> Maybe I wasn't clear what I was asking. I was asking for a > carrier to be injected that produced an audio tone of less > than 900Hz so that the third harmonic of that was within the > passband. I'm interested in the DSP and if that is > introducing the effect I'm hearing
As has been stated a dozen times in a dozen different ways, what you are hearing is simply the effect of overdriving the audio amplifiers. I posted the following table showing harmonic distortion products for the speaker amplifier the other day: > The following table shows harmonic levels relative to a 500 Hz > reference tone at the given voltage across an 8 Ohm speaker. > 0 dB is 1V Peak (.7V RMS). +10 dB represents 2.25V RMS (signal > + distortion). +13 dB is 3.2V RMS (the speaker amplifier is in > the compression region at the threshold of clipping) and +15 > dB is 4V RMS (the speaker amplifier is in hard clipping). > > Reference 2nd 3rd 4th 5th 6th 7th 8th 9th > ============================================================ > +15 dB -37 -15 -45 -26 -60 -43 -51 -37 > +13 dB -49 -31 -51 -35 -57 -39 -63 -49 > +10 dB -70 -68 -95 -67 -85 -69 -85 -73 > 0 dB -66 -74 -70 -77 -73 -76 -77 -80 > -10 dB -54 -66 -63 -90 -73 -82 -80 -87 > -20 dB -50 -78 -68 -74 -73 -74 -74 -78 > > In order to drive the audio amplifier hard enough to create > the distortion, it was necessary to disable the AGC or set > AGC SLP to low values (reduce the AGC reduction for strong > signals). Until the level is increased to the point that the amplifier is in compression and/or clipping, harmonic levels are extremely low. Here is a similar set of data points for the headphone output: 8 Ohm (old Yaesu) headset Reference 2nd 3rd 4th 5th 6th 7th 8th 9th ============================================================ -6 dB -60 -36 -74 -37 -73 -39 -75 -44 -7 dB -60 -69 -79 -75 -85 -77 -87 -81 -10 dB -61 -69 -82 -60 -73 -66 -87 -80 -20 dB -72 -60 -73 -66 -74 -70 -75 -74 -30 dB -61 -56 -63 -64 -65 -67 -66 nf 32 Ohm (computer) headset Reference 2nd 3rd 4th 5th 6th 7th 8th 9th ============================================================ +1 dB -62 -20 -68 -28 -82 -50 -70 -46 0 dB -62 -73 -89 -79 -90 -84 -94 -86 -10 dB -70 -66 -80 -73 -85 -80 -86 -81 -20 dB -72 -60 -73 -66 -74 -70 -75 -74 -30 dB -52 -52 -52 nf -54 -60 -55 nf 200 Ohm (Heil Proset) headset Reference 2nd 3rd 4th 5th 6th 7th 8th 9th ============================================================ +4 dB -64 -48 -90 -47 -84 -50 -80 -53 +3 dB -65 -79 -95 -86 -98 -93 -97 -93 0 dB -68 -79 -82 -84 -86 -80 -84 -83 -10 dB -76 -75 -82 -86 -84 nf -86 nf -20 dB -72 -80 -73 nf -75 nf -76 nf 0 dB is 770 mV RMS (1V Peak) measured for the reference tone across the headphone element - total audio level will be somewhat higher with distortion/noise. Note: in every case harmonic levels are extremely low, generally down more than 60 dB right to the point that the headphone amplifier goes into compression/clipping. "nf" indicares harmonic product not measurable (in the noise floor). The table shows the harmonic levels at maximum "linear" output and again with the reference tone raised just 1 dB above the clipping point. Now my ears are not "young" and have some loss from more than 30 years around control room monitors that were always "too loud" and the many hours around the big pumps/blowers in the TV transmitter sites. Still, with all of the tested headphones the audio level is nearly painful at least 3 dB before the amplifier went into clipping and the harmonic products exceed -60 dB. Based on these and previous tests, anyone who can not get adequate headphone levels without distortion should be look- ing for more efficient headphones and/or loudspeakers. 73, ... Joe, W4TV > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Paul Fletcher > Sent: Thursday, September 04, 2008 12:37 AM > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] Added LIN OUT measurements > > > > Jim, > > Maybe I wasn't clear what I was asking. I was asking for a > carrier to be injected that produced an audio tone of less > than 900Hz so that the third harmonic of that was within the > passband. I'm interested in the DSP and if that is > introducing the effect I'm hearing. As for the difference > between impedance and resistance your point is duly noted and > the only way this could be achieved is to use a set of Heil > cans as the load (or something with very similar characteristics). > > 73 Paul. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
