What comb effect are you referring to? The one due to stereo speaker playback?
I don't see how the use of a tube introduces a comb effect in and of itself.
Unless you are referring to the HRTF, that is comprised of many things, including comb effects.
In that case, you do not want to get rid of it.
It is part of the binaural cues that get encoded in the recording and that you need to retrieve during playback to be able to localize and recognize sounds correctly.
It looks like Chris might be more expert on this specific question, though.
He seems to have good equipment to measure both amplitude and phase responses.
Expert? Never.
I was into HiFi for years, and then got into live sound before deciding to try and make a living out of it. Somewhere in the middle, I got myself a Physics degree.
While the software I'm using (Room EQ Wizard, it's free) is pretty powerful, I can only measure phase, not alter it.
I'll do a couple more measurements in the way you've suggested, EQ the result flat and let you know how it goes.
Chris
Chris,
While waiting on your measurements, and gathering info for my single driver speaker project, I found myself in a catch 22 situation I'm going to submit for your consideration, given that you seem to have the mathematical background to understand.
It appears that there is no way of knowing a calibration microphone's phase response.
Some (very few) publish it based on the assumption that the microphone is a minimum phase device and applying the Hilbert transform from the amplitude response, but that's a big assumption.
The majority of makers don't even bother to publish it.
So, my question is, are you measuring the phase response of the tube or the phase response of your measurement microphone? Or most likely a combination of the two (plus the source's phase response)?
Food for thought...
While waiting on your measurements, and gathering info for my single driver speaker project, I found myself in a catch 22 situation I'm going to submit for your consideration, given that you seem to have the mathematical background to understand.
It appears that there is no way of knowing a calibration microphone's phase response.
Some (very few) publish it based on the assumption that the microphone is a minimum phase device and applying the Hilbert transform from the amplitude response, but that's a big assumption.
The majority of makers don't even bother to publish it.
So, my question is, are you measuring the phase response of the tube or the phase response of your measurement microphone? Or most likely a combination of the two (plus the source's phase response)?
Food for thought...
In case someone is interested I opened up this can of worms here
http://www.diyaudio.com/forums/equi...t-microphones-phase-response-calibration.html
http://www.diyaudio.com/forums/equi...t-microphones-phase-response-calibration.html
Hi Sax,
I've just been through a load of paperwork, and will be moving house over the next week or so. It's an exciting and busy time for me, but audio projects (apart from gigs, which pay the bills) will be on hold I'm afraid.
Regarding microphone phase,
You're certainly measuring the phase (and frequency) response of the head + ears + canals + mics + source.
What you can do is take the mic and measure the source directly. Then you can use that data to derive the phase and amplitude response of the head + ears + canals.
Seperating things further gets difficult - you're always going to need a source and a microphone.
If you choose the source carefully, I think it should be possible to get a source that's phase linear through a useful range. Note that we don't need much SPL to get a reading. A 0.5" metal dome tweeter would likely be what I'd use. The diaphragm would be acting as if it were perfectly rigid throughout the audio band, and therefore the sound produced ought to follow the voicecoil signals very closely. There is, of course, the spring-mass resonance of the tweeter, and the associated rolloff lower down. I suspect it's possible to account for those in the measurements. The alternative would be to use a bigger driver to go below 1kHz or so.
Chris
I've just been through a load of paperwork, and will be moving house over the next week or so. It's an exciting and busy time for me, but audio projects (apart from gigs, which pay the bills) will be on hold I'm afraid.
Regarding microphone phase,
You're certainly measuring the phase (and frequency) response of the head + ears + canals + mics + source.
What you can do is take the mic and measure the source directly. Then you can use that data to derive the phase and amplitude response of the head + ears + canals.
Seperating things further gets difficult - you're always going to need a source and a microphone.
If you choose the source carefully, I think it should be possible to get a source that's phase linear through a useful range. Note that we don't need much SPL to get a reading. A 0.5" metal dome tweeter would likely be what I'd use. The diaphragm would be acting as if it were perfectly rigid throughout the audio band, and therefore the sound produced ought to follow the voicecoil signals very closely. There is, of course, the spring-mass resonance of the tweeter, and the associated rolloff lower down. I suspect it's possible to account for those in the measurements. The alternative would be to use a bigger driver to go below 1kHz or so.
Chris
I wouldn't have suspected that of being binaural. Wolfson distributed a 24/96 cut from that album for free download (very slow link at bottom of article here: A nice and free 24/96 flac Chesky collection - Blog - Archphile). Over my speakers it has little to none of the spaciousness obvious on other binaural downloads so I never thought to try it on headphones.
It's still an excellent recording and a go-to for assessing equipment but only has a slight sense of the opening guitar being left of left. It's nowhere near the experience of some of the naturalist or air show recordings in the pile that can wrap 90 degrees either side of me. The bulk of listening was on Apogee Centaur Minors and the Technics SB-C700, the latter a flat concentric as close as a 2-way gets to a single driver full range. I'm sure it got time on my Jordans before one cabinet hit the floor and sheared a magnet off. I don't recall it standing out as any different.
I listened to your cuts directly off Dropbox, are they still available? Very spacious on headphones, didn't hear them over speakers.
I listened to your cuts directly off Dropbox, are they still available? Very spacious on headphones, didn't hear them over speakers.
I unshared the Dropbox folder as I don't want to share my recordings publicly, but if you PM me and give me your email address I will send you another link.
Incidentally, when you say the guitar left of left, do you mean that you expect it at 9 o'clock? I hear it in front center, with the voice. In fact, she plays the guitar, I believe.
Or are you referring to the double bass?
Incidentally, when you say the guitar left of left, do you mean that you expect it at 9 o'clock? I hear it in front center, with the voice. In fact, she plays the guitar, I believe.
Or are you referring to the double bass?
Hi all,
Reviving this now I have a little more time to work on it between gigs.
To get myself back up to speed I did this:
- Put a measurement mic up in front of a test speaker (this time, a Bose MusicMonitor - 2" full-range system covering ~70Hz-16kHz), and derived a calibration curve, which was applied to all future measurements. Any response anomalies in the speakers themselves are compensated for.
- Put Ed on a stand, run a sweep from the test speaker with the head around 12" away. Head was at 45 degrees, ear was on-axis with the speaker.
- Repeat for the other ear
- Average the two curves.
- Apply EQ to the mic feed to flatten down the spectacular bump in the response at 3-5kHz. I also knocked down the region around 16kHz a touch. The final response is pretty flat, according to the mics inside the head.
Listening to the feed from the mics sounds pretty good. Even with some fairly nice headphones (Shure SRH840), I think there's more to be had, though. The sound just isn't quite as convincing as it is with the example videos on YouTube.
Chris
Reviving this now I have a little more time to work on it between gigs.
To get myself back up to speed I did this:
- Put a measurement mic up in front of a test speaker (this time, a Bose MusicMonitor - 2" full-range system covering ~70Hz-16kHz), and derived a calibration curve, which was applied to all future measurements. Any response anomalies in the speakers themselves are compensated for.
- Put Ed on a stand, run a sweep from the test speaker with the head around 12" away. Head was at 45 degrees, ear was on-axis with the speaker.
- Repeat for the other ear
- Average the two curves.
- Apply EQ to the mic feed to flatten down the spectacular bump in the response at 3-5kHz. I also knocked down the region around 16kHz a touch. The final response is pretty flat, according to the mics inside the head.
Listening to the feed from the mics sounds pretty good. Even with some fairly nice headphones (Shure SRH840), I think there's more to be had, though. The sound just isn't quite as convincing as it is with the example videos on YouTube.
Chris
Hi Chris.
The procedure you described sounds right. What kind of ears did you use on Ed? Did you try at least plastic tubes for ear canals?
Also, the equalization will play an important role on the final sound quality.
Your choice of a single driver speaker is good, although more extension in the bass region would be nice.
Also, the averaging of the curves could be bypassed, and you could try to equalize each channel independently.
Is the equalization done by a matching EQ plugin or manually, as I seem to gather? A plugin would be more accurate.
But anyway, you seem to be on the right track.
Here are two links to a recording session I did just a few days ago.
https://www.youtube.com/watch?v=b1mtKjdgQi0
https://www.youtube.com/watch?v=yr84sneJcJk
The microphone was put quite far for video capturing reasons (20-23 ft), and the customer wanted a nice 'blended' sound, at the expense of a little separation (which I would have preferred).
But I think there is a good sense of space, and it might be useful for you to compare with your own recordings and get some ideas on what to try next.
The procedure you described sounds right. What kind of ears did you use on Ed? Did you try at least plastic tubes for ear canals?
Also, the equalization will play an important role on the final sound quality.
Your choice of a single driver speaker is good, although more extension in the bass region would be nice.
Also, the averaging of the curves could be bypassed, and you could try to equalize each channel independently.
Is the equalization done by a matching EQ plugin or manually, as I seem to gather? A plugin would be more accurate.
But anyway, you seem to be on the right track.
Here are two links to a recording session I did just a few days ago.
https://www.youtube.com/watch?v=b1mtKjdgQi0
https://www.youtube.com/watch?v=yr84sneJcJk
The microphone was put quite far for video capturing reasons (20-23 ft), and the customer wanted a nice 'blended' sound, at the expense of a little separation (which I would have preferred).
But I think there is a good sense of space, and it might be useful for you to compare with your own recordings and get some ideas on what to try next.
Hi Sax,
The EQ I use is built-in on the nearest device I have, usually a digital mixing desk. There's also the option to add a 31-band graphic EQ into the mix, which I might try out for the broader strokes.
I run the sweeps with REW, play around with simulated EQ until I get something good, apply that EQ at the desk and then run the sweeps again to confirm that what I simulated is what has been applied.
There are some rubber tubes a little under 1" long going from the pinnae to the mic capsules.
I can test for bass extension - plenty of subwoofers around here. I think the midrange is still where I'm finding Ed lacking, though, so I'd like to get that right first. I suspect the low-frequency response will be easier to sort out since the head itself won't be affecting things much down there, so it's just the rolloff of the mics that needs compensating for.
Thanks for the recording links, I'll have a listen.
Chris
The EQ I use is built-in on the nearest device I have, usually a digital mixing desk. There's also the option to add a 31-band graphic EQ into the mix, which I might try out for the broader strokes.
I run the sweeps with REW, play around with simulated EQ until I get something good, apply that EQ at the desk and then run the sweeps again to confirm that what I simulated is what has been applied.
There are some rubber tubes a little under 1" long going from the pinnae to the mic capsules.
I can test for bass extension - plenty of subwoofers around here. I think the midrange is still where I'm finding Ed lacking, though, so I'd like to get that right first. I suspect the low-frequency response will be easier to sort out since the head itself won't be affecting things much down there, so it's just the rolloff of the mics that needs compensating for.
Thanks for the recording links, I'll have a listen.
Chris
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