Sin & Cos curves over the first quadrant give panning with constant power summation. This is apparent from the trig identity: sin^2 + cos^2 = 1<br><br>(Whether or not constant power summation is the correct panning law for a particular listening environment is a subject of debate and personal taste. Things like mono compatibility can influence the decision.)<br><br>As for an analogue circuit to generate the panning law, that is what the first part of that schematic does. The switchable resistors allow the attenuation at the "panned center" position to be adjusted to achieve various different panning laws. I wouldn't consider it a hack though. It's an engineered circuit that performs the required function cheaply with acceptable accuracy.<br><br>FWIW, I would generate the curves digitally too. Either using a look up table on a PIC or polynomial approximation on a DSP. It really doesn't need to be that accurate as panning is quite a subjective quantity like volume. If someone pans something three-quarters to the left, and it doesn't sound far enough over they'll turn the pot a bit further round. And if it now sounds a bit too quiet they'll nudge up the volume a bit too until it sounds how they think it should.<br><br>-Richie,<br><br>---- drheqx wrote ----<br><br><div dir="auto">Thank you Tom. The DAC idea is really cool. It's true, performance will dictate performance. I can get away with less noise performance here but the linearity is important. Some of these pan circuits have a bump in the middle or a dip. I'll have to work that part out. This is something where a musician would certainly notice that bump. <div dir="auto"><br></div><div dir="auto">Mike</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Nov 27, 2020, 3:11 PM Tom Wiltshire <<a href="mailto:tom@electricdruid.net">tom@electricdruid.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word;line-break:after-white-space">Do you mean this one? “VCAs in a Pan potentiometer Application”:<div><br></div><div><span style="white-space:pre-wrap"> </span><a href="http://www.thatcorp.com/datashts/dn120.pdf" target="_blank" rel="noreferrer">http://www.thatcorp.com/datashts/dn120.pdf</a></div><div><br></div><div>Personally, I never liked the hacky make-it-nonlinear approach. In practice it works more than well enough. If it was me, I’d use a lookup table and a DAC. Whatever floats your boat, I guess…;)</div><div><br></div><div>Separate question: Is there any analog way that *does* give a constant power panning curve? I remember seeing the “expo crossfade” example from the SSM2024 datasheet which uses a differential pair to split a linear control current between two linear VCAs (e.g. not applicable to the expo VCAs we’re discussing here) . If I remember correctly, when I tried it, it gives subtle “hole in the middle” effect as a panner, as the volume apparently drops as the signal reaches the centre. This experiment was a long while ago though, and I might be mis-remembering.</div><div><br></div><div>What others have said about the VCAs is all true - you pick the cost/quality ratio you’re after and then the parts choice will make itself!</div><div><br></div><div>Tom</div><div><br><div>
<div>==================<br> Electric Druid<br>Synth & Stompbox DIY<br>==================</div><div><br></div><br>
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<div><br><blockquote type="cite"><div>On 27 Nov 2020, at 16:27, Ben Gebhardt via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" target="_blank" rel="noreferrer">synth-diy@synth-diy.org</a>> wrote:</div><br><div><div dir="auto"><div dir="ltr">I second what Eric said and would note that THAT has a good app note for a pan pot application which I used for a mastering grade cross fader. Worth a look.</div><div dir="ltr"><br><blockquote type="cite">On Nov 27, 2020, at 10:50 AM, Eric Schlappi <<a href="mailto:eric.schlappi@gmail.com" target="_blank" rel="noreferrer">eric.schlappi@gmail.com</a>> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><div dir="ltr"><div>if you are going off of the THAT Corp app note for equal power panning, it is totally possible to adapt that to the ssi2164. Just change the scaling and you need to invert and offset one side.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Nov 27, 2020 at 7:27 AM drheqx <<a href="mailto:drheqx@gmail.com" target="_blank" rel="noreferrer">drheqx@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto">I'm looking at the THAT2180A for a voltage controlled pan pot application. They're not cheap. Any ideas for a less expensive vc pan pot?<div dir="auto"><br></div><div dir="auto">Mike</div></div>
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