how can i find out the lowest frequency in a song?

[theoilweapon]

Hi all, I recently got a VTF-2 and I love it. LOVE IT. I was mostly using it is maximum extension mode, but on some tracks maximum output mode sounds much louder/better. I read in the setup guide that if the program doesn't have any frequencies below 32Hz, maximum output mode will tax the system less. I use the sub through a receiver connected to my computer with USB cable, or with a regular CD player. I just don't want to put extra strain on the subwoofer, that might shorten it's lifespan, when i don't even need to.

Q: Is there a piece of hardware of software that can determine the lowest frequency of a music or movie program (that is relatively cheap)?

Q: Would a spectrum analyzer be useful? What brands might i consider?

[theoilweapon]

okay i did some research. I found a software spectrum analyzer at True Audio (http://www.trueaudio.com). The problem is it needs to interface with a microphone. Is there anything that will just tell you the spectrum directly from the source?

[Retread]

Originally posted by theoilweapon
okay i did some research. I found a software spectrum analyzer at True Audio (http://www.trueaudio.com). The problem is it needs to interface with a microphone. Is there anything that will just tell you the spectrum directly from the source?

I was interested in that sort of thing myself, and instantly ordered the product when I saw your post. I got the Level 4, which is roughly $100. One downloads the free demo and then enters the activation code they email.

I've loaded the program and tinkered briefly. Lots of functionality, which means some complexity. I'd suggest printing off the help files for reading. Point to each chapter and print. It will print all the pages in that chapter.

There are procedures for calibrating out variances in the computer audio card -- once done, no need to do it again. There is also a procedure for calibrating out variances in the microphone -- once done, no need to do it again. I have the Radio Shack SPL meter, which has an output that can be plugged into the computer audio card. Since the variances are known, I should be able to use it to good effect.

There are multiple modes that can be used for test:

(1) sinewave - oscilloscope. One can input a sine wave of chosen frequency and amplitude, and see the resultant sine wave in oscilloscope mode.

(2) sinewave - spectrum. One can input a sine wave of chosen frequency and amplitude, and see the resultant spectrum in spectrum analyzer mode. The help files have 3rd harmonic distortion dB levels.

(3) pink noise and chirp - spectrum. One can input either pink noise or chirp and see the resultant spectrum. With both modes, the resultant spectrum should be flat. Any deviations from flat will indicate some speaker frequency response variance. Chirp mode is interesting. The system used Fast Fourier Transform to generate a sliding sine wave from bottom to top of the frequency range. One chirp gives the complete, noise-free frequency response of the system. As a side note, one would have to measure frequency response at several locations and average to level out room variances.

(4) music - spectrum. One can play music and display the spectrum. This will identify the frequency components and levels of the music.

Again, thanks for the tip. This is precisely the tool I have been yearning for.

[Retread]

If you plug your preamp into the line level input of the computer audio card, it will do spectrum for the music.

[theoilweapon]

Originally posted by Retread
If you plug your preamp into the line level input of the computer audio card, it will do spectrum for the music.

I'm glad I helped you out! There were quite a few online. The hardware versions I found were much more flexible than I need, not to mention thousands of dollars. And that was the best looking software one I found. I can hook my stereo into my laptop easily enough, but I really want one that analyzes the spectrum as the music program is playing. The search continues. Good feature overview ;)

[Retread]

"I really want one that analyzes the spectrum as the music program is playing."

I plugged my player directly into the line input of my laptop and started "Pictures At an Exhibition," since that piece has a lot of bounce and lows. Set Spectrum Analyzer Mode, Real Time Analyzer, Bandwidth 10Hz-20kHz, Bars display. It shows the real time content of the music in bouncing bars in frequency bands. Turn off the bars, and it gives a line representing the tops of the bars. Turn on Peak Hold and it provides a relatively static display in bars of the maximum level in each band to the point at which the music has played.

I think it will do pretty much anything one can think of and have the patience to ferret out. Most things are fairly simple and intuitive, though.

I really like this software!

[theoilweapon]

Perfect!!! That takes care of that. I love forums... :cool:

[Sasha_G]

I haven't checked out True Audio yet, but Spectrum Lab lets you use the internal audio from the soundcard without the need for looping back with an extra cable.

It is free.

More info:
http://hsuresearch.com/forum/showthread.php?postid=1521&highlight=Speclab#post1521

[theoilweapon]

Thanks Sasha that is exactly what i was looking for. :D

[John Murphy]

Hello!

I just want to point out that TrueRTA CAN analyze the internal audio of the PC. It can analyze any available source by selecting that source at the Windows Record mixer. So you can analyze the sound cards Mic In, Line In, CD In or even the WAV signal internal to the PC. For quick and dirty analysis just plug a simple multimedia mic directly into the PC's Mic In and select Mic-In at the Record Mixer. To use an external calibrated mic connect the mic preamp output to the PC's Line-In and select Line-In at the Record Mixer. To directly analyze the audio from a CD playing within the PC just select the CD input at the Record Mixer.

Regards,

John Murphy
True Audio
www.trueaudio.com Get your free version of TrueRTA!

[Sasha_G]

John,

Thank you for posting! Very nice software, by the way. I tried it recently to measure the bass on Black Hawk Down on my laptop. No loop back was required, as it used the output from the sound card produced by PowerDVD. There are some advantages in your software over the free software I mentioned, including things that we need over at HSU such as "peak hold".

The reasonable price makes your software a good choice for people who want to do test measurements of speaker frequency response or their room response at various positions.

Now, if we only had the option to do speaker distortion measurements for a low price... that could enable a whole new breed of smart people on the internet with tools in hand to look beyond marketing and make informed decisions!

[Retread]

Now, if we only had the option to do speaker distortion measurements for a low price... that could enable a whole new breed of smart people on the internet with tools in hand to look beyond marketing and make informed decisions!

TrueRTA will generate low-distortion sine waves at the frequency of your choice. Apply the sine wave to the amp, connect a calibrated mic to the computer, and measure harmonic distortion in the spectrum analyzer mode.

[Sasha_G]

But after looking at the software, I didn't see an automatic calculation. I guess its possible if you do some manual calculations.

It seems like it would be such an easy addition to program in...One can wish.

[Retread]

But after looking at the software, I didn't see an automatic calculation. I guess its possible if you do some manual calculations.

It seems like it would be such an easy addition to program in...One can wish.

True. Pending that, it shouldn't be too tough. I was about to do distortion measurements on my system when my sub's RCA jack lost its ground. The software provides fundamental and harmonic magnitudes in dB. I was planning the enter the frequency, fundamental, and harmonic dB magnitudes into an Excel spreadsheet and set up calculations that would subtract the harmonic from the fundamental, do the 20Log conversion to voltage ratios, compute percentage distortion, and then plot the result.

[Sasha_G]

I was planning the enter the frequency, fundamental, and harmonic dB magnitudes into an Excel spreadsheet and set up calculations that would subtract the harmonic from the fundamental, do the 20Log conversion to voltage ratios, compute percentage distortion, and then plot the result.

That sounds great! Let me know when you do that.

[Sasha_G]

Mics

If anyone else wants to do measurements, I've been told that the Behringer ECM8000 (http://www.behringer.com/ECM8000/index.cfm?lang=ENG) is a good measurement mic on a budget, and the price starts at $50. We haven't tested it yet at HSU though.

$50 at ZzSounds http://www.zzounds.com/item--BEHECM8000
$50 at PartsExpress http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=248-625
$50 at Musician's Friend http://www.musiciansfriend.com/srs7/sid=040617215707004047031186204151/g=home/search/detail/base_pid/270400/

Mic Pre-Amps and Sound Cards

Not to spoil the fun, but Dr. Hsu recommends taking distortion measurements outside. This might mean using a laptop.

If you do use a laptop, we recommend upgrading the sound card on the laptop. Laptops often have the worse sound cards known to man. The M-Audio Mobilepre USB (http://www.maudio.co.uk/index.php?do=products.main&ID=8eb1a9920df341303f81bca7ff458be3) is a solution which also includes a pre-amp.It is $150 at Musician's Friend (http://www.musiciansfriend.com/srs7/sid=040617215707004047031186204151/g=home/search/detail/base_id/103189)

-or-

If you can use your PC outside, then the equipment might be different. If your sound card is good, you might only need a preamp for the mic, such as the $70 Behringer Eurorack UB1002 Mixer (http://www.musiciansfriend.com/srs7/sid=040617215707004047031186204151/g=home/search/detail/base_id/88619). If your soundcard isn't that hot, then you can get a new one at newegg.com (http://www.newegg.com/app/ViewProductDesc.asp?description=29-102-162&depa=0) . Newegg also has professional soundcards with built in pre-amps (http://www.newegg.com/app/viewProductDesc.asp?description=29-121-106&depa=0).

[Retread]

"If anyone else wants to do measurements, I've been told that the Behringer ECM8000 is a good measurement mic on a budget, and the price starts at $50. We haven't tested it yet at HSU though."

I have that microphone, and it is pretty good. However, it requires a separate device to provide phantom power. I have the Behringer Shark, which requires AC power and wouldn't be a very good solution for outdoor testing unless you run a long extension cord.