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#31
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Stereo INPUT on laptop?
Charlie wrote:
On 6/29/2015 8:12 AM, Big_Al wrote: . . .winston wrote on 6/28/2015 9:35 PM: Big_Al wrote: I know the only input I have is a mono microphone jack. And all the searching I've done for stereo audio "input" does not seem to grab the concept of input in the search and I find lots of USB audio dongles that have stereo outputs and one mono jack input. As I see it they would be used if my current audio hardware broke and USB still functioned. Does anyone know of a way to get stereo input on a laptop or does a laptop actually have stereo in circuitry if I got the data in? Using a Dell Inspiron N5110. Sure the device is not Mono output via speaker but Stereo out via headphone connector ? Since it's only one jack each (in / out) I know the headphones are stereo, and doubt they would power speakers. The input (mic) is the only item I think is mono. I now recall trying audacity and I can't get it to show stereo and any other microphone setting in windows are showing mono. And since I've got other options I'm not fighting it. Some have suggested the ports may be swappable and if so that might work. All I need now is time and testing. Actually, many of the current headphones contain speakers. The impedance may be higher than that usual for the usual speakers. Even if the laptop contains an audio chip-set that is full stereo, The mic jack may be mono,and wired to supply both channels. Why? you would have to ask the mfr. It does get even stranger! I had a circa 1996 model laptop that had built in stereo mikes, and yet the external mic jack was mono. You had to use line in if you wanted to record in stereo. This is an artifact of the AC'97 generation of solutions. The problem starts, with the IC package. The manufacturers get a "fixation" with 40 pin PLCC or the like. They try and squeeze as much crap as possible, into the 40 pins. Some features "fall off the table" as a result. On the old AC'97 chips, you could indeed see stereo input for one interface instance, and mono for a second one. And there was then, no way to fix it. AC'97 jacks were not retaskable. And some 1x3 jack stacks on the back of computers, used outboard circuitry to select channels off the audio chip, and connect them to the 1x3. The 1x3 could run 5.1 output and no inputs. Or it could run MicIn/LineIn/LineOut, and the multiplexing logic made it happen. Just a mess of a circuit. But at least it was well documented. I could find app notes explaining how it all works. HDAudio attempts to fix some of that. The ports are more uniform. They can switch roles internally, using internal configuration options. The ports have "jack sensing", and apparently can tell the difference between a 10K amp input and a 32 ohm headset. Or can sense (somehow), that an electret microphone is connected. The HDAudio spec specifies side contacts in the jacks, to sense "presence". But modern chips might be cross-licensing AC impedance sensing from one of the better companies, and that's how they can detect I/O type and put up a dialog box to that effect. It's the "more uniform nature" of HDAudio that makes it better. No need for silly outboard multiplexing logic. No stereo on this and mono on that. The ports are supposed to be more uniform. The OPs HDAudio chip is a bit different, in that it has high power audio amps included, which kinda spoils the retasking features a bit. But the remainder of the 5 stereo ports, can be retasked a bit. Some of those ports are better than others. One thing they haven't fixed, is the control panel. Given the uniformity of the audio output channels, it should be possible to switch any output jack "left" and "right". The control panel only allows "Center/Sub" to be switched, and no other jacks are shown. But I see no reason why this could not be done. And it would be more in keeping with the "we can fix anything" nature of HDAudio. 92HD87 http://i58.tinypic.com/qrlm5k.gif http://i59.tinypic.com/15fnj4o.gif Paul |
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#32
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Stereo INPUT on laptop?
In message , Paul writes
HDAudio attempts to fix some of that. The ports are more uniform. They can switch roles internally, using internal configuration options. The ports have "jack sensing", and apparently can tell the difference between a 10K amp input and a 32 ohm headset. Or can sense (somehow), that an electret microphone is connected. The HDAudio spec specifies side contacts in the jacks, to sense "presence". But modern chips might be cross-licensing AC impedance sensing from one of the better companies, and that's how they can detect I/O type and put up a dialog box to that effect. In practice I have never seen this actually work. My current low-end Thinkpad just pops up a banner saying "Information. You just plugged a device into the audio jack" whichever jack I plug things into and the Mic stays as a Mic In and the output stays as an output. I had an older Thinkpad that somehow sensed mono Mic or stereo Line-in on the input jack. It will have been pre-HDAudio. Many machines have a separate audio control separate from the Windows Mixer. On an Acer machine that I had, the two controls didn't follow each other, hence chaos. I think few computer designers have a clue about audio, or are told it's not important. -- Bill |
#33
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Stereo INPUT on laptop?
On 6/28/2015 1:37 PM, Stormin' Norman wrote:
On Sun, 28 Jun 2015 13:28:46 -0400, Neil wrote: On 6/28/2015 9:02 AM, Big_Al wrote: I know the only input I have is a mono microphone jack. And all the searching I've done for stereo audio "input" does not seem to grab the concept of input in the search and I find lots of USB audio dongles that have stereo outputs and one mono jack input. As I see it they would be used if my current audio hardware broke and USB still functioned. Does anyone know of a way to get stereo input on a laptop or does a laptop actually have stereo in circuitry if I got the data in? Using a Dell Inspiron N5110. If you find that your mic input is not stereo, and you don't need the complexity of the M-Audio device that was suggested by Keith, there are a slew of simple units available, like: http://www.amazon.com/Syba-SD-CM-UAU...udio+interface According to the manufacturer, the mic input on the above unit is mono. See: http://www.sybausa.com/productInfo.php?iid=248 Wow. My bad, consistent with my bad last couple of weeks! 8-( Fortunately, these inexpensive interfaces aren't rare. http://www.fullcompass.com/product/3...0lgQod 1qUMUw -- Best regards, Neil |
#34
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Stereo INPUT on laptop?
Bill wrote:
In message , Paul writes HDAudio attempts to fix some of that. The ports are more uniform. They can switch roles internally, using internal configuration options. The ports have "jack sensing", and apparently can tell the difference between a 10K amp input and a 32 ohm headset. Or can sense (somehow), that an electret microphone is connected. The HDAudio spec specifies side contacts in the jacks, to sense "presence". But modern chips might be cross-licensing AC impedance sensing from one of the better companies, and that's how they can detect I/O type and put up a dialog box to that effect. In practice I have never seen this actually work. My current low-end Thinkpad just pops up a banner saying "Information. You just plugged a device into the audio jack" whichever jack I plug things into and the Mic stays as a Mic In and the output stays as an output. I had an older Thinkpad that somehow sensed mono Mic or stereo Line-in on the input jack. It will have been pre-HDAudio. Many machines have a separate audio control separate from the Windows Mixer. On an Acer machine that I had, the two controls didn't follow each other, hence chaos. I think few computer designers have a clue about audio, or are told it's not important. I have an app note with comments. I can't find the original link for some reason. IDT_STAC9200_APN_20120817.pdf ------------------------------ IMPLEMENTING UNIVERSAL JACKS ON HD AUDIO CODECS In order for operating systems to properly configure analog audio devices, based on their device type, Microsoft recommends that manufacturers design their devices to the following impedance criteria: * Passive speakers – 4 Ohm to 16 Ohm * Headset (speaker section) – 32 Ohm to 100 Ohm * Microphones – 400 Ohm to 1500 Ohm. * Powered speakers – 3000 Ohm to 12000 Ohm. Impedance Range 0 - 100 Headphones and unpowered speakers 400 – 1500 Microphones 3000 – 12000 Powered speakers and other line out devices Inaudible Test Signal IDT’s HDA codecs use a 24 kHz square wave, in a short burst, to sense device impedance. This frequency is high enough to be inaudible to the human ear. The basic sequence follows. Initial condition: Jack is empty. Port is configured as an input, VREF (if present) is forced to 0V. Plug inserted: SENSE_A or SENSE_B changes voltage, triggering an unsolicited response, as described in the High Definition Audio Bus Specification Rev 1.0. Get ready: Port is configured as an output (required to run Impedance Sense). Wait for charge-up: Wait long enough for DC-Blocking cap to charge. A good worst-case wait time (headphone port with a 47uF DC-Blocking cap and a line out load) is 2 seconds. Run Impedance Sense: Send 709 verb Wait for result: Test takes 2 ms to run. Wait for this much time to pass. Read Impedance Value: Send F09 verb and read response. If impedance is 7FFF FFFF, then result is not valid – wait and repeat. Timeout if valid response is never received. ******* Designers do take audio more seriously. One enthusiast motherboard, they highlight the "moat" or ground ring around the audio wiring, with red colorant. To show you they cared. And the machine I'm typing this on, has the HDAudio chip in a shielded housing. They routed the HDAudio digital signals through a PCI Express x1 connector, and the shielded module lives in that socket. Seems to work OK. I haven't torture tested it with Rightmark or anything. (Rightmark, done with loopback tests) http://images.anandtech.com/doci/9060/dynamics.png Paul |
#35
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Stereo INPUT on laptop?
Big_Al writted thus:
I know the only input I have is a mono microphone jack. And all the searching I've done for stereo audio "input" does not seem to grab the concept of input in the search and I find lots of USB audio dongles that have stereo outputs and one mono jack input. As I see it they would be used if my current audio hardware broke and USB still functioned. Does anyone know of a way to get stereo input on a laptop or does a laptop actually have stereo in circuitry if I got the data in? Using a Dell Inspiron N5110. Check the Sound settings, recording devices, microphone, properties, advanced. If you have the options of 2 channel settings, it is a stereo input. If you have only the options of 1 channel it is mono. Simples. Just check 'listen to this device' and choose where the input goes, speakers or whatever, uncheck any boost on the mic channel and plug in your ipod etc, then play your sounds... -- Free Dropbox: http://db.tt/aI6WBZ7w |
#36
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Stereo INPUT on laptop?
On 28/06/2015 14:16, Stormin' Norman wrote:
On Sun, 28 Jun 2015 09:02:44 -0400, Big_Al wrote: I know the only input I have is a mono microphone jack. And all the searching I've done for stereo audio "input" does not seem to grab the concept of input in the search and I find lots of USB audio dongles that have stereo outputs and one mono jack input. As I see it they would be used if my current audio hardware broke and USB still functioned. Does anyone know of a way to get stereo input on a laptop or does a laptop actually have stereo in circuitry if I got the data in? Using a Dell Inspiron N5110. Something like this? http://www.amazon.com/M-Audio-M-Trac...ywords=m-track This looks cheaper. http://www.ebay.com/itm/USB-6-Channe...e/141570512841 -- Brian Gregory (in the UK). To email me please remove all the letter vee from my email address. |
#37
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Stereo INPUT on laptop?
Big_Al wrote:
pjp wrote on 6/28/2015 8:57 PM: I will tell you from experience that if the material is "commercial" in nature rather than "private" recordings you're probably better off to just download the disk instead. I have about 200 or so 45rpm's and I was going to dub them but as a looked around I found I had about 150 of them and the other 50, I found about 45 of them. There are some like a Dick Clark special with 2-3 different songs on one side. And the ones I didn't have I wondered why I bought the 45 in the first place. The main reason I bought a PC 15+ years ago was to rip my vinyl. I had numerous 45s - not as many as you - and lots of LPs. Lots of work/time too but I'm glad i did it, many to most would not be commercially available. Speaking of time, it will require more than an hour of time for an hour of music...much more, depending upon the condition of the originals. After I finished with mine around 2000, I wrote a sort of "how to" entitled "dadiOH's dandies". I no longer have it posted anywhere but if you are interested, Shareup Networks made an html version of the original (doesn't have later and/or revisions). http://www.shareup.com/dadioh/ |
#38
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Stereo INPUT on laptop?
On Mon, 29 Jun 2015 14:16:41 -0400 "Paul" wrote in
article IMPLEMENTING UNIVERSAL JACKS ON HD AUDIO CODECS I'd never seen any of this - fascinating. I do a lot of audio work, but it's mostly processing of recordings made on other, dedicated digital recorders and have wrestled with Windows' weirdness regarding sound "cards" (be they PCI plug-ins or USB addons). I have come to conlude that external boxes attached via USB (now USB3) make life simplest. They have the advantage of offloading the most critical realtime processing from the Windows CPU which may be bothering with checking for updates or viruses or etc etc. |
#39
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Stereo INPUT on laptop?
Jason wrote:
On Mon, 29 Jun 2015 14:16:41 -0400 "Paul" wrote in article IMPLEMENTING UNIVERSAL JACKS ON HD AUDIO CODECS I'd never seen any of this - fascinating. I do a lot of audio work, but it's mostly processing of recordings made on other, dedicated digital recorders and have wrestled with Windows' weirdness regarding sound "cards" (be they PCI plug-ins or USB addons). I have come to conlude that external boxes attached via USB (now USB3) make life simplest. They have the advantage of offloading the most critical realtime processing from the Windows CPU which may be bothering with checking for updates or viruses or etc etc. The weird part, is how hard it is to get that information. I've seen it mentioned a couple times, but it never seems to have whizzy marketing terms associated with it. I assumed someone had patented it as a technique, and everyone else was "renting" the patent. The other surprise, is the method hasn't bitten anyone. No complaints about it. I guess if your dog or cat heard it, the tone burst only exists for 2 milliseconds. Paul |
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Stereo INPUT on laptop?
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#41
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Stereo INPUT on laptop?
In message , Brian
Gregory writes This looks cheaper. http://www.ebay.com/itm/USB-6-Channe...ptical-Sound-C ard-Adapter-For-PC-Laptop-Skype/141570512841 It looks as though it is good value, but who can tell from that shambolic specification. It looks as though internally it is working at 48kHz sampling rate and may, or may not, do sample rate conversion for other sampling rates via some external driver. It appears to record analog only at 48kHz and the aidio (as opposed to audio with video) standard sample rate is 44.1kHz. -- Bill |
#43
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Stereo INPUT on laptop?
Bill wrote:
In message , pjp writes In article , says... Jason wrote: On Mon, 29 Jun 2015 14:16:41 -0400 "Paul" wrote in article IMPLEMENTING UNIVERSAL JACKS ON HD AUDIO CODECS I'd never seen any of this - fascinating. I do a lot of audio work, but it's mostly processing of recordings made on other, dedicated digital recorders and have wrestled with Windows' weirdness regarding sound "cards" (be they PCI plug-ins or USB addons). I have come to conlude that external boxes attached via USB (now USB3) make life simplest. They have the advantage of offloading the most critical realtime processing from the Windows CPU which may be bothering with checking for updates or viruses or etc etc. The weird part, is how hard it is to get that information. I've seen it mentioned a couple times, but it never seems to have whizzy marketing terms associated with it. I assumed someone had patented it as a technique, and everyone else was "renting" the patent. The other surprise, is the method hasn't bitten anyone. No complaints about it. I guess if your dog or cat heard it, the tone burst only exists for 2 milliseconds. Paul All of this has made me want to plug a stereo output into my headphone jack on my laptop (Compaq CQ60) and see what happens given it doesn't have a dedicated line-in connection I, too found this interesting and fascinating. I've already tried on a Realtek machine and it didn't appear to change anything. I might dig out some components later and see if I can trigger anything. The way I have always believed the jack detection worked was a described in this excerpt from 7.4.2 in the pdf Paul referred to: Each jack must have an isolated switch (normally open), as shown in Figure 97, which closes when a plug is inserted into that jack. A “power of two” parallel resistor network is connected to a single jack detect or “Sense” pin as shown. The codec is required to use the measurable impedance of this network to determine which jacks have plugs inserted and set (or clear) the corresponding “Presence Detect” bit(s) in the “Pin Sense” control (see Section 7.3.3.15) for that Pin Widget or jack. The codec circuitry must appropriately remove switch bounce of up to 250-ms duration. But that's part of the fun. That's what the spec says, and the majority of computer cases, the front jacks don't have the side contacts needed. So when you get a response from those, that leaves impedance sensing. Also, on RealTek, there might be a tick box for sensing. "Enable Auto Popup Dialog" OK, I did some testing here, on the new motherboard. It has the requisite BIOS "AC'97 header or HDAudio header" setting. Which really shouldn't be in the BIOS. The RealTek control panel also has a tick box for the front panel type, so when testing, I have to be careful to match the BIOS setting and the control panel setting. When I test the rear jacks, I get confirmation something is plugged in. But not what type of device is plugged in. No retasking is evident there. The RealTek responds according to the traditional role of the connector. The lime green connector on the back, when you plug in something, takes you to the speaker configuration panel. Big deal. So I started experimenting with front panel assemblies. My well stocked junk pile, has an AC'97 assembly (with properly removed loopback wires). I have a second AC'97 which has the wrong wiring, and I didn't plug that one in. I used the one that has only five wires coming off the back of the 2x5 connector. When flipped to AC'97 mode, using AC'97 modern style wiring, *nothing happens*. The RealTek is incapable of detecting anything in the front. And a side effect of this, is I can't listen to music with my 32 ohm headphones (measured and verified). The Realtek doesn't have a manual selector for front or back audio, so I'm stuck on LineOut on the back. If I plug in the HDAudio wiring assembly and connectors, set both the BIOS to HDAudio wiring, and the RealTek panel tick box to HDAudio wiring, it works. The side contact is being used in this case, to detect that something is inserted. Still no evidence that RealTek is using impedance sensing. When I plug my headphones in the front (green) headphone jack, the headphones take over the stereo output, and the rear speakers are muted. If I plug the headphones into the microphone jack, I'm flipped to the microphone control panel, and there is no evidence that the RealTek has figured out it is not a microphone. Summary: My fancy RealTek ALC892 only seems to do side-contact sensing. And it only switches rear speakers to front headphones, if your computer case has HDaudio siring (doesn't work for AC'97 wiring). It won't retask, by noticing headphones are plugged into the front microphone jack (even though the motherboard manual implies it does). I found a datasheet for the RealTek (a datasheet covered by NDA on the RealTek site, but available elsewhere). "The ALC892 does not support hardware impedance detection. This field is read as 0s." ******* I tried using the RealTek as an oscilloscope. I connected RealTek microphone in, to SoundMax connectors on the other computer. And I was not able to see the Soundmax making a reading. The RealTek has 192KHz sampling capability. The spec sheet says it is flat to 76.8KHz. Yet attempts to capture a 24KHz test signal, were giving reduced amplitude. And the RealTek just didn't seem to be seeing the transient event. The Soundmax AD1988 is a 192KHz max sampling HDaudio chip. (I mistakenly set the sample rate at 96KHz, not that it matters.) And I did manage to capture the measurement event. First, I plugged my male-to-male audio cable into the Microphone-In on the back. (That would cause a measurement event, but that seemed to be gated off and I couldn't see it.) Next, I plugged the other end of the cable into the Center-Sub hole, pretending to be connecting a speaker. And the weird part was, I got a *11.7KHz* test tone (8 cycles at 96KHz per cycle of the test tone). Which is audible on the recording of the event. This is not a normal series of events for me, which is why I've never heard it before. But at that frequency, the test is plainly audible. I could hear the "pip" in my speakers, when the recorded signal was played back. http://i58.tinypic.com/344rq14.gif The AD1988 has one sentence claiming it "does something with impedance", but the actual details must be in some other document. They're not in the spec itself. So now I don't know if the 11.7KHz was intentional or not. Paul |
#44
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Stereo INPUT on laptop?
In message , Paul writes
Bill wrote: In message , pjp writes In article , says... Jason wrote: On Mon, 29 Jun 2015 14:16:41 -0400 "Paul" wrote in article IMPLEMENTING UNIVERSAL JACKS ON HD AUDIO CODECS I'd never seen any of this - fascinating. I do a lot of audio work, but it's mostly processing of recordings made on other, dedicated digital recorders and have wrestled with Windows' weirdness regarding sound "cards" (be they PCI plug-ins or USB addons). I have come to conlude that external boxes attached via USB (now USB3) make life simplest. have the advantage of offloading the most critical realtime processing from the Windows CPU which may be bothering with checking for updates or viruses or etc etc. The weird part, is how hard it is to get that information. I've seen it mentioned a couple times, but it never seems to have whizzy marketing terms associated with it. I assumed someone had patented it as a technique, and everyone else was "renting" the patent. The other surprise, is the method hasn't bitten anyone. No complaints about it. I guess if your dog or cat heard it, the tone burst only exists for 2 milliseconds. Paul All of this has made me want to plug a stereo output into my headphone jack on my laptop (Compaq CQ60) and see what happens given it doesn't have a dedicated line-in connection I, too found this interesting and fascinating. I've already tried on a Realtek machine and it didn't appear to change anything. I might dig out some components later and see if I can trigger anything. The way I have always believed the jack detection worked was a described in this excerpt from 7.4.2 in the pdf Paul referred to: Each jack must have an isolated switch (normally open), as shown in Figure 97, which closes when a plug is inserted into that jack. A “power of two” parallel resistor network is connected to a single jack detect or “Sense” pin as shown. The codec is required to use the measurable impedance of this network to determine which jacks have plugs inserted and set (or clear) the corresponding “Presence Detect” bit(s) in the “Pin Sense” control (see Section 7.3.3.15) for that Pin Widget or jack. The codec circuitry must appropriately remove switch bounce of up to 250-ms duration. But that's part of the fun. That's what the spec says, and the majority of computer cases, the front jacks don't have the side contacts needed. So when you get a response from those, that leaves impedance sensing. Also, on RealTek, there might be a tick box for sensing. "Enable Auto Popup Dialog" OK, I did some testing here, on the new motherboard. It has the requisite BIOS "AC'97 header or HDAudio header" setting. Which really shouldn't be in the BIOS. The RealTek control panel also has a tick box for the front panel type, so when testing, I have to be careful to match the BIOS setting and the control panel setting. When I test the rear jacks, I get confirmation something is plugged in. But not what type of device is plugged in. No retasking is evident there. The RealTek responds according to the traditional role of the connector. The lime green connector on the back, when you plug in something, takes you to the speaker configuration panel. Big deal. So I started experimenting with front panel assemblies. My well stocked junk pile, has an AC'97 assembly (with properly removed loopback wires). I have a second AC'97 which has the wrong wiring, and I didn't plug that one in. I used the one that has only five wires coming off the back of the 2x5 connector. When flipped to AC'97 mode, using AC'97 modern style wiring, *nothing happens*. The RealTek is incapable of detecting anything in the front. And a side effect of this, is I can't listen to music with my 32 ohm headphones (measured and verified). The Realtek doesn't have a manual selector for front or back audio, so I'm stuck on LineOut on the back. If I plug in the HDAudio wiring assembly and connectors, set both the BIOS to HDAudio wiring, and the RealTek panel tick box to HDAudio wiring, it works. The side contact is being used in this case, to detect that something is inserted. Still no evidence that RealTek is using impedance sensing. When I plug my headphones in the front (green) headphone jack, the headphones take over the stereo output, and the rear speakers are muted. If I plug the headphones into the microphone jack, I'm flipped to the microphone control panel, and there is no evidence that the RealTek has figured out it is not a microphone. Summary: My fancy RealTek ALC892 only seems to do side-contact sensing. And it only switches rear speakers to front headphones, if your computer case has HDaudio siring (doesn't work for AC'97 wiring). It won't retask, by noticing headphones are plugged into the front microphone jack (even though the motherboard manual implies it does). I found a datasheet for the RealTek (a datasheet covered by NDA on the RealTek site, but available elsewhere). "The ALC892 does not support hardware impedance detection. This field is read as 0s." ******* I tried using the RealTek as an oscilloscope. I connected RealTek microphone in, to SoundMax connectors on the other computer. And I was not able to see the Soundmax making a reading. The RealTek has 192KHz sampling capability. The spec sheet says it is flat to 76.8KHz. Yet attempts to capture a 24KHz test signal, were giving reduced amplitude. And the RealTek just didn't seem to be seeing the transient event. The Soundmax AD1988 is a 192KHz max sampling HDaudio chip. (I mistakenly set the sample rate at 96KHz, not that it matters.) And I did manage to capture the measurement event. First, I plugged my male-to-male audio cable into the Microphone-In on the back. (That would cause a measurement event, but that seemed to be gated off and I couldn't see it.) Next, I plugged the other end of the cable into the Center-Sub hole, pretending to be connecting a speaker. And the weird part was, I got a *11.7KHz* test tone (8 cycles at 96KHz per cycle of the test tone). Which is audible on the recording of the event. This is not a normal series of events for me, which is why I've never heard it before. But at that frequency, the test is plainly audible. I could hear the "pip" in my speakers, when the recorded signal was played back. http://i58.tinypic.com/344rq14.gif The AD1988 has one sentence claiming it "does something with impedance", but the actual details must be in some other document. They're not in the spec itself. So now I don't know if the 11.7KHz was intentional or not. Paul I haven't had time to do anything else on this, and I really subscribe to Jason's view that the best advice is to use a usb interface device. I have some oldish Reatek schematics somewhere, which is where I will have seen the jack sensing resistor ladders, I expect. It would be good it someone had the time and selection of motherboards and laptops to research this, but life is short. I did some work years ago on laptops that caused interruptions in the data stream when the internal speakers were above a certain volume. By the time I had a useful database of problem machines, most were obsolete. It was almost certainly the regulation of some internal power supply, but I never proved anything useful, except that a large number of laptops had a big problem. -- Bill |
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