Grabando grabaciones a 78rpm

Este tutorial detalla los pasos necesarios para procesar grabaciones a 78rpm con Audacity:

• Idealmente use una tornamesa con velocidad ajustable y de 78rpm - a pesar de que usted puede realizarlo a menor velocidad.
• Use una aguja para 78rpm - usted puede querer usar un cartucho separado.
• Limpie sus grabaciones a fondo.
• Use los ajustes predeterminados de Audacity: un formato de muestreo de 32-bit flotante y una frecuencia de muestreo de 44100 Hz
• Procesando para ajustar la ecualización y remover el ruido - y revisar los resultados.
• Exportar a WAV/MP3 de la forma normal.

Resumen del procedimiento

1. Limpiar las grabaciones
2. Grabando una captura con Audacity
3. Exportar a WAV como respaldo maestro
4. Remover cualquier desalineación DC que pueda estar presente
5. Invertir la ecualización RIAA
6. Corregir la velocidad con el efecto de Cambio de velocidad
7. Aplique la ecualización correcta (la que sea necesaria)
8. Filtrar para remover los ruidos de alta y baja frecuencia
9. Limpiar clics y otros ruidos aleatorios
10. Ajustes de volumen - normalizad y compresión
11. Revisar
12. Exportar como WAV, MP3 u otro
13. Respaldar (usted no querrá perder todo este trabajo invaluable)

Use una aguja o cartucho especial

Usted no debiera usar una aguja normal para reproducir a 78rpm. Los graves a 78rpm son mucho más anchos y profundos que en un LP, por lo que una aguja normal tocará el fondo de las ranuras en los bajos y también rebotará de lado a lado en los pasajes más fuertes. Esto resultará en:

• ruido, transferencias con mayor silbido
• una reproducción mucho menos exacta de la música
• daños a la aguja que después funcionará incorrectamente en LPs

Revise el sitio web o manual de su tornamesa para ver si el fabricante suministra una aguja o cartucho especial para 78 rpm. Si no, busque en la web por "aguja 78 rpm". Un típico inicio correcto es una aguja de zafiro de tamaño de 3mm, pero revise cuantos lados reproducirá ya que la aguja no dura tanto como una de diamante.Los graves típicos en grabaciones de 78rpm anteriores a 1940 van desde los 2.5 a los 4mm, y grabaciones de 1920 y anteriores varían aún más.

Use un cartucho diferente
Si usted puede pagarlo, use un cartucho separado del que usa para sus LPs. Usted necesita uno que pueda soportar ir a los 4 o 5 gramos de peso que la mayoría de las grabaciones de 78 rpm necesitan. Idealmente usted debiera considerar más de un ancho de aguja si usted está reproduciendo grabaciones en laca realmente antiguas, porque en no hubo un estándar de dimensión de graves hasta finales de la era de los 78 rpm. Nuevamente, busque en Internet por consejos.

Use un portacápsulas de recambio
La forma más segura de cambiar entre tipos de agujas (si usted lo hace a menudo) es usar un portacápsulas separado y un cartucho. De esta forma usted no estará cambiando continuamente la aguja en su cartucho - un procedimiento riesgoso.

Limpiando las grabaciones

Intente limpiar las grabaciones lo más exhaustivo que pueda antes de grabar. Esto le salvará tiempo cuando tenga que limpiar los chasquidos y clics que son un trabajo difícil si lo realiza manualmente.

No use solventes basados en alcohol en la laca, use solo limpiadores basados en agua o agua. Usted puede usar un poco de líquido de limpieza en una pieza de tela y agua tibia. Dele un lavado completo en agua fría, no caliente, y colóquelo en un escurridor para platos - luego cambie el agua y enjuague profundamente - finalmente enjuague con agua destilada (des-ionizada), luego escurra y seque con un pedazo de trapo seco.

Evite limpiar con papel de cocina o similar, ya que es abrasivo y puede dejar fibras atrapadas en los graves. Si usted está en apuros, colocar la grabación en una pieza de papel de cocina puede absorber la mayoría del agua destilada, pero evite limpiar la grabación.

Usted nunca debe intentar reproducir un disco de laca cuando está mojado.

Reparar

Fairly obviously, do not record warped, cracked or badly chipped records. With a certain amount of patience, problems such as this can be repaired.

Equalization

When recording 78 rpm's, there is a problem that the pre-amplification built into any consumer-level pre-amplifier or USB turntable will be designed for vinyl records made from the 1950s onwards. This is because the pre-amplification not only provides the necessary amplification for the cartridge signal that is sent to Audacity, but applies what is known as "RIAA playback equalization" to it. This equalization is essential when playing records made from the 1950s or later, as it cancels out the high frequency biased "RIAA recording equalization" that such records are cut with, making them sound normal again. The problem is that most 78 rpm records were not cut with such a strong high frequency bias. They therefore sound dull if played through modern equipment that applies RIAA playback equalization.

So, to make a fully professional job of transferring your 78 rpm records, you should open Effect > Equalization in Audacity immediately after recording, and apply the inverse of the RIAA playback curve (see the next section). This will cancel out the unwanted RIAA equalization, after which you can apply one of the 78 rpm playback curve presets supplied with the effect. Note that the 78 rpm curves are generic. In practice, many different equalizations were used according to the record label or even the recording engineer. See 78rpm playback curves in the Audacity Wiki for a list of known equalizations used by different manufacturers of 78rpm records.

Inverting the RIAA curve

You can select the "RIAA" curve, then use the "Invert" button to invert it. Then apply that equalization to the recording

The Invert button provides other opportunities for correcting inappropriate equalization. For example, if you were recording an acoustic record on equipment that could only reproduce one of the listed "78" or "RCA" curves meant for electrical 78's, you could invert that curve, then apply the very different "acoustic" curve. The result would not be ideally accurate, but far better than not changing the equalization at all.

Lower speed dubbing - 33 1/3 or 45rpm

If your turntable does not have the facility to play records at 78rpm, you can use Audacity's ability to change the speed of recordings to record your 78 rpm records at either 33 1/3 rpm or 45 rpm. Since you are playing the disk slower than normal, tracking should not be an issue. The top frequency on a 78 will be around 8 kHz, and playing it slower will lower that to about 4.6 kHz.

Gale: On reflection, is the below div in the best place? Perhaps it should be in "Note on actual speeds"? There are several cases a) record really is a later electrical disk meant for 78 rpm but the fixed speed t/t is actually going at 75 rpm. b) Fixed speed t/t correctly goes at 78 rpm, 33 1/3 or 45 rpm but we have an 85 rpm record. In all these cases don't we need the formula to decide the change speed percentage to apply?

If your turntable doesn't have a strobe or speed adjustment, you can measure the playback speed in revolutions per minute (RPM) very accurately thus:

1. Record the leadout of the final groove and select the distance between the recorded clicks in the Audacity waveform
2. Measure the time taken for 10 consecutive revolutions (you can measure to 1/1000 of a second by zooming in on the waveform)
3. Divide that time by 10 (for example, if you measured 8 seconds, dividing that by 10 gives you a resultant value of 0.8)
4. Divide the resultant value into 60 (in our example, 60/0.8 gives us the answer that the record was playing at 75 RPM)

Record the track into Audacity at your chosen speed and then simply select all the track by clicking in the Track Control Panel (where the mute/solo buttons are) and click Effect > Change Speed. In the "From" box choose the speed you played the record at (for example, "33 1/3" or "45") and in the "To" box choose the speed you want to convert the recording to (i.e. the speed it should be played at according to the label).

Note that you should reverse the RIAA equalization before changing speed - now the transfer is "flat". Then change the speed. Then apply the "proper" 78 rpm equalization (whatever that may be). So the workflow steps for this part of the process are:

1. Record the 78 at 45 or 33 1/3
2. Apply the Inverse RIAA EQ (to make it like a "flat" recording)
3. Change the speed to 78rpm
4. Apply appropriate EQ for what the 78 was recorded with

Note on actual speeds: With the early clockwork turntable mechanisms the rotational speed was rather approximate and manufacturers produced records in the 70 to 90rpm range with 78 being the most commonly accepted “standard”. Many disks had the speed stamped on the label and they depended on the early players which had a speed control. With the introduction of the synchronous AC motor, for detailed technical reasons, the standard was changed to 78.26 rpm. See this website for details: http://www.videointerchange.com/vintage_78s.htm

Stanton T-series USB turntables still offer 78rpm working, and helpfully they have a wide speed adjustment range. If you know exactly what speed your records should spin at you can find a strobe disk on the Internet and print one out with exactly the right spacing of bars. One example site is: http://www.78rpm.com/rescat/strobe_info.htm.

Filtering & noise removal

Noise on 78's is complex, and relatively high in level. You will need to try to reduce some of the different types of noise in separate passes.

Noise removal

Gale 02 Apr 11: Should we completely bypass Audacity Noise Removal here? Are we saying that noise removal is a marginal activity after filtering, which I seem to sense reading between the lines?

• Peter 9Oct11: No I don't think we are saying or even hinting that. What we are saying is that currently there are better tools than Audacity for performing this particular, focussed, section of the overall task. It is ceratinly not a "marginal" part of the task, particularly with old 78s

Over the years your 78s will undoubtedly have received scratches and wear, which will result in clicks, pops and crackle. Audacity does have tools for click removal and noise removal - but there are better tools than Audacity for removing these, although "Effect > Repair" works extremely well for removing single clicks.

Some of these tools do cost some money but most have free-trial periods. Goldwave is often recommended by Audacity users, as are Brian Davies' ClickRepair and DeNoise packages.

Filtering

1. Make sure you have set the Audacity Default Sample Format in the Quality Preferences to 32-bit float (the default) because you are probably going to do a fair bit of processing, and some of the filters appear to work better with 32-bit input.
2. Perform DC offset correction by using Effect > Normalize, checking the "Remove any DC offset" box but (for now) unchecking the "Normalize" box.
3. Then run Effect > Low Pass Filter to remove high frequency noise - set the cutoff frequency to suit the vintage of the record. For recordings from the 1940s or later set the cutoff frequency at 9 kHz or 10 kHz; for electrical recordings (1926 to 1939) about 8 kHz, and acoustic recordings (before 1926) about 7 kHz. Use a rolloff of at least 12 dB per octave; 24 dB per octave could probably be better. Listen to the result to make sure the sudden cut-off of high-frequency noise does not sound too artificial.
4. Then deal with the low frequency noise - select a "noise sample" from the current audio track (that is, a section of the recording that is surface noise only) and copy it to a new track. Use Analyze > Plot Spectrum to see the frequency content of the noise. Use the low pass effect on this noise sample to isolate the lower frequency noise, (for a very rough and ready setting, try a rolloff of 12 dB per octave at a cutoff frequency of 1000 Hz). Then open Effect > Noise Removal, select the low-passed noise sample and choose "Get Noise Profile". Finally, select the original track, open Noise Removal again, choose the slider settings and run the effect.

An alternative, simpler, method for dealing with low frequency noise is to use Effect > High Pass Filter to filter out frequencies below 20 Hz. It's amazing that the waveform can display these sub-sonic frequencies, usually deficiencies in the cutting lathe during the original recording session.

Click Removal

Remove any clicks and pops from the recording using Effect > Click Removal - or using alternative third party software as discussed above.

Normalization & Compression

As a final step you may wish to adjust the loudness of you recording.

Normalize

You can use Effect > Normalize to bring the maximum volume of your recording to a specified level - we would suggest to around -3.0 dB. Audacity's Effect > Amplify can also be used for the same function. Normalize has the advantage that it can be optionally set to adjust for channel imbalance.

Compression

As a final step, to increase the perceived loudness and density of the recording, more advanced users can perform compression on the recording. You can use Audacity's Effect > Compressor to do this.

There are also some alternative free compressors available as separate downloads which work well with Audacity.

Review & Export

Then review the track to decide if any further treatment is required, or if you need to restart from scratch. If you are happy with your work than your project is ready for Export to WAV and/or MP3 etc.

Backup

Don't forget to backup your finished audio files as you will not want to lose all that hard work; ideally at least two separate copies on separate media. You may wish to consider also backing up your original capture masters as WAV files, then you can always come back to the raw recording later and re-process it if you need or want to.

Don't expect miracles with badly worn records. The process can be very frustrating and the results can be disappointing. Avoid aggressive denoise. The artifacts are usually worse than the noise. Some users like to leave a little surface noise in their transfers (they are 78s after all!). Declick and equalization are the most important steps in the process. Learn to read the waveform. Sometimes an equalization can increase the amplitude of some frequencies to a clipping level, so consider reducing the amplitude slightly before equalization.

Enlaces

|< Tutorial - Copiando casetes, LPs o minidiscs a CD

>  Vea también el tutorial en: Procedimiento de ejemplo para digitalización de LP

El siguiente sitio: http://www.videointerchange.com/vintage_78s.htm entrega un enfoque purista detallado sobre capturar en alta calidad transferencias desde 78rpm - se merece su lectura si usted es serio sobre este tema.

Brian Davies ofrece un programa gratuito de "Ecualización" que aplica de forma simultanea la curva RIAA inversa, corrige diferentes velocidades de reproducción, y tiene una opción de una curva de ecualización de 78rpm. Vea: http://www.clickrepair.net/