the output of the second channel with the input of the same channel, providing a timing reference allowing for the compensation/elimination of the hardware propagation delay/latency - the time it takes the particular hardware setup to 'get its act together'). This is necessary to provide the actual travel time of the signal from source to mic.
> 
> Bottomline, you will have a future oriented setup that will allow you to do essentially whatever you want to do as provided by the software platform, be it REW, FuzzMeasure (on the Mac) or with ARTA, without being limited by the hardware and having to replace the unit with a pre-amp such as the Dual Pre later in order to acquire these very useful features. Also, if you decide you are finished and wish to tell it, you can recoup most of your money as a dual channel pre-amp is useful for many purposes from testing to stereo recording. Conversely, I would not generally buy a single channel pre-amp as it is too limited in its applications.


Thanks, I guess I'll look into that too.


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