蓝牙音频测试 / Bluetooth Testing Seminar May 17, 2021 - 3:57 pm June 3rd 2021. 10am (China Time) In this 1hr online seminar, S&V Samford presents Les Quindipan of Listen, Inc. And Kristopher Hett of Portland Tool & Die demonstrating how to test Bluetooth devices. True Audio: Audio Spectrum Analyzer and Loudspeaker Design Software Create your own audio measurement system starting with TrueRTA software and your Windows PC. Then add a measurement microphone and USB interface and you have a full audio/acoustic test setup.
How often is it that you can get something for your systemfor nothing? Almost never. Below are six of our favorite free pieces ofsoftware that we think every audio enthusiast should download and try out. FromCD ripping to improving your ability to critically listen, this list hassomething for everyone. Enjoy, and let us know if you have any othersuggestions by posting in the comments below.
1.Exact Audio Copy
Exact Audio Copy, or EAC as the cool kids say, is theSwiss Army Knife of CD ripping, copying, and burning. The goal of this program,as the name suggests, is to rip audio from a CD without adulterating the file.It does this through jitter correction and read error detection. When rippingin “secure mode”, EAC reads every audio section at least twice, or relies onextended error information that some drives are able to return with the audiodata. Let’s say there is an error while reading a disc, the program willre-read up to 82 times, compare the results, and give you the best copypossible. If the program is less than 99.5% sure the audio stream is correct,it will alert you with a read error. Beyond accuracy, the program is endlesslycustomizable while still managing to be easy enough to use for the less-technicaluser.
Exact Audio Copy
EAC can save the ripped files in uncompressed WAV format,and supports external MP3, WMA, flac and OggVorbis encoders. It can alsodecompress some files back to WAV. There are a host of other features, like CDwriting, pre-track gap detection, and metadata editing. If you are looking totake your CD collection and turn it into a digital library, EAC is the way todo it.
2. TT Dynamic Range Meter
We’ve written about compression and the loudness war foryears (see: CurrentTrend in the Recording Format Arena and CDCompression Depression for two examples), and we’re not alonein our frustration. The Pleasurize Music Foundation created TT Dynamic RangeMeter with the goal of fighting the over-compression of music. The programtells you the dynamic range of songs, so you can find out if you have justpurchased a quality recording or not. One fun use of DR Meter is to compare differentreleases of the same song or album. The program is incredibly easy to use,simply select the track or folder you want analyzed ... and that’s it. It takesa few seconds for the program to spit out a number telling you the dynamicrange of the album or track. It can also create a log file telling you thedynamic range of each individual track if you scan an entire folder. Accordingto their website, a DR of 7 “is low for rock music or very low for Jazz, [but]it is quite acceptable for electronic club music which has nowadays oftenvalues below DR4. All values above DR12 have generally a high dynamic quality.”
DR Meter Offline DR Meter Log Sheet
DR meter comes in two flavors, what they call an offlineversion (pictured above) and as a foobar2000 component. For those of you who are wondering what foobar2000 is, checkout our MusicPlayback Software Comparison. If you do decide todownload DT meter, we encourage you to sign up andsupport their campaign to end the loudness war.
3. Room EQ Wizard
Speaker Testing Software Reviews
Room EQ Wizard, or REW, was one of the original room andloudspeaker measurement systems available to the home theater enthusiast. Oncesetup properly, it’s a joy to use. Actually, I find it much more intuitive thanOmnimic, a costly alternative. REW is packed with useful features, the mostprominent being an SPL meter, RTA, waterfall plot, and spectrogram. REW canhelp you figure out the best placement for speakers, listening position, andacoustic treatments. Figuring out how to use all of the functionality packedinto REW can be a little tough at first, but there is a large online communityto provide support.
RoomEQ Wizard
Like we said, once up and running, REW is a powerfulpiece of software. However, getting it up and running can be difficult, andresults can be inaccurate depending on the quality of measurement equipment youare using. You will need to invest in a microphone, cables, tripod, andexternal soundcard (external soundcard is optional). You may also needsomething like the NadySMPS-1X phantom power supply for the mic, depending on thefunctionality of the soundcard you purchase. If you are willing to spend someextra time during setup and invest in decent quality measurement gear, you willbe rewarded. For people who want a more seamless experience, kits from Omnimic or XTZ(review in progress) come with everything you need and work right out of thebox with little to no setup.
4. Harman How to Listen
This is the only program we know of that is designed toimprove your critical listening abilities. Originally created to train Harmanemployees, it has been made available, for free, to the public. It’stechnically still beta, but it has been that way for a number of years, sodon’t expect an update anytime soon.
2 Band Test 24 Band Insane Test
The program works by asking listeners to identify how atrack has been manipulated. For example, the image above-left shows a verybasic Band ID exercise. The user can switch be an unaltered “flat” version ofthe song, and the modified “EQ” version. The goal is to identify which of thetwo Eqs shown is being applied, number 1 or 2. The tests become increasinglydifficult. Above-right is an image of the most difficult Band ID test theprogram has to offer. As you can tell, the tests become very difficult. Thereare a number of different training exercises, including reverb, coloration, andnoise. If you become tired of the tracks that come with the software, you caneven upload your own to demo.
Speaker Testing software, free download
5. Audio DiffMaker
Have you ever made a change to your system and wonderedif there was any actual change in the sound? Let’s say you just spent $3,800 perfoot on a Audioquest WEL Signature power cable,and you want to know if that made any difference, audible or not. That’s thepurpose of Audio DiffMaker. You record a reference track. This can be done with a mic to capture the actual sound output from your speakers, or using various other methods to capture the audio output from a device. Next, make the change inthe system, and then record a compared track. The software compares the twotracks and extracts the difference.
Diffmaker Screenshot
The designers (Liberty Instruments) went through a lot oftrouble to ensure accuracy. For example, it automatically accounts for samplerate drift and level differences, so the difference recording is only what hasactually changed between the two recordings. Anyway, that’s what they claim,and they seem to have taken all of the necessary steps to achieve that goal.Note that this system does not require your equipment be completely linear orof the highest quality, by its very design all of the characteristics of yoursystem are part of the reference and comparison recordings. Even though theconcept of Audio DiffMaker is simple, be warned that its actual implementationcan be difficult and time consuming. The two recordings need to be verycarefully taken so as to isolate only a single variable. Still, if you arereally into small system tweaks and DIY projects, this is a fun program to seeif each change makes a difference or not.
6. Audacity
Audacity has been around for a long time, and like someof the other software on this list, is opensource. Unlike the other software onthis list, which serve specific purposes, Audacity has a wide range of uses.Essentially, it’s a sound recording and editing program. It can record liveaudio or computer audio, and then be used to edit the recording. One of thecommon uses of Audacity is to record and edit podcasts, and is employed by AVrant podcast forthat very purpose. Quality is also key with Audacity. It can import and export WAV,AIFF, AU, FLAC and Ogg Vorbis files, and record at 24-bit depth and 192,000 Hzsampling rate (384,000Hz on OS X and Linux).
Audacityscreenshot
One of the reasons it made this list is because of a cool“show clipping” feature. The program will highlight red any portion of theaudio waveform that clips. Like DifMaker, this can be used to compare thequality of different tracks. The above screenshot shows a song from HDtracks’free sampler. The image below shows Dire Straits “Walk of Life” downloaded fromiTunes … notice any clipping?
ImageCourtesy of AVrant Podcast and their loyal listener John
Conclusion
We thoroughly enjoy using the software on this list, andhope you will too. We didn’t cover everything out there, so let us know whatyour favorite software is. Finally, we want to say a quick thanks to all of theindividuals who invest their time and effort into creating software that therest of us can use for free. Richard Stallman would be proud.
Speaker Testing and Analysis
Now that you have built your speakers, it is time to test them. You will need a microphone and a computer with a microphone input & headphone/line-out output.You will also need software that generates test tones at different frequencies and then reads back those tones using the microphone connected to the computer.
If you don't have a microphone for testing, you may want to build your own instead of spending a lot of money for one.Check out our page on building your own microphone for information on building a quality microphone for under 5 dollars.Note that your own custom microphone will not be calibrated, so expect a ±3-4dB error vs. ±1dB for a calibrated microphone.Most of this error is above 4kHz and is a soft error. It will not cause lots of random narrow spikes in your tests, so it can be used to try to find any spikes in a response curve.It will not help in identifying speakers that gradually increase or decrease in SPL over a wide frequency range since that could be a result of the microphone itself.So what does this mean? With an uncalibrated microphone you can still design a series or parallel notch filter, but you should not add a contour network based on results from an uncalibrated microphone.If you still want to purchase a calibrated microphone, check out the combined calibrated microphone + software deal from True Audio.
Use a laptop for speaker testing if you have one. It will make things a lot easier. Plug your microphone into the microphone input jack on your computer.On a computer this is typically a 1/8' (3.5mm) mono plug.You will need an adapter if your microphone has a 1/4' or a standard professional microphone connector.Typically, a professional microphone will have the jack shown on the right, and the microphone cable will convert from that 3 pin connector to a 1/4' plug.You then need a 1/4' to 1/8' adapter which can be easily found online or at an electronics store.
This is what the jack looks like on the computer. The jack on the computer may be pink.
Place the microphone in front of the speaker. If you are testing a single driver, then place the microphone right in front of the driver, centered on the cone and aimed directly at the driver.Shotgun microphones work well for these tests. Place the speaker off the floor and away from any walls (including behind the speaker). This will reduce reflections that could impact the test.
If you are testing a speaker box with multiple drivers then you will need to place the microphone a couple of feet from the speaker - or a couple of yards away if using a shotgun microphone.This is necessary so that the microphone can pick up the signal from all of the drivers.
Your other option is to setup an in-room listening test. Place the speakers where you want to have them permanently located in your roomand place the microphone in your most likely listening position. Do not use a shotgun microphone for this type of test since you actuallywant to account for the in-room reflections in the test. This type of test is used to find the ideal speaker location, height, and angle for your room.This test can be done with speakers you have constructed or ones you buy off the shelf.
In any case, you should fashion some type of microphone holder for your tests. Do not try to hold the microphone in place with your hand.You will not be able to hold it steady enough. This might be OK for the subwoofer frequencies, but it will have a dramatic impact on the higher frequencies.You don't need to buy a real microphone stand. Use any type of clip/clamp that will hold it in place.
Next, plug a 1/8' (3.5mm) to RCA Adapter into the line-out jack in the computer. This will be a green jack on the computer.Then run RCA/Composite cables from the adapter to your stereo receiver. If your computer has a digital output (either optical or coaxial) then use that connector instead.You could also use a DisplayPort or HDMI connector if your stereo supports it. These digital cables carry both audio and video.
Finally, hook the stereo up to the speakers that you are testing. Make sure that you don't have any active crossovers or equalizers enabled if you are using a receiver.For example, any modes like Hall, Stadium, Movie, or Game will affect the speaker output. Your receiver may also automatically enable a high pass filterif you are using a subwoofer. Disconnect any subwoofer and turn off any filters in the receiver before starting your testing.Note: If you need that high pass filter because your speakers aren't full range, then leave it in place. Also, if you are performing an in-room listening test to determine speaker positioning,then you should connect and run all speakers (including the subwoofer with the active crossover) as you would normally.
Now for the software. For free software I recommend AUDio MEasurement System (AUDMES).On the paid side, TrueRTA from True Audio or ETF Acoustic.TrueRTA is cheap enough and very popular. There is a free version of TrueRTA, but it can only take 1 measurement per dB which is not adequate for real speaker testing.ETF has a free demo that should do everything you need.
All of these tools generate a series of tones from your computer and then measure the volume (SPL) of those tones using the microphone.They then display the results in a nice chart so that you can easily see any spikes and dips in the frequency response.With every tool, you should first raise the volume of your computer and lower the volume of both the stereo/receiver.You want the volume during the test to be loud (better signal to noise ratio), but not more than your speaker drivers or stereo can handle.Start low and then raise the volume once you are comfortable.Note: In my own testing, I've seen higher noise levels when the computer volume was lower and the stereo was higher - even though the net effect was the same volume.
Also, most tools detect your input (microphone) and output (speakers) at startup. It is best to plug in everything before starting the program.
How to use AUDMES: This tool is very easy to use. It should automatically detect your sound card and your input/output channels on start.If not, you can select/change your Input/Output devices from the Tools->Select Sound Card menu option.To begin your test, select the Frequency Response tab from the bottom of the window and then click Start.It takes about a minute to run each test.
How to use TrueRTA: There are 4 levels of TrueRTA. The highest level (and most expensive version) allows for 24 measurements per octave.The program will default to 1 measurement per octave regardless of what version you purchase, so the first thing you should do is change the RTA Resolution on the right side of the screen to whatever level you have purchased.Click the Quick Sweep button on the bottom left of the screen and within a second you have a full frequency response chart.Note: In my testing, I changed the Ampl. (Amplitude / Computer Volume) on the right side of the screen from -10dB to 0dB.
How to use ETF: From the top menu, select File -> New Measurement -> Normal Transfer Function.On the popup window, check the Sweep radio button in the Measurement area.From the top right of the popup window, click Level Check to check the sound level. If the sound level is green, then click Start Test.The program will not produce two quick frequency sweeps - One for the Left speaker and one for Right. If only one speaker is connected then you will hear only one sweep.Since you only have a single mono microphone, you will get only one response curve. Click OK at the top to get your frequency response curve.Enlarge the new window with the chart to make it readable. Check the Linear Frequency Response icon at the bottom to get the right chart.
Here are some sample frequency response charts from TrueRTA using a B&W 602 with a custom wired Panasonic WM-61A Microphone without a shotgun tube.For the first three charts, the microphone was mounted within 1' of the tweeter, woofer, or port of the speaker. I tested the port just to see the effect it was having on the system overall.Notice the nice flat response on the tweeter measurement. Not bad for a $1.90 microphone cartridge.
One Inch from Tweeter
One Inch from Woofer
One Inch from Port
In the fourth test the microphone was placed 6' from the speaker centered between the tweeter and woofer. For the final test, the microphone was 1 meter away, still centered on the tweeter and woofer.
Six Inches centered on Tweeter & Woofer
Free Speaker Testing Software
One Meter centered on Tweeter & Woofer
Speaker Testing Software Program
Since I don't have a proper sound room to perform testing, the in room reflections are worse as the microphone is further away from the speaker.The measurement from 6' is pretty good, but since the port is below the woofer the microphone isn't able to measure the deep bass (as seen in the 3rd chart) that comes from the port.
I don't see anything in any of these tests that would warrant any additional modifications to the crossover. Given this is an off-the-shelf speaker that is to be expected.Here are some things to look for in speaker testing:
Speaker Testing Software
- A large drop (~20dB) at a crossover point would indicate that the drivers are canceling each other out. Try reversing polarity (swap + & -) on one of the drivers to see if the dip goes away. If the response is louder at the crossover point with the polarity reversed then it should probably be reversed.
- Any other narrow spike (~10dB) (Ex: at the resonant frequency of a tweeter) might need to be fixed using a Series Notch Filter.
- A wide dB gain in the response that corresponds to a single driver's output could be caused by that driver having a higher sensitivity than the others. This can be resolved with a Driver Attenuation Circuit / L-Pad.
- Other dB gains over a wide area that are not attributed to different driver sensitivities can be resolved using a Parallel Notch Filter.
- A subwoofer with a declining response curve (caused by rising impedance of the large coil in the crossover at higher frequencies) can be fixed with an Impedance Equalization Circuit.
- A driver with a rising response curve can be resolved with a Contour Network.