Analogue line level recording with inexpensive handheld MP3 players

Recording with software on a computer provides an alternative to hand held MP3/WMA recorders. In this article, the recording potential of inexpensive hand held records will be examined.

Hand held recorders may suffer from a number of problems. The most obvious limitations of hand held MP3/WMA recorders are likely to be:

* Poor battery life. Sure, this can be rectified by fitting a replacement, but doing so can be a potentially risky & difficult task – assuming one can even find a replacement battery!

* Limited storage capacity for long recordings. Fixed capacity recorders force users to only keep a very small selection of music or videos on the player, otherwise there is inadequate recording space available when needed.

Other potential headaches experienced with portable MP3/WMA recorders include:

* Automatic Level Control (ALC) is implemented for recording, which is not ideal for all programme material. ALC artificially restricts the dynamic range of the recording. Limiting dynamic range is considered undesirable for music, although it is applied widely to radio broadcasts. A pair of RCA Line Level Audio Attenuators may be required to ‘tame’ audio output levels from analogue components (e.g. Harrison Labs’ manufacture 3, 6 & 12 dB models, which retail from $34).

* Encoding quality. Line-in recording is frequently restricted to relatively low bit rates such as 128 kbps, 160 kbps or 192 MP3 compressed audio recording. These bit rates are not ideally suited for recording music. Gabriel Bouvigne recommends 256 kbps MP3 as a minimum encoding rate for music. Today, even sub-$100 cellular phones support lossless FLAC audio. Does compressed audio files (such as open source MP3, Apple’s AAC or Microsoft’s WMA) still offer relevance?

Creative & Samsung Hand held MP3 Players

Perhaps two of the most suitable MP3 players for recording include the Creative Muvo Vidz & Samsung YP-T8 MP3 players. Both are available in 1 GB capacities. This capacity means these devices are capable of performing recordings from analogue components lasting over 11 hours at 192 kbps MP3 (their highest recording bit rate). That would fill over seven 90 minute cassettes. Unfortunately, these players are extremely rare to find & cost over $80 in the second hand market.

1 GB capacity Creative Zen Neeon 2 models fit 16 hours of recordings at 128 kbps WMA (their highest recording bit rate). These are readily available, refurbished by the manufacturer priced from $45 (1 GB) up to $85 (4 GB).  It is difficult to overlook the fact that the 4 GB model will fit an impressive 66 hours of recordings (128 kbps WMA), but Creative’s Zen Neeon series cannot be recommended by the author. This is due to unreliability of the hardware, in particular the widespread reports of hard drive failures. The author’s Neeon 1 model will not start up.

Olympus Hand held Recorders

The Olympus WS-832 & WS-833 (from $160 new) record with PCM format as well as 256 kbps MP3 but probably audibly wreck bass response (e.g. timpani, kick drum & bass guitar) because of a sharp 40 Hz cut-off. The specified PCM recording frequency response is only 40 Hz – 21 kHz. Such a shame, because these voice recorders also feature fully adjustable recording level control.

Mini Disc Portable Recorders

Mini Disc portable recorders which use ATRAC implementations also suffer from similar restrictions on quality like MP3/WMA. The exception is if one owns the relatively rare Hi-MD recording models (examples, pictured below) & can also readily source affordable discs.

dietrich_liao_2006_mz-rh10

Sony MZ-RH10 © 2006 Dietrich Liao.

SONY DSC

Sony RH-1 © 2012 Jaen Yu.

Example: Recording with Zen V Plus & Samsung Yepp T7

Personally, the writer has enjoyed immensely recording on these tiny devices over the last decade. The primary advantages are due to their size. An honest evaluation of their performance is warranted.

In theory, portable digital recorders should perform better recordings than modern compact cassette boom boxes. Modern boom boxes incorporate poor quality recording heads with rapidly falling treble response over 10 kHz, not to mention poor wow & flutter performance (due to poor quality generic mechanisms) compared to the relatively high quality found in boom boxes during the 1980s & 1990s. During this period, some of these at the high-end boom boxes such as the 1990 model AIWA Strasser CSD-SR8 (photos here & here) featured Dolby C & Dolby B noise reduction as well as manual recording level control. If functional, these high-end boom boxes command very high prices today on auction sites.

Take, for example the Creative Zen V series recorders which are no longer manufactured, but still sold (currently priced from $80, manufacturer refurbished).

OLYMPUS DIGITAL CAMERA

Zen V © 2007 Brian Barnett.

When launched in 2006 for $230 USD the Creative Zen V Plus received favourable reviews. The playback audio quality was very good on the Zen V series with low levels of noise & distortion reported during measurements. The Zen V series uses the Media Transfer Protocol (MTP) to transfer video & audio files (including uncompressed PCM, as well as compressed MP3/WMA) in Microsoft Windows operating systems.

Creative’s Zen V players (as well as the Zen Neeon 2, mentioned earlier) would be more useful if the player did not encode line-in recordings in 160 kbps WMA format. Today, WMA offers less playback support than MP3 & AAC files so the future is not rosy.

Exacerbating this, is the fact WMA recordings are unsupported by loss less MP3 software editors such as MP3DirectCut if one needs to edit the recording. Converting recordings to PCM alleviates this but doing so offsets the primary advantage of compressed audio, the small file size!

josh_bancroft_2005_samsung_yepp

Samsung YEPP YP-T7 recorder in the bottom left © 2005 Josh Bancroft.

The other problems encountered when analyzing software measurements suggested that hiss & clipping may be problematic when recording on the Creative Zen V Plus & Samsung YEPP (Young Energetic Personal Passinate) model T7, pictured above. A Sangean PR-D8 (chosen because it supports 192 kbps MP3 line-in encoding) was used to double check any inconsistencies found with recordings made on the Zen & YEPP MP3 players.

Hiss

Surprisingly, recordings on the Zen exhibited 15 dB more high frequency noise (hiss) in a recording of silence compared to one made on a laptop sound card. These (admittedly imperfect) software measurements were of noise floor, made in Root Mean Square (RMS) amplitude. Another crude inspection using the meter (maximum range: -96 dB) suggested approximately 10 dB more noise in the Zen recording of silence.

Recording nothing ain't so silent on the Zen! © 2016 FM DXing.

Recording nothing ain’t so silent on the Zen! © 2016 FM DXing.

The Samsung YEPP recordings exhibited less than 3 dB more noise in recordings of ‘silence’ than the sound card which was expected – so very close to the performance of the sound card. Of three hand held recorders by different manufacturers, the YEPP outperformed all others in tests.

Recording nothing ain't so silent on the YEPP either! © 2016 FM DXing.

Recording nothing ain’t so silent on the YEPP either! © 2016 FM DXing.

Regardless, the A-weighted Signal to Noise Ratio (S/N) figures for analogue (line-in) recording from the sophisticated Wolfsen Microelectronics, Telechips, Texas Instruments & SigmaTel’s D-Major ‘codec’ Integrated Circuits (ICs) utilized inside these MP3 players do suggest 80-85 dB as minimum figures. But the noise is higher than the IC measurements because other hardware (such as LCD screens & poor component shielding) in the players may produce additional noise – perhaps even the encoding software. Hence, the actual real world S/N figures for recordings is typically lower than the ‘codec’ figures.

At this point it may be useful to compare more closely these low-cost digital recordings with their vintage analogue counterparts. The A-weighted Signal to Noise Ratio minimum figures for compact cassette tape recordings are as follows: tape recordings encoded with the commonly found Dolby B provide 68 dB S/N. The high-end, (but both less compatible & prevalent) Dolby C provides 78 dB S/N. The relatively rare high-end Dolby S provides 80 dB. There is likely to be negligible variation between ‘Dolbyized’ recording decks.

neil-_2009_jvc

JVC cassette deck © 2009 Neil.

frankpr_2014_gxc-760d

1978 vintage Akai GXC-760D cassette deck © 2014 FrankPR.

Modern low-end compact cassette recorders may not offer noise reduction provision, including many portable boom boxes & light weight mini systems. In fact, the new Prince re-issue cassette albums that were manufactured in the United States in latter half of 2016 are not recorded with Dolby B noise reduction for this reason; unlike vintage pre-recorded cassettes.

Yamaha PC-8 portable system with Dolby B & C noise reduction

Yamaha PC-8 portable system with Dolby B & C noise reduction.

sony-fh7-mkii

Sony FH-7 MkII portable system with Dolby B & C noise reduction.

Without noise reduction, the minimum Signal to Noise Ratio (A-weighted) is 58 dB, even worse on some machines with cheap mechanisms with figures as low as 52 dB S/N. In theory, these inexpensive modern tape recorders should create recordings with considerably higher hiss than is possible with digital recording using the aforementioned ‘codec’ ICs.

Clipping

Worse than noise added, a test recording from a compact disc component (original CD pressing of Roy Orbison’s Mystery Girl) showed clipping  in all software & also failed the ABX recording level tests, with the recordings on both the Zen & YEPP peaking in excess of -3 dBFS. This is despite the recording being made well below the peak (red coloured) levels on the recording level display. 3-6 dB RCA Line Level Audio Attenuators do tame output levels so the clipping does not occur, but are an unnecessary expense.

The process of encoding to compressed audio formats may cause clipping, so turning the input volume down may not necessarily address the problem in every instance. In those circumstances, the clipping should be be tolerated – consider it to be a normal artifact of the encoding process. Be that as it may, in the few tests performed with these recorders, clipping could be entirely avoided in the WMA or MP3 by simply lowering the recording volume using an in-line Level Attenuator.

Frequency Response 

Let’s examine the frequency response of recordings in detail now. Particular detail will be paid to how analogue portable recorders perform as well, which will serve as a benchmark.

The encoder on the Zen will also discard frequencies above the sharp 15.5 kHz cut off so is most suited for FM radio recording. FM broadcasts exhibit approximately the same cut off. Frequencies also sharply rolled off after 16 kHz on the YEPP recordings.

Note that for digitally recording local FM broadcasts, the ADS Tech RDX-155 ($20, new) is the better route, due to the provision of lossless 192 kHz sample rate PCM recording. This Silicon Labs’ SI4701 tuner (marketed as ‘Instant Radio’, above) is a USB computer tuner which requires antenna modifications (including soldering) for connection to a rooftop antenna.

Two test signals were recorded in the Zen. On the left is the original, on the right is the copy. This spectral analysis illustrates the ability of the recording to capture the original.

sweep-zen

test-signaltest-signal-zen

In addition, an eighties rock song was recorded in the Zen.

metropolismetropolis-zen

These measurements are not considered to be problematic; many quality cassette recorders gently roll off content after 18 kHz. It is often suggested that unless one makes recordings with considerable of gong & cymbal percussive content, such high frequency roll off may not even be noticeable.

Vintage JVC one-piece boom box © 2011 Neil.

Vintage JVC one-piece boom box © 2011 Neil.

One low-end boom box tested (manufactured in the late nineties) exhibited little high frequency response after 14 kHz, whilst one high-end boom box tested (manufactured in the mid-eighties) lasted beyond 17 kHz. These had been professionally serviced with new belts fitted as necessary, the digital recorders do not require ongoing servicing.

Below is an example of a high-end boom box recording using Dolby B noise reduction & a medium grade TDK AD tape. Again, on the left is the original, on the right is the copy. Strikingly, the cassette recording significantly outperforms the Zen recording, shown above. But remember this machine has been well maintained; vintage analogue equipment requires ongoing attention if it is to continue performing close to the original manufacturer specifications.

jvc-cd-source-same-old-scenejvc-same-old-scene

Modern boom boxes offer considerably worse compact cassette recording performance than these (above) examples. For instance, observe (below) the performance of a regularly serviced, low-end boom box compared to the Zen digital recording. Whilst there is slightly higher frequency response on the cassette recording, this analogue quality improvement is offset by more hiss (evident in blue, above 12 kHz) than the Zen digital recording, as the low-end boom box recorder provides no noise reduction. In fairness, compression artifacts affect the digital recording (due to low 160 kHz encoding bitrate). Depending on the genre of music being recorded, these digital noises may be as irritating to listen to as audible hiss. It is a matter of personal preference as to which of these two low quality recordings is more natural sounding to listen to.

panasonic-selling-the-dramazen-selling-the-drama

Modern boom boxes (marketing pictures appear below) include the Panasonic RX-D55 (from $182, new) & Sony CFD-S50 (from $117, new).

panasonic-rx-d55

Panasonic RX-D55 boombox.

sony-cfd-s50

Sony CFD-S50 boombox.

Extremely poor recording performance with modern boom boxes is probably because the demand for quality is not strong, like it was in the eighties & nineties. Although currently fashionable amongst indie recording artists, these plastic boom boxes cannot be even recommended for the simple task of playback of pre-recorded cassettes! Today, manufacturers’ research & development priorities are likely to be focused on digital recording.

Final comments

It is hard to dispute that these portable hand held recorders can offer immense convenience & are likely produce higher fidelity recordings than modern low-end boom boxes. Firstly, a laptop or boom box recorder is much larger in size. Secondly, laptops must be regularly maintained with software & perhaps to a lesser extent, hardware upgrades. Boom boxes also require maintenance such as regular head cleaning & very rarely, belt replacement. Ongoing maintenance for these hand held recorders is negligible. Those commitments might include regularly charging the battery & very rarely, updating firmware!

However, the testing of Zen & YEPP indicated evidence of noisy or poor quality A-D conversion in these recorders, compared to even the most basic on board sound cards found in computers. Audio clipping is also a significant potential problem, especially for careless users. The Automatic Level Control cannot be blindly relied upon during recording. These factors potentially contribute to noisy, harsh-sounding or distorted recordings.

Accordingly, the next topic for discussion is the use of simple software for portable recording on superseded or surplus laptops. It is suggested that recording with a computer may allow better quality recordings than hand held recorders because of the less restrictive encoding options, full adjustment of recording levels & options to plug in high-end external sound cards into the computer. But it can be tricky to find free software that simplifies, rather than unnecessarily complicates the process!

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Salvage for salvation: budget FM radios in a post apocalyptic world

Historical records suggest that this electronics shoot out was conducted during a chilly, overcast winter morning. It was as bleak and lifeless as a post nuclear apocalyptic scene akin to the Terminator. It was speculated that a small gang of elitists running the incumbent government had somehow vaporized the masses of decent folk with their relentless, soul-destroying dogma and double talk.

Apocalypse  © 2008 Michael Lehenbauer

Apocalypse © 2008 Michael Lehenbauer

All was not lost. The ‘suits’ had left some populist toys to play with. The few broken souls that remained in the city post apocalypse grabbed their toy radios. These were amongst their only remaining electronic devices. Could these rescue them from sheer desperation?

Graffiti: Greed is deadly © 2007 Bart Everson

Graffiti: Greed is deadly © 2007 Bart Everson

It was rumoured that the internet – the old world hub of information transfer had been sold by the self-interested elite to the highest bidder. Restricted to the highest echelons, few mortals possessed the social connections to enable access to the electronic network that once had the capacity to empower the disenfranchised and wealthy alike. Now, social mobility was virtually impossible.

No weather indicators to were available. Accordingly, tropospheric enhancement to FM signals could be tracked on-line. Synoptic charts were not available. The FM band that did exist was as boring as hell, filled only with those routine permanent FM signals. DX enthusiasts (those that monitored distant radio signals) were a forgotten breed. In this new world order, survival was the only concern. Hobbies became solely the domain of the wealthy.

Wise words, In Greed We Trust © 2014 Ed Suominen

Wise words, In Greed We Trust © 2014 Ed Suominen

But the nightmare was only beginning. It is clear that the poor mortals (those determined few that were left) struggled on with their souls intact. As pointless as it seemed to be in that environment, their capacity to test and experiment would endure.

It is now known that amongst the ruins of their old municipalities they conducted many seemingly fruitless tests. What follows is one such test; a shoot-out. Where possible, the original source material is quoted from…

Populist’s dream radio shoot out

The simpletons focused on two cheap ‘bastards’ with a ‘fearsome’ reputation to uphold. When the economy still functioned, these radios were purchased at retailers like Junk World. It was said that the two machines the simpletons had chosen empowered them, coupled with their tenacity to ‘fight it out until the death’!

Junkworld © 2010 Danny Choo

Junkworld © 2010 Danny Choo

A populist’s dream, the contenders consisted of the ADS Tech RDX-155 Instant Radio USB device versus discounter Aldi’s entry level Bauhn ADS-215 dual band portable radio…

Bauhn Digital Receiver Geeks.com ADS Tech RDX-155 Instant Radio marketing photographs

Testers’ performance data

Table 1: Sensitivity equivalence illustrating selected moderate-weak stations

FREQUENCY  DISTANCE  POWER INSTANT RADIO BAUHN
88.5 53mi 26 kW YES YES
89.3 48mi 25 kW YES YES
90.5 43mi 200 watts YES YES
91.1 35mi 10 kW YES, RDS YES,  RDS
91.7 53mi 26 kW YES YES
92.1 43mi 5 kW YES YES
92.5 48mi 25 kW YES YES
94.1 48mi 25 kW YES YES
94.5 88mi 100 kW YES YES
94.9 26mi 50 kW YES YES
95.3 88mi 100 kW YES YES
95.7 53mi 26 kW YES YES
96.9 88mi 100 kW YES YES
97.7 53mi 26 kW YES YES
98.5 88mi 100 kW YES YES
102.9 25mi 48 kW YES YES
104.1 65mi 1 kW YES YES
105.7 48mi 10 kW YES YES
107.3 48mi 10 kW YES YES

 

Table 2: Marginal signals illustrating reception differences between the two budget receivers

FREQUENCY DISTANCE POWER INSTANT RADIO BAUHN
90.9 25 mi 48 kW 2 / 2 0 / 2 – ACI
95.9 40 mi 1.6 kW 0 / 2 – RFI 2 / 2
96.1 88 mi 100 kW 0 / 2 – RFI 1 / 2
99.4 48 mi 2 kW 2 / 2 1 / 2
100.6 48 mi 2 kW 2 / 2 1 / 2

Salvaging suitable antenna connections

The Bauhn ADS-215 radio was also connected to the rooftop antenna via a 1 m / 3.28 ft high grade RG59 cable. To connect the antenna internally would void the warranty. Moreover, it is difficult to achieve this as the plastic case must be plied open, since there are no screws!

External antenna connection on Bauhn ADS-215 © 2014 FM DXing

External antenna connection on Bauhn ADS-215 © 2014 FM DXing

On the unit, cable was connected to the DC adapter ground [not pictured] and the collapsed telescopic antenna. The radio was powered using the supplied 5 volt DC adapter.

Optionally, if cutting coaxial cables is unpleasant, connection can be easily made via a 30 cm / 1 ft twin-lead wire then a 4:1 matching transformer. To be perfectly honest, transformers do pose some insertion loss as part of any antenna system. Surprisingly, no difference in signal strength of weak stations was detected between connection methods.

RDX-155 Instant Radio was connected to the rooftop antenna via a 1 m / 3.28 ft high grade RG59 cable. This cable also may cause some loss of signal and be susceptible to interference from the USB device. Sure, RG6 quad shield cable is better, but in practice the centre conductor is too thick to reliably connect to a pint- sized USB PCB. The laptop was powered using a battery.

It is speculated that access to laptop computers was not a trivial matter. Computers were  rare and prized possessions in post apocalyptic life. Because access to the internet was predominantly impossible, these computers were useful for processing needs only and recording data.

Fortunately, Instant Radio posed few Central Processing Unit (CPU) demands and looks to have functioned remarkably well on these old machines. How the simpletons ever charged that battery without a reliable mains power grid (they could not afford the onerous electricity bills) remains a mystery…

Post apocalyptic broadcasting

Records show that only an FM test was possible. But it was noted (amongst the word processing files found) that with the Bauhn dual band radio, full strength DAB+ reception (174 – 240 MHz) was available with the rooftop antenna. Photos were found of the graphical bars of the signal meter. Its Gyro Signal 1128 chip permitted satisfactory dual band reception at this time. (We don’t know the manufacturer’s objective sensitivity measurements for this module, but an Adobe Reader document with the FM performance of their 2005 module can be found via the end links). Retailing at $30, the Bauhn ADS-215 radio was likely to be an affordable choice for those with limited fiscal capabilities.

No contemporary music was being released or recorded. The broadcasts on the DAB+ multiplexes in these times included songs performed by old school cover bands such as Il Divo & Celtic Thunder. Music that was deemed to be fodder for the oppressed was reportedly banned for broadcast. For example, ‘aggressive’ releases by Neil Young, Metallica, the Dixie Chicks & John Butler Trio were illegal to broadcast, even if the recordings had been retained by some members of the elite. It has been suggested that the themes in these artists’ works may have been incompatible with the extremist ideology of the ruling elite…

Bauhn ADS-215 post Apocalypse © 2014 FM DXing

Bauhn ADS-215 post Apocalypse © 2014 FM DXing

Luxurious RDS performance suggested

Seven signals in the [above] table are known to provide digital Radio Data System (RDS) data. Six of these signals were too weak to decode. Only one quieting-level signal was included in the test, a broadcast on 91.1 MHz. On this channel, RDS data decoded easily on both units. RDX-155 Instant Radio offers faster decoding than the Bauhn ADS-215 radio. The Programme Type data (alone) decoded reasonably quickly on the Bauhn radio, but Instant Radio has a clear edge.

PI code mode on Bauhn ADS-215 © 2014 FM DXing

PI code mode on Bauhn ADS-215 © 2014 FM DXing

Close up, PI code mode on Bauhn ADS-215 © 2014 FM DXing

Close up, PI code mode on Bauhn ADS-215 © 2014 FM DXing

The Bauhn ADS-215 radio will display unique station identification codes called PI codes as part of the RDS digital data. This feature may offer potential value for DXing.

Post war, it is known that the elite took control of electronics and computing power. Whilst the elite played real life games on the stock market, the mortals continued their desperate simple tests. Trivial? Indeed. But it is all they had. They continue…

Riding out the Apocalypse © 2011 David Blackwell

Riding out the Apocalypse © 2011 David Blackwell

Differences testers observed

Where differences were noted between receivers on any particular frequency, the test was conducted twice. Between 95.9 – 96.1 MHz, no signal was heard due to heavy interference obstructing potential reception on RDX-155 Instant Radio. The interference was caused by a spurious signal.

This annoying side effect is a widely reported issue with the device that cannot be readily remedied by ferrite suppression chokes. It will be offset by a masthead amplifier, of course. Conversely, no spurious signals were observed on the Bauhn ADS-215.

Bauhn ADS-215 post Apocalypse © 2014 FM DXing

Bauhn ADS-215 post Apocalypse © 2014 FM DXing

On 99.4 MHz & 100.6 MHz, only weak signals were detected. Nonetheless,  RDX-155 Instant Radio appeared to outperform its rival in terms of sensitivity. On 90.9 MHz, no signal was detectable due to adjacent channel interference obstructing potential reception of the broadcast on the Bauhn radio. Again, this suggests selectivity out-performance by the Silicon Laboratories’ (Silabs) integrated circuit inside in the Instant Radio.

It is thought that back in the ‘olden days’, Silabs produced radio electronics that every man, woman or android could afford. Although Silabs mainly produced chips for portable standalone radios at this time, the RDX-155 Instant Radio represented somewhat of an oddity; a discontinued $17 computer-based tuner in a tiny USB enclosure.

Intermodulation dynamic range was tested on empty or very weak channels. Strong signal immunity is extremely important for FM reception applications and arguably a more important characteristic for any FM tuner than any simplistic sensitivity measurement or test. It is pleasing to report that no ‘ghost signals’ were detected on either receiver, despite the congested band. Accordingly, a high quality signal amplifier (ideally a masthead amplifier, positioned at the antenna) may increase sensitivity without compromising performance.

Instant FM Radio post Apocalypse © 2011 Synx 508

Instant FM Radio post Apocalypse © 2011 Synx 508

Simpletons’ summarized observations

The test (as collated in the table) suggests that potential differences in sensitivity, (if any exist) are likely to be negligible between ADS Technologies’ RDX-155 Instant Radio & Aldi’s Bauhn ADS-215. Weaker signals, such as the 90.5 MHz translator are not readily detected in flat winter conditions. The performance of Instant Radio was superior on three stations (probably due to better sensitivity and selectivity) but internally generated interference tended to offset any gains.

These findings suggest that the simpletons were confident both units would provide satisfactory FM reception for the modest outlay they originally paid at retailers like Junk World.

The broken souls understood a masthead amplifier could be used with these inexpensive receivers to improve performance when coupled with an external antenna.

Junk electronics © 2007 Marco Bernardini

Junk electronics © 2007 Marco Bernardini

It was beyond the means of most, but they found some antenna pre-amplifiers on the streets; regrettably their beloved streets had become so littered with redundant electronics their suburbs resembled a rubbish dump. These cheap radios gave the broken souls hope for the future. Finally their story of hope can now be shared for the benefit of future generations.

Society’s future is unwritten. Government policy or individual action that promotes greed, entrenches class divisions & exacerbates poverty is the real ‘junk’ of the world!

Non-fiction reference material!

Extensive test of Instant Radio RDX-155

Boxing kangaroo test of Bauhn ADS-215

Gyrosignal 1122 FM/DAB receiver module specifications

Masthead amplifiers potentially benefit weak FM signals

Role of RDS data in long distance FM reception

FM USB Tuner Shootout: PC Ear vs Instant Radio (ADS Tech RDX-155)

Welcome to another radio shootout, Boxing Kangaroo edition! These shootouts feature ‘dirt cheap’ radios and are intended to appeal to a variety of different potential audiences, including terrestrial FM radio listeners and hobbyists interested in elementary electronics or FM reception capabilities.

Boxing Kangaroos in the zoo © 2011 Scott Calleja

Digital Signal Processing on the cheap?

At the time of writing, the cheapest Chinese portable FM radio currently available incorporating Silicon Labs’ (Silabs) Digital Signal Processing (DSP) costs about $49 including delivery. This model is the Tecsun PL-606. For those with a laptop and access to a directional antenna, USB computer devices with the SI4700/01 integrated circuit (IC) are considerably more inexpensive, representing a cheap entry to Silabs DSP.

 Tecsun CR-1100 © 2013 James Case

 Tecsun PR-380 © 2013 James Case

The contenders: Two popular Silabs USB FM tuner

Instant FM Radio (Instant Radio) costs about $17 including delivery.

USB FM Radio Player © 2005 Silicon Laboratories

MP3car.com ADS Tech RDX-155 Instant Radio under Windows 7, Canberra Australia

Geeks.com ADS Tech RDX-155 Instant Radio marketing photographs

PC Ear FM Radio Player © 2014 FM DXing

PC Ear costs about $17 wholesale but is no longer readily available new.

PC Ear unboxed © 2014 FM DXing

Gunning for the best: PC Ear versus Instant Radio

A rudimentary inspection of the datasheets suggest the FM sensitivity measurements are equivalent for the Silabs ICs inside PC Ear and Instant Radio. To test this, a modest directional antenna was connected to the devices. Both devices were housed in a metal enclosure with two suppression chokes and operated with a Radio Frequency (RF) quiet laptop running from battery power.

Reception conditions were well below average with heavy, unrelenting rain. 15 stations were chosen for the test. Of these, 13 stations were detected with the minimum signal strength of 0, where signals are just audible above the noise floor. Because of the heavy rain, two of the usual weak signals were not audible during the test and accordingly, do not appear in the performance table.

Software

PC Ear does NOT support firmware upgrades using the Windows-based Silabs configuration software utility. Firmware updates to PC Ear can be done under Ubuntu/Linux, but the process may be complicated. The Silabs Radio DLL software appears to function, but audio issues were evident when tested briefly with PC Ear. According to the developers, it is supported.

The upgraded firmware was used with Instant Radio. The upgrade was performed per the ADS Configuration user guide instructions for Silabs Radio DLL, developed by Beezer, Guino and Pete.

Characteristic PC EAR  INSTANT RADIO
Tunable frequency range 76 – 90 MHz, 87.5 – 108 MHz 76 – 90 MHz, 87.5 – 108 MHz
Circuit board approximate size 1.3 x 0.6 inches 2.4 x 1.1 inches
Tuning steps 50 kHz 50 kHz
Radio Data System support No Yes
Software support USB Radio 2.0-3.0 (supplied), FM Signal Strength Analyzer 1.0.0.19, Silabs Radio DLL, Silabs configuration software utility. Instant Radio 1.0.0.11 (supplied), Silabs Radio DLL, FM Signal Strength Analyzer 1.0.0.19, Silabs configuration software utility.
Hardware version PC Ear 1.77 Silabs 1.7.15
Firmware upgradable No, Please refer to body of article Yes, ADS NoiseMod Primary.dec

The software support listed in the characteristics table (above) is NOT exhaustive. Please understand that the priority was to test reception performance.

Any frequency (or broadcast) can be easily recorded for hours ‘on schedule’ using third party Windows audio recording schedule software such as Fox Magic Audio Recorder (free) and High Criteria Total Recorder Professional ($36). The software supplied with the devices also offers recording ‘on demand’. ADS Tech Instant Radio software is especially recommended for this purpose, since it offers high resolution 96 kHz uncompressed recording capabilities.

Closeup of ADS Tech Instant FM Music PCB © 2014 FM DXing

Comparative performance

PC Ear is constructed on a double sided printed circuit board, whilst the Instant Radio device uses a much larger single sided board (above). Unsurprisingly, both designs feature surface mount components.

RADIO STATION FREQUENCY (MHz) PC EAR MAXIMUM SIGNAL STRENGTH (BARS) INSTANT RADIO MAXIMUM SIGNAL STRENGTH (NUMBER) INSTANT RADIO RDS DECODING DISTANCE (MILES)
90.5 0 3 No 43mi (200 W)
91.1 2 – Quieting Mono 19 – Quieting Mono Instant 35mi
92.1 0 6 N/A 43mi
93.7 0 0 N/A 62mi
94.9 0 6 No 27mi
95.3 1 6 N/A 88mi
98.5 1 – Quieting Mono 9 – Quieting Mono N/A 88mi
99.4 0 0 No 48mi (2 kW)
99.5 No signal, Slight high adjacent channel interference (99.7) 0 N/A 208mi
102.9 0 6 N/A 48mi
104.5 4 – Quieting Stereo 50 – Quieting Stereo Instant 11mi
105.7 0 5 No 48mi
107.7 5 – Quieting Stereo 57 – Quieting Stereo N/A 11mi

Instant Radio consistently offered a slight edge with superior adjacent channel suppression on one station and the advantage of RDS. PC Ear did ‘stutter’ occasionally on one RDS-enabled station. A change to the device settings (below) and immediately unplugging the device solved the problem. This trivial audio issue could not be replicated again after 15 minutes of listening to the station, nor the next day.

PC Ear FM Radio Player custom settings © 2014 FM DXing

There were no consistently observable differences in sensitivity, audio quality or immunity to internally-generated spurious noise (interference) between the devices. This result was somewhat unexpected because PC Ear is rumoured to be an earlier Silabs USB tuner prototype with its share of critics on the world wide web. Perhaps the critics use the supplied wire antenna (in both devices, 29 inches long) and therein lies the problem? But the test suggests PC Ear performs just as well as Instant Radio with a directional antenna. If anything, the test was biased against PC Ear because of expectations the device was of poor design quality relative to its sister models.

Performance improvements

It should be stressed that Instant Radio and other Silabs devices require antenna modifications (below) for connection to a directional antenna such as a rooftop television antenna. Soldering skills are recommended for permanence. The use of other alternatives to ‘mate’ the device with an external antenna, such as passive induction as used in some mobile broadband device antennas might also be feasible, but discussion is beyond the scope of this shootout.

With the additional expense of a metal enclosure, shielded five metre USB cable, pre amplifier and several ferrite suppressors, the total cost equates to approximately $135. Many readers may already own much of this equipment, but it does represent a potential outlay. In this blogger’s opinion it is only worth pursuing such a project for the sheer fun of experimentation!

Instant Radio customization © 2014 FM DXing

Notwithstanding the extra Do It Yourself (DIY) effort and cost required to extract the device’s DX potential, Silabs tuners feature satisfactory signal separation and strong signal handling. With the above modifications, Instant Radio is sensitive enough for daily signals from in excess of 265 miles. Momentary meteor pings from distant FM stations are possible to receive. Although untested at the time of writing, it is anticipated that modifications to PC Ear would accomplish the same. The bottom line is that these Silabs devices were designed for learning projects. It is NOT suggested to ‘throw good money after bad’.

Comparative performance with expensive stand alone tuners

As one should realistically expect because of the tiny footprint and price, the devices are outclassed by stand alone tuners with a proper shielded tuner module. Even with a preamplifier used in-line to desperately boost sensitivity, this is apparent. Head-to-head, the following tuners or SDRs (tested without preamplifiers, using the same antenna) all noticeably outperform Instant Radio (FM usable sensitivity* is listed in brackets):

  • Blaupunkt Casablanca CD51 (1.68 microvolts),
  • Elad FDM-S2,
  • Sherwood TX-5090 RDS (1.58 microvolts),
  • Yamaha TX-950 (0.8 microvolts).

For example, in a ‘dead-of-winter’ test, the Blaupunkt automotive receiver consistently achieved better performance than Instant Radio. Improved RDS sensitivity meant that the car radio decoded digital RDS data from two extra stations. Like all models in the Sharx range, the car radio more readily discriminated stations spaced 100 kHz apart.

Instant Radio was capable of receiving 2/3 of the 15 weak signals chosen for the test, whilst the car radio nabbed 93% of weak signals! The Silabs devices enable reception of the same stations from in excess of 265 miles as standalone tuners. However, this reception will obviously be more transient and weaker signals are unlikely to be audible. From a DX enthusiast’s perspective, that may be a frustrating prospect.

The number of RDS decodes achieved with Instant Radio was equivalent to the Bauhn ADS-215 dual band portable radio connected to a carefully aligned rabbit ears antenna mounted near a window. Invariably, Instant Radio outperformed the Bauhn portable radio using its inbuilt telescopic antenna.

DealeXtreme.com PC Ear marketing photographs

Summary

The device incorporating the Silicon Labs’ SI4701 IC (marketed as ‘Instant Radio’, above) is one breed of flash-drive sized computer tuner that offers modest potential for weak FM signals. It suits receiving locations with a congested FM band. Its full RDS capabilities can be exploited in locations where broadcasters support the system. PC Ear also offers similar performance, without RDS decoding.

All software tested works successfully on both receivers without noticeable bugs. There is a range of tuning software to choose from. Both Silabs devices are suited to DIY modifications.  Users of Instant Radio benefit from access to the latest firmware.

Further reading

Gadget tunes in to FM via USB

Instant Radio for distant FM reception

Instant Radio satirical shootout

Instant Radio slideshow

Radio recording saved the radio star

Silabs Radio DLL

* Standard DIN sensitivity specifications, tested with THD 3% & S/N of 26 dB. Official data, sourced from manufacturers. Lower numbers (approaching zero) indicate the best FM sensitivity. The Elad FDM-S2 sensitivity is measured differently from conventional tuners. This SDR offers better than 2 microvolts using the 12dB SINAD measurement on the extended FM band.

As always, the writer has no affiliation with any retail merchant or product manufacturer. This entry is NOT intended to be construed as an endorsement of any particular model. Prospective buyers should carefully make their own enquiries according to their particular needs and circumstances.