9024 DSP 6 Band Compressor

[Zozo]

Has anyone here ever used the Behringer 9024 with AM Broadcast? I'm currently testing its performance using a little Mosquito for the time being, which seems to be doing the job rather well for bench testing.

I'm also using the Behringer Ultra Curve 8000 for some basic Parametric EQ'ing and Limiting before feeding into the 9024 to do the 6 Band Compression.

The 9024 came with no saved preset for broadcasting, so I've had to configure my own. Not sure if that's factory normal, as the unit is third hand to me.

9028-8020.jpg

[Albert H]

It was actually a pretty competent unit (for Behringer), but as I recall it produced some weird digital crud on the output, making it largely useless for FM stereo. However, there were some published modifications that overcame the worst of the problems....

I've never tried one on AM, but it should be capable of pretty good results. I'll see if I can find any settings for you.

My homebrew AM processor is a 3-band affair, and includes a slow AGC at the front end to even out long-term level changes, the three-band limiter, a clipper, a very accurate 6k5Hz lowpass filter and an overshoot compensator that really makes the thing sound "louder" than all the rest! One trick I found - quite early on - was to introduce some "treble lift" from about 1k5Hz upwards. If not overdone, it "brightens" the sound and really improves intelligibility on a noisy channel at night.....

[Zozo]

All-in-all I’m very happy so far, but there maybe one concern regarding the firmware of the 9024. After some internet searching of this DSP, I came across some mentions of this being a must have upgrade due to bug issues and enhancements. Mine is currently running version 1.2b.

I have no idea what problems these bugs in the firmware introduce, or what enhancements the latest version has? But I do see that Behringer still offers the latest/final firmware 1.3a for download on their website. A 256K EEPROM and programmer is required, so that's probably the next thing I should get done. However I've not noticed anything that would suggest it’s not working correctly with the current firmware?

If you are able to share some 9024 settings you've configured that would great thanks. Also all noted on the treble lift, the Ultra Curve is set to a gradual increase from 1K to 8k with a sharp cutoff starting from 10k to 20k. It perhaps a little bit too treble high the way I have it EQ'd at the moment, but It does as you say cut through the noise on the band, and especially at night.

Finally your 3 band processor sounds interesting. Is this in the public domain, i.e been shared on here? I'm looking for something compact and low voltage to use when portable operating.

[Albert H]

I can put a version of the 3-band up here. It's based on a project I worked on about 40 years ago for an American broadcast gear company! In the full scale product. I used PWM attenuators for the level control (with a clock frequency of around 140 kHz to make filtering out the switching artifacts really easy). The reason for using PWM was that it makes channel to channel balance easy (so that a stereo image is always perfect), and because the distortion from this method is vanishingly small - certainly a couple of orders of magnitude better than the Voltage Controller Amplifier ICs available at the time (or available at a reasonable price these days!).

The trickiest part of the design is getting the separation filters correct, and maintain phase and relative level accuracy without the need for bench tweaking after construction (very expensive and labour-intensive!), whilst using reasonable component tolerances.

The simplified (and slightly modernised) AM version I built used MC3340 attenuator ICs, since they were cheap and readily available and had good enough fidelity. These days they're still available if you search a bit. I bought a strip of them (50 devices) for about £17 last year.

The only thing to be careful about is making certain that any RF that's about doesn't mess with the level control inputs on the 3340's, otherwise you can get a muted output!

I'll rummage around and see if I can find the circuit sketches. I'll try to put them up here shortly.

[reverend]

@Albert, I'd be very interested to see your 3 band circuit as it sounds nearly identical to the one I put together. Great minds think alike or fools beg to differ, eh?

@Zozo, I used one of those Behringer 6-band devices but on FM, and followed by a limiter as there isn't one on the output, its just a processor. Got some very nice sounds out of it but it took a lot of fiddling around to do that. I sold it years ago, so don't have the settings otherwise I'd share them but persevere with it as it's worth the effort, especially at the price. One fault it has is that if you set some of the controls towards extreme values, it locks up and you have to do a full reset.

[jvok]

One fault it has is that if you set some of the controls towards extreme values, it locks up and you have to do a full reset.

Maybe thats what the firmware updates for?

[mpx]

I believe one of the main reasons for the 1.3 update was to fix the peak limiter, allowing for a shorter release time. They might have also tweaked the ultramizer section but don't quote me on that. I've had both versions and the 1.3 sounded a bit cleaner, but for AM you won't notice the difference.

[Zozo]

@Rev, All noted on the locking up issue, I've not experienced that as of yet, But thanks for the heads-up. Shame you don't have the parameters still. But I will share mine, once I've stopped tweaking

@MPX, Thanks for the advice. I've not bothered with the firmware update as yet, mostly because I don't have a spare 256K EEPROM to hand.

[Zozo]

Small video demonstrating the DSP's (Mine your ears @ 00:43)

Time Stamp
00:00 All DSP's ON ( Fully compressed and limited for EU 9K )
00:30 Ultra Curve OFF ( High frequency modulation peaks )
00:43 Ultra Dyne OFF ( Mind Your Ears! )
01:02 Ultra Curve ON ( Just visible out of bandwidth peaks )
01:15 Ultra Dyne ON ( Fully compressed and limited for EU 9K )

Note there is a small hum / buzzing on this recording which is not present on the air. This seems to be an issue with my laptop and capture software, or RF getting into things it shouldn't.

Processing Line-up:
Ultra Dyne 9024 feeding a Ultra Curve 8000

Audio Source, UK BASS RADIO live stream.

[mpx]

You could set the 6th band on the 9024 to cover 9k upwards and the set the output level to minimum. That acts as a crude low pass filter.

[sinus trouble]

Blimey! That sounds pretty decent for AM!!!

I have that tune on vinyl here and i doubt the everyday listener could tell the difference!

[Zozo]

@MPX That's a good idea, and I will give that a try. As you know it's easy to make and save another configuration profile to see how it sounds.

@SINUS. Yes I think it sounds very good considering the Mode and Bandwidth. The main problem I experience is not QRM / Noise on the band. It's the quality of the modernish receivers that have Medium Wave. Most are a disappointment in the audio quality department, compared to those produced back in the 70's and 80's.

I have a Pioneer VSX-D510 Receiver / AMP combo that I purchased back in 1999 I think, possibly 2000? Anyhow it's really poor sounding on Medium Wave. I have old radios both Valve and Solid State that put this thing to shame.

[jvok]

Always surprising how good AM can sound with a strong signal. Especially on an sdr where you can set it for wider bandwidth

[Zozo]

I couldn't agree more Jvok, I have several SDR's here. Not to keen on the RTL's, but my RSP1A and Airspy+HF I both use often.

[LeeCavanagh]

I had o e of those once, just to try, but it made me then buy a 2nd hand TC Electronic DBMAX, seeif you an find one of those designed for broadcast 19inch racks, you wpuld be looking at paying between 370 and 570 for fair priced 2nd unit,

[Albert H]

Lee - I'd love to find a DBMAX for just £570! The cheapest secondhand (poor condition) one I've found is £1200!! Where did you buy yours from?

[LeeCavanagh]

Well, you should have got it from me when i sold it, i actually bought it for £350, then paid the uk partner to upgrade the board to the newer version so it was the same as the latest - that was well worth the small price tor uprade to latest firmware and newer dacs (they even gave me a new case , because they accidentally damaged the original, kind of them.
i’m not sure if i have the ebay confirmation but i can look.
I know its good for classical, and production (which i used it for), onair was ok but i didnt have anything to compare to at the time, ultimately i got rid as needed cash and wasnt using it any longer after giving up radio work.

[Albert H]

Drat! I always wanted to try one of those - I heard great things about them.

[LeeCavanagh]

Drat! I always wanted to try one of those - I heard great things about them.

Here is 1 that sold for £300 last year, this would need the upgrade
https://www.ebay.co.uk/itm/403992077323 ... edia=COPY

Mine looked pristine as new , still got the manual as I forgot to send and then sent them the link to the download instead.

You make me wish I’d kept it, personally wasn’t keen on the lcd parameters screen, but it had what you needed.

[reverend]

Fully compressed and limited for EU 9K

Although the AM channel spacing is 9 kHz, in theory this limits audio response to 4.5 kHz as the bandwidth occupied by an AM transmission is twice the highest modulating frequency. Anything more than this and you will be bleeding into the adjacent channel. The UK and some other countries relax this a little and in the UK, audio bandwidths of up to 6.5 kHz are licensed (with the need to fit a sharp filter to reduce any audio at 9 kHz).

As a pirate there's nothing stopping you using 9 kHz or even more of audio bandwidth but most receivers won't hear the difference as they're either RF or AF bandwidth limited. Modern SDRs, of course, will reproduce the higher bandwidth, so it depends who your audience is!