Bob, if you decide to give a headphone amplifier talk, let me suggest a possible alternative to (or a possible accompaniment to) crossfeed: stereo width expansion. That's merely
where (0 < alpha < 1). Normal stereo with no width expansion corresponds to alpha=1. Otherwise each earpiece gets its input signal MINUS a portion of the other earpiece signal. Amusingly, alpha=0 corresponds to completely swapping the two channels. So you can continuously dial between Channels_Swapped (alpha=0), pure mono (alpha=0.5), and pure stereo (alpha=1.0)
This idea got QUITE a lot of favorable press, when BSG Technologies sold effects boxes that provided it: (review in Stereophile)
Maybe you might have opinions and observations about using it with headphones? If so that might be two or three fun slides in your BAF presentation.
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RightOut = [alpha * RightIn] - [(1-alpha) * LeftIn]
LeftOut = [alpha * LeftIn] - [(1-alpha) * RightIn]
LeftOut = [alpha * LeftIn] - [(1-alpha) * RightIn]
where (0 < alpha < 1). Normal stereo with no width expansion corresponds to alpha=1. Otherwise each earpiece gets its input signal MINUS a portion of the other earpiece signal. Amusingly, alpha=0 corresponds to completely swapping the two channels. So you can continuously dial between Channels_Swapped (alpha=0), pure mono (alpha=0.5), and pure stereo (alpha=1.0)
This idea got QUITE a lot of favorable press, when BSG Technologies sold effects boxes that provided it: (review in Stereophile)
Maybe you might have opinions and observations about using it with headphones? If so that might be two or three fun slides in your BAF presentation.
_
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Hi Mark,
This definitely fits into such a discussion; in fact, this is a form of crossfeed.
In the more general case, the crossfeed amplitude is a function of frequency and frequency response slope, in recognition of intra-aural delay and frequency response. In some cases, there may even be electronic delay introduced into the crossfeed path by means of all-pass delay circuits.
In the very early days of FM stereo, I had an EICO FM stereo autodapter to connect to my monophonic EICO HFT-90 FM tuner. The tuner had a separate wideband output without de-emphasis in anticipation of the availability of FM stereo. The multiplex adapter (implemented with tubes) had a conspicuous knob on the front panel labeled "separation" that controlled the mix of L+R and L-R to achieve optimum separation. This is a little reminiscent of the approach you described. Of course, this was in the context of loudspeaker listening as opposed to headphone listening.
Cheers,
Bob
This definitely fits into such a discussion; in fact, this is a form of crossfeed.
In the more general case, the crossfeed amplitude is a function of frequency and frequency response slope, in recognition of intra-aural delay and frequency response. In some cases, there may even be electronic delay introduced into the crossfeed path by means of all-pass delay circuits.
In the very early days of FM stereo, I had an EICO FM stereo autodapter to connect to my monophonic EICO HFT-90 FM tuner. The tuner had a separate wideband output without de-emphasis in anticipation of the availability of FM stereo. The multiplex adapter (implemented with tubes) had a conspicuous knob on the front panel labeled "separation" that controlled the mix of L+R and L-R to achieve optimum separation. This is a little reminiscent of the approach you described. Of course, this was in the context of loudspeaker listening as opposed to headphone listening.
Cheers,
Bob
Bob,
I really like the idea of a headphone amplification & crossfeed talk. Add my vote in favor!
On the headphone subject, I see lots of misconceptions floating around about how much power is needed… “high impedance headphones are hard to drive” etc. (actually not - they just need more voltage swing, which can be a challenge in a portable device with limited supply voltage)… appropriate selection of gain structure (perhaps it’s just me, but many headphone amp designs seem to have too much gain, given modern source component output levels, headphone sensitivities, and sensible listening SPL) … noise, output impedance, headroom considerations … these seem like subjects worthy of some demystification, and fertile ground for discussion.
Crossfeed is a fun topic too… somewhat tangential, but I have found it insightful over the years to study how stereo width perception is achieved in the studio with mic techniques (XY, Blumlein, M+S, ORTF, binaural, etc.) and in the mix… it’s generally all about phase (or delay), level, and frequency response shaping of the left-right stereo bleed. Modern HRTF techniques have brought in a whole new ball of yarn to play with.
I really like the idea of a headphone amplification & crossfeed talk. Add my vote in favor!
On the headphone subject, I see lots of misconceptions floating around about how much power is needed… “high impedance headphones are hard to drive” etc. (actually not - they just need more voltage swing, which can be a challenge in a portable device with limited supply voltage)… appropriate selection of gain structure (perhaps it’s just me, but many headphone amp designs seem to have too much gain, given modern source component output levels, headphone sensitivities, and sensible listening SPL) … noise, output impedance, headroom considerations … these seem like subjects worthy of some demystification, and fertile ground for discussion.
Crossfeed is a fun topic too… somewhat tangential, but I have found it insightful over the years to study how stereo width perception is achieved in the studio with mic techniques (XY, Blumlein, M+S, ORTF, binaural, etc.) and in the mix… it’s generally all about phase (or delay), level, and frequency response shaping of the left-right stereo bleed. Modern HRTF techniques have brought in a whole new ball of yarn to play with.
Just FYI the X Long Now Foundation The Long Now Foundation - Fostering Long-Term Thinking has a bar The Interval at Long Now twenty steps away from our spot! Cocktails made with science and the best craft drinks we have ever had.
And the 10,000 year clock is interesting too.
Vince
And the 10,000 year clock is interesting too.
Vince
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I'd be interested in hearing more about that. I hope the talk will be videotaped.
I'm not likely to make it in person as the US in their infinite wisdom have decided that my particular vaccine cocktail isn't kosher. The border is also currently closed in the southbound direction so my attendance at RMAF is hanging by a thread.
Tom
Yes, it's me.
Looks like the Mods deleted my post of public health-based scientific facts and data.
I'm excited about going.
I've got the finishing touches on the RIAA stages I designed, and I'm working on another preamp for myself that runs 5691 and 5692 tubes, with vintage Simpson VU meters.
A few months back I bought a diy active 3 way crossover using tubes, which i drew a schematic for.
I'll probably bring that and see what sort of info I can gather on it before I proceed to clone it.
Not sure how much of the chico club is planning on going but if we get enough of us we could stack 5 of my "members only" preamps, and run every amp in the building off the output. Unlike last time they are now "finished" in an inch of Claro walnut. All 5 of them got wrapped in some extremely nice hardwood. Not veneered plywood mind you. 1" of real natural, local, burlwood. I cant wait to see what others have done with their abundance of free time.
I've got the finishing touches on the RIAA stages I designed, and I'm working on another preamp for myself that runs 5691 and 5692 tubes, with vintage Simpson VU meters.
A few months back I bought a diy active 3 way crossover using tubes, which i drew a schematic for.
I'll probably bring that and see what sort of info I can gather on it before I proceed to clone it.
Not sure how much of the chico club is planning on going but if we get enough of us we could stack 5 of my "members only" preamps, and run every amp in the building off the output. Unlike last time they are now "finished" in an inch of Claro walnut. All 5 of them got wrapped in some extremely nice hardwood. Not veneered plywood mind you. 1" of real natural, local, burlwood. I cant wait to see what others have done with their abundance of free time.