That is the question…
Would it work to my advantage to apply compression to sound tracks like music, talk and podcasts before adding them to the library for later use on the radio?
That is the question…
Would it work to my advantage to apply compression to sound tracks like music, talk and podcasts before adding them to the library for later use on the radio?
Remember i am broadcasting on both am and fm without much processing, i use very little processing on the low cpu version of stereo tool.
I want to normalize then add the compression to mp3’s.
Well the main drawback to
Well the main drawback to precompressing all your files is that you can’t very well “tweak” that after it’s done. You might find different software or a setting you like better or even a hardware compressor somewhere down the road, and then not be able to take full advantage of it.
Sure, if you keep backups of all the files you’d be ok and could go back to those older versions, but then the work you put in with compressing the tracks was kinda wasted.
Normalizing isn’t too bad *if* you like normalized tracks and aren’t running an agc or anything. But the compression at least I’d say is worth leaving off so you can add it in the audio chain. Besides, what will sound best on you fm and your am won’t likely be the same exact amount of compression.
Largely a matter of personal tastes, though.
Daniel
Agreed, it was truly awful..
I tried it and didnt like it.
It was to say the least terrible. I believe it added more hash that I dont want on either band.
I did try one more without the compression but with normalizing, it was okay but still lacked something.
We use Audacity here because it’s free and it works.
But yeah, i didnt do this without making certain i was not destroying the original material, i always back things up.
Thanks Daniel
Compression…it depends
The universal answer is “it depends”. I think Daniel’s answer is worth noting in that he suggests not compressing the original material as I read in his reply. Once you modify the original material there is no going back.
So, as you prodeed, ask what you are trying to do. Here, I compress using an Alesis Nanocompressor for FM only because I use my FM setup for wireless headphone audio during late night movie viewing so I can listen to the audio on my Walkman and not disturb the family. With the modern audio on movies I find that the dynamic range is just too much for my tired ears to follow given the loud and then soft content. So I set the compressor to keep the levels pretty much constant so my eardrums are not turned inside out with the surprise loud sounds in movies.
Now, for the music purists this may not be a good way to go, yet my most loyal listener (my wife) during the day when I transcast classical music via my humble station to her portable and “big home theater rig” thinks things are just fine with the compression disregarding that she doesn’t know compression from expression. It just sounds good to her and that keeps both of us happy. Many listeners are not discerning enough to know the difference with or without compression as am I unless I am listening on headphones, and even then the compression is not an issue with me.
On AM I use the internal compression built into my SSTRAN transmitter which maintains a high level of modulation but my programming is voice and talk rather than music so purity of the audio is not paramount.
My best advice is to process to suit yourself, but as previously mentioned, I would not modify the source material so you can always go back. For hobby broadcasting some would say compression allows you to maintain a high modulation which increases your range but I don’t think this is a valid statement. What it does do is prevent over modulation which creates distortion and which we try to avoid for part 15 applications but other than this I don’t see much value beyond that which I have mentioned.
Neil
Oops, I think I misunderstood…
As I checked this thread many hours after my reply above I realized that you are probably talking about file size compression instead of amplitude compression as I had assumed. Therefore if this is the case my answer above doesn’t make much sense in this context. But, nonetheless, I hope it was interesting to the readers though it is off topic.
Neil
Ok guys…
To make this a little easier on all of us, i may have posted that question in haste as i have been struggling with the audio on my station for quite some time now.
The reason i dont have much if any processing on either station (aside from the compression on the sstran) is for obvious reasons. Processors are pricey, way out of my reach right now.
So ive been trying different software based processors.
The big problem there is one computer feeds the audio to both transmitters. FM and AM are not the same when it comes to audio, they both have different means of moduating. And I know most of you understand the diffences so i wont get into that. Im fine with the sound of the FM, but AM on some material has a distortion on the bass, while highs and mids are fair. Turning down the modulation control on the sstran helped that but then i lose some modulation. The compressor had to be re-adjusted to make up for the change.
I was compressing the audio aswell as normalizing wich as i stated before, does not work. Whew. Sorry ’bout that. i must’ve had too much coffee lol.
Now I Understand
OK, now I think I am on board with this. What threw me was the idea of “precompression” of the files.
Your bass problem with the SSTRAN leads me to think that your bass is running at a relativly high level compared to the treble as it is fed to the SSTRAN. You may know that the SSTRAN has a jumper which accentuates the highs. Maybe you could try this to bring the bass and treble into balance and then adjust the modulation and compression.
The Nanocompressor I mentioned is only connected to my FM chain, not the AM and I seldom simulcast so I have almost no experience with this beyond what I mentioned. You know your budget better than I but I picked up my Nanocompressor on ebay for about $40 and have been very happy with it. True, it is not a professional broadcast unit but it works very well for my purposes and my FM signal sounds great. Plus, it has a LED VU indicator on the front panel which permits me to keep an eye on the signal level. Even so, it is pretty much plug and play and I rarely have to twiddle the knobs.
The only downer is that this unit uses 1/4 inch phone connectors (the most reliable connectors for audio I have ever found) which can cost as much as the compressor for a full set. OTOH, if you are good with soldering, you could use some cheap RCA patch cables cut in half, run through the jacks’ cannulae and soldered to the PC board to save $$. Just a thought.
Neil
Just a thought
I don’t know what gear you might have lying around.. But if you happen to have an old stereo with line out jacks (preferably) or a headphone out, AND that happens to have an EQ on it, you could tune it to your FM transmission and then feed the AM transmitter with the output from the stereo. Then you could use the receiver’s EQ (or maybe even just the bass/treble controls, if it has those instead) to touch up the audio for sounding better on the AM transmitter. Between that and the controls on the SStran, you can probably get it pretty good.
I used to run my AM SStran off a stereo’s line out. I use a modified portable radio to feed the AM transmitter for some of my experiments. “Cheapo” portable receivers can often sound pretty good if you bypass the pitiful excuse for audio amplifiers and speakers they usually come with.
Daniel
Another Thought Regarding Bass Distortion
As I thought more about your posts I came to another thought which you might consider.
My SSTRAN, great unit that it is, is pretty touchy about proper antenna tuning. I experienced a bout of bad audio and when I checked the envelope on my scope the distortion was evident. Retuning my unit according to the instructions cleaned thing up beautifully.
So, I am suggesting that you check the tuning on your SSTRAN. This could be the problem rather than the audio feed….One thing a time.
Neil
Bass distortion vs. Overdriven Receiver
I will check that as well Neil, youve made a good point there and i admit i have overlooked that.
But i have been wondering too if i am also experiencing some overdrive on the am receiver.
In the house i use a Dura-brand am/fm cd/cass. boombox.
That radio has one heck of a receiver on am, especially at night. Stations are booming in here every evening wich leads to another possibility.
Front end overload.
Has anyone ever had this problem? I know the cure for it, a receiver with rf gain. I may just have to call a friend and borrow a good multi-band, lightning took my rat shack DX 390 out. (wich is amazing, it wasnt even plugged in or even had a antenna connected)
But at any rate i will be checking my tuning/matching tomorrow. I hear no distortion on the source, wich is the soundcard in my on-air computer, so we can rule that out.
I’ll let you know what i come up with.
p.s. the idea of feeding audio from a receiver is a good idea too. Thanks
Bass distortion vs. Overdriven Receiver
I think I may be able to offer some help here. rock95seven, I think you have a very good ear for distortion. It is one thing to observe the modulation envelope on a scope, but it is another world when judging by ear. Over a long time, I have trained myself to hear the distortion while watching the scope. What I found is exactly as you describe. The most noticeable result of over modulation on the SSTRAN is bass distortion, exactly as you describe.
The modulation depth is controlled by the MODULATION control on the AMT3000. I have found that setting the control to the 11 o’clock position consistently results in near 100% modulation. The GAIN and COMPRESSION controls have little effect on the modulation percentage. I recommend the following settings for the 3 controls:
GAIN: 3 o’clock
MODULATION; 11 o’clock
COMPRESSION: 9 o’clock
(assuming you mounted the knobs so the knob pointers align with the slots on the end of the pot shafts)
The GAIN setting depends on the level of the audio source and may need to be adjusted. The COMPRESSION setting depends on the dynamic range of your audio source material and the amount of compression already present in the source material. Usually, little or no compression is required, but if you play classical music sources (CD or good internet), you will need to crank up the COMPRESSION control to level the extreme low and high volume levels. Compression is simply an automatic volume control.
Regarding receiver overload, yes, it can very definitely be a problem. I have experienced this several times. One way to test for this is to rotate the receiving radio to orient the loop stick antenna in different directions. You should find a direction that reduces the received signal. If the distortion reduces, you can conclude that overload is the problem. You can eliminate this problem by shortening the transmitter antenna or very slightly detuning the transmitter by rotating the trimmer capacitor slightly off peak.
PhilB
SSTRAN Distortion
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PhilB wrote”It is one thing to observe the modulation envelope on a scope, but it is another world when judging by ear. Over a long time, I have trained myself to hear the distortion while watching the scope.”
It is good to know that someone other than myself can correlate perceived audio distortion from an AM transmitter with what is observed on the oscilloscope. But, Phil, I ask that you please comment on my remark that less than proper tuning of the SSTRAN can result in distortion. I have observed on the scope and heard on the monitor receiver audio distortion but this distortion goes beyond just audio in that the carrier waveform I observed showed marked distortion of the carrier when the transmitter was not tuned properly.
The SSTRAN produces excellent audio on a receiver and textbook waveforms on the scope when presented with a proper load, but when mistuned this is not the case. Your suggestion to “off tune” to reduce receiver overload seems to me, based on my experience, to invite both audio and RF distortion.
Your comments on this will be most welcomed.
Neil
You were both right…
I removed the coil and whip , used the antenna that came with the sstran, retuned and set the controls as PhilB suggested and the audio cleared up beautifully.
Then attached the coil/whip again and repeated the steps Neil and PhilB suggested, the distortion was gone this time but coverage was a little less this time.
That’s fine with me, this is only for experimental purposes until i find the sweet spot with the coiled antenna. Then when i have it the way i want it the antenna and sstran will go outside.
“Neil Wrote”
It is good to know that someone other than myself can correlate perceived audio distortion from an AM transmitter with what is observed on the oscilloscope. But, Phil, I ask that you please comment on my remark that less than proper tuning of the SSTRAN can result in distortion.”
Indeed it can, some of you that are hams or even old CB’ers like myself will know that on AM your signal suffers when the modulation shows backwards swing on a reliable s-meter. While the characteristics are different with transceivers vs. transmitters, modulation can effect your carrier , if there is reflection from the antenna back to the transmitter then there may very well be some distortion cause by addition rf being imposed on the transmitter causing the carrier to become unstable.
I have the general idea in my head but conveying it to everyone here is had for me. I hope you have the gist of what im getting at. This can be reproduced with a scope and a transmitter. Just intentionally cause a bad match and see what happens on the scope.
AM transmitter checking and monitoring
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Very happy here to learn that what PhilB and I posted helped you with your problem and thanks for reporting back.
Yep, I know about “downward modulation” which usually shows up as a change in the plate current of a transmitter with the audio….not good. The S meter on a receiver is less reliable and can change even if the signal is perfect.
Maybe a lot of folks don’t have the interest or equipment which I do, but in any case I thought I would mention a great way to monitor AM and SSB transmitters. It is known as the trapezoidal pattern.
Essentially what you do is feed the modulated carrier on one channel of a scope (usually the Y axis) and the audio into the final stage on the other channel (x axis) with the scope set up for X-Y display. On AM you will see a trapezoidal (essentialy a triangle) pattern. The top and bottom edges of the display should be perfectly straight lines. Also, if you over modulate a tail appears at the end of the triangle.
On SSB, you see a bowtie pattern.
It becomes a very easy method to monitor/check for proper operation with experience which I used oh so many years ago to keep my KnightKit AM unit going. I also used this when I designed, built, and operated AM transmitters at a college carrier current station.
I recently did this with my SSTRAN and with the proper load and tuning the pattern was “textbook perfect”.
For those with a scope and the interest, google it.
Neil
SSTRAN Distortion
Neil,
You are absolutely correct that a bad match to the antenna can cause the AMT3000 to distort. When I suggested de-tuning the trimmer slightly to reduce the signal level, I was assuming there was already a decent match. This will work fine without distortion.
Distortion due to a bad antenna match occurs when the RF voltage waveform at the collector of the output transistor exceeds the maximum 30V p-p level (twice the power supply voltage of 15 VDC). This causes clipping at +30V and 0V. This condition will occur when using the base-loaded external antenna and the 0% modulation measured voltage at the meter terminals is above 13VDC. It is not possible to get clipping using the wire antenna unless resistor R18 is removed and the frequency is set below about 1000 kHz. Removing R18 is a suggested configuration in the manual for getting slightly more signal out when using the wire antenna and operating above 1000 kHz.
I really don’t advocate detuning the AMT3000, but if receiver overload is really a problem when using the wire antenna, it is a possibility. A better suggestion would be to shorten the wire antenna and tune it to peak.
Phil B